do sailboat masts attract lightning

Yachting Monthly

• Digital edition

Sailing in lightning: how to keep your yacht safe

• In partnership with Katy Stickland
• July 22, 2022

How much of a concern is a lightning strike to a yacht and what can we do about it? Nigel Calder looks at what makes a full ‘belt and braces’ lightning protection system

Storm clouds gather at Cowes, but what lightning protection system, if any, does your boat have for anchoring or sailing in lightning? Credit: Patrick Eden/Alamy Stock Photo

Most sailors worry about sailing in lightning to some extent, writes Nigel Calder .

After all, going around with a tall metal pole on a flat sea when storm clouds threaten doesn’t seem like the best idea to most of us.

In reality, thunder storms need plenty of energy, driven by the sun, and are much less frequent in northern Europe than in the tropics.

However, high currents passing through resistive conductors generate heat.

Small diameter conductors melt; wooden masts explode; and air gaps that are bridged by an arc start fires.

Sailing in lightning: Lightning is 10 times more likely over land than sea, as the land heats up more than water, providing the stronger convection currents needed to create a charge. Credit: BAE Inc/Alamy Stock Photo

On boats, radio antennas may be vaporised, and metal thru-hulls blown out of the hull, or the surrounding fiberglass melted, with areas of gelcoat blown off.

Wherever you sail, lightning needs to be taken seriously.

Understanding how lightning works, will help you evaluate the risks and make an informed decision about the level of protection you want on your boat and what precautions to take.

Most lightning is what’s called negative lightning, between the lower levels of clouds and the earth. Intermittent pre-discharges occur, ionising the air.

Whereas air is normally a poor electrical conductor, ionised air is an excellent conductor.

These pre-discharges (stepped leaders) are countered by a so-called attachment spark (streamer), which emanates from pointed objects (towers, masts, or lightning rods) that stand out from their surroundings due to their height.

Summer is the season for lightning storms in the UK. Here, one finds early at Instow, Devon. Credit: Terry Matthews/Alamy Stock Photo

This process continues until an attachment spark connects with a stepped leader, creating a lightning channel of ionised air molecules from the cloud to ground.

The main discharge, typically a series of discharges, now takes place through the lightning channel.

Negative lightning bolts are 1 to 2km (0.6 to 1.2 miles) long and have an average current of 20,000A.

Positive lightning bolts are much rarer and they can have currents of up to 300,000A.

Preventing damage when sailing in lightning

A lightning protection system (LPS) is designed to divert lightning energy to ground (in this case the sea), in such a way that no damage occurs to the boat or to people.

Ideally, this also includes protecting a boat’s electrical and electronic systems, but marine electronics are sensitive and this level of protection is hard to achieve.

Lightning protection systems have two key components: First, a mechanism to provide a path with as little resistance as possible that conducts a lightning strike to the water.

This is established with a substantial conductor from an air-terminal to the water.

Components of an external and internal lightning protection system. Credit: Maxine Heath

This part of the LPS is sometimes called external lightning protection.

Second, a mechanism to prevent the development of high voltages on, and voltage differences between, conductive objects on the boat.

This is achieved by connecting all major metal objects on and below deck to the water by an equipotential bonding system.

Without this bonding system high enough voltage differences can arise on a boat to develop dangerous side flashes.

The bonding system can be thought of as internal lightning protection.

Rolling ball concept

Lightning standards, which apply ashore and afloat, define five lightning protection ‘classes’, ranging from Class V (no protection) to Class I.

There are two core parameters: the maximum current the system must be able to withstand, which determines the sizing of various components in the system, and the arrangement and number of the air terminals, aka lightning rods.

Let’s look at the arrangement of the air terminals first. It is best explained by the rolling ball concept.

A lightning strike is initiated by the stepped leaders and attachment sparks connecting to form the lightning channel.

The distance between the stepped leader and the attachment sparks is known as the breakdown distance or striking distance.

If we imagine a ball with a radius equal to the striking distance, and we roll this ball around an object to be protected, the upper points of contact define the possible lightning impact points that need to be protected by air terminals.

Lightning protection theories and classifications rely on a ‘rolling ball’ concept to define requirements, areas of risk and protected areas. Credit: Maxine Heath

The air terminal will theoretically provide a zone of protection from the point at which the terminal connects with the circumference of the rolling ball down to the point at which that circumference touches the water.

The shorter the striking distance, the less the radius of the rolling ball and the smaller the area within the protection zone defined by the circumference of the rolling ball.

The smaller the protection zone, the more air terminals we need. So, we use the shortest striking distance to determine the minimum number and location of air terminals.

Class I protection assumes a rolling ball radius of 20m; Class II assumes a rolling ball radius of 30m.

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Boat building standards are based on a striking distance/rolling ball radius of 30m (Class II).

For masts up to 30m above the waterline, the circumference of the ball from the point at which it contacts the top of the mast down to the water will define the zone of protection.

For masts higher than 30m above the waterline, the ball will contact the mast at 30m and this will define the limit of the zone of protection.

If Class I protection is wanted, the radius of the ball is reduced to 20m, which significantly reduces the zone of protection and, on many larger recreational boats, may theoretically necessitate more than one air terminal.

Protection classes

With most single-masted monohull yachts, an air terminal at the top of the mast is sufficient to protect the entire boat to Class I standards.

The circumference of the rolling ball from the tip of the mast down to the surface of the water does not intercept any part of the hull or rig.

However, someone standing on the fore or aft deck might have the upper part of their body contact the rolling ball, which tells us this is no place to be in a lightning storm.

Some boats have relatively high equipment or platforms over and behind the cockpit.

Protection classes to protect your boat while anchored or sailing in lightning

These fittings and structures may or may not be outside the circumference of the rolling ball.

Once again, this tells us to avoid contact with these structures during a lightning storm.

Ketch, yawl, and schooner rigged boats generally require air terminals on all masts, except when the mizzen is significantly shorter than the main mast.

The external LPS

The external LPS consists of the air terminal, a down conductor, and an earthing system – a lightning grounding terminal.

The down conductor is also known as a primary lightning protection conductor.

All components must be sized to carry the highest lightning peak current corresponding to the protection class chosen.

In particular, the material and cross-sectional area of the air terminal and down conductor must be such that the lightning current does not cause excessive heating.

The air terminal needs to extend a minimum of 150mm above the mast to which it is attached.

A graph depicting NASA’s record of yearly global lightning events. The Congo once recorded more than 450 strikes per km2

It can be a minimum 10mm diameter copper rod, or 13mm diameter aluminum solid rod.

It should have a rounded, rather than a pointed, top end.

VHF antennas are commonly destroyed in a lightning strike.

If an antenna is hit and is not protected by a lightning arrestor at its base, the lightning may enter the boat via the antenna’s coax cable.

A lightning arrestor is inserted in the line between the coax cable and the base of the antenna.

It has a substantial connection to the boat’s grounding system, which, on an aluminum mast, is created by its connection to the mast.

In normal circumstances, the lightning arrestor is nonconductive to ground.

When hit by very high voltages it shorts to ground, in theory causing a lightning strike to bypass the coax – although the effectiveness of such devices is a matter of some dispute.

Down conductors

A down conductor is the electrically conductive connection between an air terminal and the grounding terminal.

For many years, this conductor was required to have a resistance no more than that of a 16mm² copper conductor, but following further research, the down conductor is now required to have a resistance not greater than that of a 20mm² copper conductor.

For Class I protection, 25mm² is needed. This is to minimise heating effects.

Let’s say instead we use a copper conductor with a cross-sectional area of 16mm² and it is hit by a lightning strike with a peak current corresponding to Protection Class IV.

Sailing in lightning: This catamaran relies upon cabling to ground from the shrouds but stainless steel wire is not a good enough conductor. Credit: Wietze van der Laan

The conductor will experience a temperature increase of 56°C. A 16mm² conductor made of stainless steel (for example, rigging ) will reach well over 1,000°C and melt or evaporate.

Shrouds and stays on sailboats should be connected into a LPS only to prevent side flashes.

The cross-sectional area of the metal in aluminum masts on even small sailboats is such that it provides a low enough resistance path to be the down conductor.

Whether deck- or keel-mounted, the mast will require a low resistance path, equivalent to a 25mm² copper conductor, from the base of the mast to the grounding terminal.

Grounding terminal

Metal hulled boats can use the hull as the grounding terminal. All other boats need an adequate mass of underwater metal.

In salt water this needs a minimum area of 0.1m². In fresh water, European standards call for the grounding terminal to be up to 0.25m².

A grounding terminal must be submerged under all operating conditions.

An external lead or iron keel on monohull sailing boats can serve as a grounding terminal.

This owner of this Florida-based yacht decided to keep the keel out of the equation when is came to a grounding plate. High electrical currents don’t like sharp corners, so a grounding plate directly beneath the mast makes for an easier route to ground. Credit: Malcolm Morgan

In the absence of a keel , the cumulative surface area of various underwater components – propellers, metal thru-hulls, rudders – is often more than sufficient to meet the area requirements for a grounding terminal.

However, these can only be considered adequate if they are situated below the air terminal and down conductor and individually have the requisite surface area.

Metal through-hulls do not meet this requirement.

If underwater hardware, such as a keel, is adequate to be used as the grounding terminal, the interconnecting conductor is part of the primary down conductor system and needs to be sized accordingly at 25mm².

Propellers and radio ground plates

Regardless of its size, a propeller is not suitable as a grounding terminal for two reasons.

First, it is very difficult to make the necessary low-resistance electrical connection to the propeller shaft, and second, the primary conductor now runs horizontally through the boat.

The risk of side flashes within the boat, and through the hull to the water is increased.

Sailing in lightning: GRP hull, fairing filler and iron keel will have carried different voltages during the strike – hence this damage

An engine should never be included in the main (primary) conducting path to a grounding terminal.

On modern engines, sensitive electronic controls will be destroyed in a lightning strike, and on all engines, oil in bearings and between gears will create resistance and therefore considerable heat which is likely to result in internal damage.

However, as it is a large conductive object, the engine should be connected to the internal lightning protection system.

Internal lightning protection

On its way to ground, lightning causes considerable voltage differences in adjacent objects – up to hundreds of thousands of volts.

This applies to boats with a functioning external lightning protection system but without internal protection.

Although the lightning has been given a path to ground along which it will cause as little damage as possible, dangerous voltages can be generated elsewhere, resulting in arcing and side flashes, threatening the boat and crew, and destroying electronic equipment.

We prevent these damaging voltage differences from arising by connecting all substantial metal objects on the boat to a common grounding point.

One of the holy grails of marine photography – a direct lightning strike on a yacht’s mast. Credit: Apex

The grounding terminal is also wired to the common grounding point.

By tying all these circuits and objects together we hold them at a common voltage, preventing the build-up of voltage differences between them.

All conductive surfaces that might be touched at the same time, such as a backstay and a steering wheel, need to be held to the same voltage.

If the voltages are the same, there will be no arcing and no side flashes.

The bonding conductors in this internal LPS need to be stranded copper with a minimum size of 16mm².

Note that there can be bonding of the same object for corrosion prevention, lightning protection, and sometimes DC grounding.

We do not need three separate conductors.

Electronic Device Protection

With lightning protection systems, we need to distinguish electric circuit and people protection from device protection.

Even with an internal LPS, high induced voltages may occur on ungrounded conductors (such as DC positive) which will destroy any attached electronics.

A mechanism is needed to short high transient voltages to ground.

This is done with surge protection devices (SPD), also known as transient voltage surge suppressors (TVSS) or lightning arrestors.

Marine-specific SPDs are few in number and domestic models are not suitable for boats

In normal circumstances these devices are non-conductive, but if a specified voltage – the clamping voltage – is exceeded they divert the spike to ground.

There are levels of protection defined in various standards depending on the voltages and currents that can be handled, the speed with which this occurs, and other factors.

This is a highly technical subject for which it is advisable to seek professional support.

Most SPDs are designed for AC circuits.

When it comes to DC circuits there are far fewer choices available to boat owners although there are an increasing number for solar installations that may be appropriate.

There is no such thing as a lightning-proof boat, only a lightning-protected boat, and for this there needs to be a properly installed LPS.

Nigel Calder is a lifelong sailor and author of Boatowner’s Mechanical and Electrical Manual. He is involved in setting standards for leisure boats in the USA

Even so, in a major strike the forces involved are so colossal that no practical measures can be guaranteed to protect sensitive electronic equipment.

For this, protection can be provided with specialised surge protection devices (SPDs).

The chances of a direct lightning strike on a yacht are very small, and the further we are north or south of the equator, the smaller this chance becomes.

It’s likely your chances of receiving a direct lightning strike are very much higher on a golf course than at sea.

‘Bottle brush’-type lightning dissipators are claimed by sellers to make a boat invisible to lightning by bleeding off static electrical charge as it builds up.

The theory rests upon the concept that charged electrons from the surface of the earth can be made to congregate on a metal point, where the physical constraints caused by the geometry of the point will result in electrons being pushed off into the surrounding atmosphere via a ‘lightning dissipator’ that has not just one point, but many points.

It is worth noting that the concept has met with a storm of derision from many leading academics who have argued that the magnitude of the charge that can be dissipated by such a device is insignificant compared to that of both a cloud and individual lightning strikes.

It seems that the viable choices for lightning protection remain the LPS detailed above, your boatbuilder’s chosen system (if any), or taking one’s chances with nothing and the (reasonable) confidence that it’s possible to sail many times round the world with no protection and suffer no direct strikes.

Whichever way you go, it pays to stay off the golf course!

Enjoyed reading Sailing in lightning: how to keep your yacht safe?

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• Carbon Fiber Masts and Lightning: Myths, Assurances And Risks

Let’s start with the myths:

• If a carbon fibre mast gets struck by lightning it is toast, end of story.
• If a carbon fibre mast gets struck by lightning, there is no way to tell if it has been damaged or not, so it must be junked.

These two statements are right up there with “drop a penny in the bilge of an aluminum boat and it will burn through in a week”; in other words, rubbish.

I can say this because I have personally seen a carbon fibre mast that was struck by lightning and then pronounced undamaged by a large and reputable mast manufacturer using ultra-sound. And before anyone says that the manufacturer can’t be trusted, do you think that any manufacturer in their right mind would pronounce a mast safe, with the attendant liability, if they were not sure of their methodology?

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More Articles From Carbon Fibre Spars:

• The Benefits Of Carbon Fibre Masts
• Carbon Fibre Masts, Amateur Boat Design
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John and Phyllis and others, I came accros your expreience with the new carbon mast almost by a happy accident and am delighted with your comments. I am replacing the old aluminium mast (with in mast furling gear on my contest 50 this winter) with a new carbon mast from Hall Spars Holland. The original Alu mast is structurally OK (we hope to sell it and the sail) but I strongly suspect it has been killing the boat’s performance, not so much the speed but the motion of the boat. She pitches and rolls in a seaway especially with a following sea to what I regard as an alarming degree. The mast is 22m high and weighs without the sail, radar etc 560 Kg, so that’s over half a tonne (!!) whereas the new carbon mast (profile much reduced because the new mast has slab reefing) weighs 200 kg, so much more benefit than you achieved. Time will tell. We step the mast in February adn I will report back.

I have ordered a new sailboat (Luffe 37.09) built by a Danish boatyard with a carbon fibre mast and boom. Since the boat will be sailed in the Med initially they proposed that mast and boom must be varnished white above decks for decreasing heat issues caused by original black colour. Then they told me that the varnishing in white for that reason was a myth. Would you add some comments on that? Rumen

I would agree with Andrew, paint it white. The issue is not the carbon so much as the resin that holds it together. Over time the UV in sunlight will attack and weaken epoxy. White is probably best.

Hi Rumen and John. , congratulations on investing in carbon, wish I had insisted on this when I bought the boat. I had a black carbon mast on my racing boat which was clear varnished and used in the UK. Four years later the varnish had peeled off and the thin carbon fibres were coming off making it hazardous to climb the mast and no doubt affecting the strength of the mast. So a good painting is essential in my opinion and yes, very definitely have it painted white. I keep my cruiser in the Med now and it is so hot that a UV absorbing black mast would be a nightmare structurally and otherwise. I cannot recall seeing a black mast at all in any marina in the Med.

Hi John and Andrew,

Thanks for your replies. The manufacturer, Southern Spars claim that clear varnish only is OK.

Well, Southern Spars are a good outfit. And I guess clear coat is better than nothing, but still, it just stands to reason that white will reduce the temperature of the spar and stop more UV. I would go with white, same cost, longer lasting, more protection.

Thanks John, I appreciate your point. I will go for the white varnish above deck.

Hi Rumen, That’s what we did: white paint above deck, clear coat below, which is kind of cool because it shows off the carbon laminate, which, when well done, is quite beautiful and a bit like having a sculpture in the middle of your salon.

Also, by painting white, your spar will not scream :”carbon mast”, which can in turn touch off “must be a rich guy…double the invoice.”

Talking to the Dutch Hall soars guys they have some carbon masts that need no varnish at all but I would still go white for the reasons John gave….

would like to contact a manufacturer of carbon fiber masts

need 2 masts for cruising steel ketch

can you help thanks

I would recommend Hall Spars. They have plants in the USA and Europe.

How did you protect the carbon mast against lighting? You say you use both a lightning rod and a static dissipater. I am a little confused, I thought that was the same thing. So I guess I am asking some stupid questions…..

The static dissipater is the “furry” thing on top of the mast. Is the rod the wire that goes from the dissipater to the keel? If so, what kind of lightning rod do you use? And is it glued to the inside of the mast?

No, we don’t have both a dissipater and a rod. That is what Hall said, but I think that they may be wrong about that. Also, I’m not convinced about dissipaters. Therefore we have a lightning rod that is grounded to the hull through a #4 copper cable that runs the length of the mast.

You can lean more about lightning here .

I am very close to ordering my new mast. I think it will be a Hall mast.

They want to sell me a mast with a dissipater. They are telling me that they only use lightning rods for the really big boats, mast typical 45m high.

Did you order your mast with the lightning rod and the copper cable, ore did you mount it your self?

Twin keels and lightning

My mast are stepped on deck, but is connected to a support under deck that is metal. The keel frame is also metal, but the boat is a twin-keeler, so I guess I have a problem. If the lighting is going down my mast, the support tube (under deck) and in to the keel frame I guess it will go strait out of the hul and in to the water? It would not take a 1meter stepp to the right ore left to pass through one (ore both) of the keels. What do you think?

I’m sorry, I don’t have enough knowledge about lightning to give you an opinion on this stuff. All I can do it tell you what I have done, as above.

I would suggest that in the end your best bet is to take advice from your spar manufacturer, if for no other reason than if you don’t it might adversely affect your insurance cover in the case of a strike.

You will also find a lot of good information to help you in Matt’s article that I linked to above.

In a lightning strike “the rigging does the ”heavy lifting””

Any idea how synthetic rigging would perform in comparison with steel?

Also, how much might the weight of a substantial lightning conductor undermine the weight advantage of synthetic over steel standing rigging.

Intriguing ain’t it.

I would be fairly sure that synthetic rigging would not conduct well and therefore might be fried by a strike, but way too many variables to be sure. I guess the key point is that we want good conduction all the way to the sea, so if we have synthetic rigging then we need a conductor even more, regardless of weight.

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Lightning Protection: The Truth About Dissipators

About this time of year, when lightning strikes become frequent occurrences, we receive a good deal of mail asking about static dissipators such as the Lightning Master. These are the downside-up, wire-brush-like devices you see sprouting from antennas and rooftops in cities and towns, and more frequently, on sailboat masts. When these devices first appeared on the market, we did a fair amount of research to find out whether they realistically could be expected to spare a sailboat’s mast from a lightning strike. The following Special Report first appeared in the July 15, 1995 issue of Practical Sailor . Sailors also will be interested in reading about our discussion of conventional lightning protection systems in Getting a Charge Out of Lightning .

All sailors-except those who sail exclusively in the most northern but still liquid reaches of the Arctic Ocean, or most southern parts of the Antarctic Ocean-are well aware of lightning and its inherent risks. Lightning awareness generally takes one of two forms: (1) aware, concerned, resigned, do nothing or (2) aware, concerned, do something, and hope what was done will be more beneficial than harmful. In many ways, our ability to deal intelligently with lightning is little advanced from Benjamin Franklins approach. Most boats are built in compliance with the safety grounding and lightning protection recommendations of the American Boat and Yacht Council (ABYC). The highest mast will be well grounded to the sea through a copper wire of suitable size, which connects to a metal plate mounted on the hulls exterior surface. There may be a lightning protection air terminal mounted at the masthead. The terminal may take the form of a vertical spike with a sharp point or some more exotic shape and construction.

For years, a number of companies have started to aggressively market on-purpose lightning protection devices for use on boats. Although the devices appear to be little different from the forms that have been used on both aircraft and stationary constructions, some of the marketing claims have been rather innovative. Are these claims reasonable in light of what is known about lightning? Is the cost of protecting a vessel with one of these devices a good investment? Can you really placate Thor, the god of lightning?

How Lightning Occurs

First, let’s examine what we know about lightning. Lightning is a final result of the natural creation of an electrical charge imbalance in the Earths atmosphere. Simply put, the imbalance can occur due to the movement of the air, which like the movement of a person across a carpet, can cause electrical charges to be moved from one place to another. Imbalance in electrical charge causes a potential gradient to develop. This gradient can be measured and is usually expressed in volts per meter. The normal electric (E) field averages about 150 volts per meter. The field can exceed 1,000 volts per meter on a dry day. At this intensity, the potential difference from the head to the toe of a person 6 foot, 3 inches tall can reach 1,800 volts!

Since this is a static charge, it won’t electrocute anyone, but unfortunately, it also can’t be used to power the electrical consumers on a boat. The ability of the atmosphere to withstand or prevent a flow of electrical current when a voltage gradient exists can also be measured.

If, or when, the voltage gradient created by the charge imbalance exceeds the ability of the atmosphere to prevent a current flow, something will happen. In some cases, the charge will be dissipated harmlessly as a flow of ions. This flow may cause a visible affect under some conditions. Seen at night. St. Elmos Fire, an ethereal blue flamelike discharge, may be seen around any sharp points on the boat’s rig. In an aircraft, the blue glow may trail from wing tips and static discharge wicks (those round, pencil-like tubes seen protruding from the trailing edges of wings and control surfaces). An adventuresome pilot may be able to draw electrical arcs from the windscreen to his outstretched fingers. This type of electrical discharge won’t hurt you because the small electrical current moves through the surface of the skin, not through the internal organs of the body.

On some occasions, the build-up of charge gradient occurs very rapidly, so rapidly that little if any effective dissipation of the charge can occur before the stress applied to the air by the charge overcomes the ability of the air to resist. When this happens, the charge imbalance is relieved very quickly, by what we call lightning. Lightning is always occurring somewhere on the earth. The planet is always losing electrons. Although the current is very small, less than 3 millionths of an ampere per square kilometer, it amounts to an average global current flow of about 2,000 amperes. Nature balances this current flow by creating about 150 lightning strikes per second.

Lightning occurs both within the atmosphere, cloud-to-cloud lightning, and from the atmosphere to the earth, sky to ground lightning or the reverse, ground to sky discharge. Regardless of the direction of the lightning stroke, a great deal of energy is released as the electrical charge balance of the atmosphere-earth is restored. An average lightning strike consists of three strokes, with a peak current flow of 18,000 amperes for the first impulse and about half that amount of current flowing in the second and third strokes. Typically, each stroke is complete in about 20 millionths of a second. Once the lightning strike occurs, the air becomes a conductive plasma, with a temperature reaching 60,000 degrees. The heating makes the plasma luminous; in fact, it is brighter than the surface of the sun.

Measurements made of the current flow in the lightning strike show that 50 percent will have a first strike flow of at least 18,000 amperes (18 kiloamps, or kA), 10 percent will exceed 65 kA, and 1 percent will have a current flow over 140 kA. The largest current recorded was almost 400 kA.

Current flows of this magnitude are serious stuff and cannot be dealt with lightly.

The Risk to Structures

People who have boats and those who have towers or tall buildings share a common concern about lightning. Due to the altitude distribution of the air movement in the atmosphere that gives rise to the charge imbalance, things that are tall and stick up into the atmosphere are likely to be attractive targets as nature tries to rid itself of the charge imbalance. Since there are more tall towers than seriously tall boat masts, and since lightning-strike records are kept for these towers, we can use this data to ascertain the affect of tower height on attractiveness for lighting strikes.

The Westinghouse Co. obtained data for isolated, grounded towers or masts on level terrain, in a region that experiences 30 thunderstorm days per year. The number of strikes per tower or mast did not reach two until the height of the tower exceeded 500 feet. With a tower 1,000 feet high, the strike frequency was about nine. Towers more than 1,200 feet high were struck more than 20 times. Although the data may not be accurate for very small towers or masts, it appears that the chance of a typical 60-foot sailboat mast being hit will be quite close to, but clearly not zero. We know that there is always a chance of being hit by lightning; after all, people walking on beaches have been hit.

The ground wire, usually the topmost wire in an electrical power transmission line, is frequently hit. Trees are hit very often, sometimes exploding due to the instantaneous vaporization of moisture within the wood. Concern about lightning strikes on golf courses is sufficient to cause the Professional Golf Association to take special measures to ascertain the level of a threat of lightning and to stop play when the local electrical field strength and other indicators show a probability of lightning.

Charge Dissipation

Some people believe that by constantly discharging the charge build-up on an object, the magnitude of the charge imbalance can be controlled and kept to a level where a lightning strike will not occur. Continuous dissipation of static charge potentials is used in every electronics laboratory that works with sensitive integrated circuits and transistors. The workers wear wristbands of conductive material that are connected to the rooms electrical ground. Charges bleed off before they reach levels that might destroy the electronics.

Unfortunately, what works in a laboratory, with very modest static charge quantities, does not work in nature. Let’s look at the facts that govern the charge dissipation approach to undoing what Thor wants to do-blast us with a lightning bolt.

We can begin with some interesting evidence in nature. Trees have many thousands of reasonably sharp points. These points should operate somewhat like man-made charge dissipation devices. The evidence shows that trees, even small trees, are constantly being hit by lightning. Although trees are not terribly good conductors of electricity, they do in fact conduct to some extent, as witnessed by the lightning strikes they suffer. Suppose we substitute a carefully designed set of sharp points for the branches and twigs of the tree. We will make the sharp points of a material that conducts electricity very well, perhaps metal, or graphite (used in aircraft static wick systems). The idea is to take the electrostatically induced potential in the ground system and convey it to the sharp points where it can create ions in the air.

Sharp points create the greatest possible voltage gradient, enhancing the creation of ion flow. As the ions are created, they are supposed to be carried away by the wind, eliminating or greatly reducing the total potential difference, thereby reducing or eliminating the chance of our object being hit by lightning.

The problem with this approach is that the earth can supply a charge far faster than any set of discharge points can create ions. A bit of math will show that a carefully designed static discharge wick or brush can create a current, in an electrical field of 10,000 volts per meter, of 0.5 ampere. This is equivalent to a 20,000 ohm impedance (R=E/I: R=10,000/0.5 = 20,000). The impedance of a site on hard ground is typically 5 ohms. The ratio of the ability of the earth to supply a static charge is inversely proportional to the impedance of the conductor. In this example, the ratio of impedances is 20,000 : 0.05 = 4,000:1.

The earth can supply energy 4,000 times faster than the rate at which a static discharge brush can dissipate the energy! The impedance of saltwater is a great deal less, on the order of 0.1 ohms, making the theory of protection from use of static wicks even more suspect.

Another concept quoted by advocates of lightning prevention through the use of static discharge devices is that the wind will carry off the ions being released by the wicks or brushes. Not only will the wind-blown ions not prevent a strike, they may present a converse affect when there is no wind. In this case, they may migrate upward, making the air more conductive and possibly creating an attractive point of attachment for a step leader which is lurking above looking for a place to strike. Data indicates that step leaders, the precursor of the main lighting strike, don’t pick out a point of attachment until within about 150 feet of an object.

Scientific evidence of the behavior of the step leader indicates that it moves in steps about 150 feet long. This indicates that objects more than 150 feet above the surrounding terrain are more likely to be hit than those which are shorter (most sailboat masts). Until 1980, it was assumed that a grounded mast would provide protection against a direct lightning strike for all objects within a 45-degree cone whose apex was at the masthead. From that date the National Fire Protection Association has advocated that a different assumption be used (NFPA Code#78). This code recommendation assumes that a 96-percent protected volume exists adjacent to a grounded mast, with the boundary of the protected volume described by a curve having a radius of 150 feet (the length of one step in a step leader).

Makers of static discharge devices often quote evidence of many installations that once equipped, have never been hit by lightning. Unfortunately, these reports must be considered as anecdotal, not scientific proof of the value of the system. The fact is that the chances of a given mast or tower of the dimensions of a typical sailboat mast being hit by lightning are exceedingly small. The willingness of some makers of these systems (notably Island Technology, maker of No-Strike devices) to offer to pay the deductible amount on an insurance policy, or a fixed amount if there is no insurance coverage, is good financial accounting on their part rather than proof of the scientific value of their device.

For example, if you assume that the chances of an equipped vessel being hit by lightning are 1 in 1,000 (much higher than actual probability) and you charge purchasers as little as $10 more than normal for the product, you will have accumulated a $10,000 reserve from which to pay the $1,000 deductible amount on an insurance policy.

This income to cost ratio of 10:1 is somewhere between very good and wonderful. Given the price being charged for some of the devices, which offer to pay up to $1,000 toward the deductible in the event of a lightning strike, the ratio of income to probable cost for payout in the event of a lightning strike is more on the order of 100:1, or greater.

Recommended Practices

What should you do to protect your boat from lightning? The best advice available today is to follow the practices recommended by the ABYC for both lightning protection and grounding. Installation of a good lightning protection system wont hurt. If you like the idea and appearance of a particular kind of static discharge device, sharp points, brush or whatever, install it.

When in an active thunderstorm area, you may wish to have all personnel stay as far from shrouds and the mast as practical, and refrain from using electrical equipment. Some skippers may wish to disconnect electronic devices from all connections to the boat, power and antennas, although in the event of a direct strike, even this may not protect the increasingly sensitive solid-state devices used in this equipment.

And If You Play Golf…

The real risk from lightning appears to be greater for those who play golf than for sailors. The practice at most golf tournaments held in areas where lightning is common is to employ various weather monitoring systems to provide some advance warning of a coming storm or likelihood of lightning. A company appropriately called Thor Guard offers a lightning prediction system that monitors the electrostatic field in the nearby atmosphere. The system compares the monitored data with a stored data base and predicts the probability of a lightning hazard in an area up to 15 miles in radius from the monitor. This system is really not practical for use on a boat, although it could be used to provide warning for an area in which a small boat race was being sailed. It would appear reasonable that, with the very large amounts of money involved in delaying a major golf tournament due to the chance of lightning, static dissipation devices would be sprouting from the fields and woods if they could be shown to work.

The chances of being hit by lightning are very low. There is really nothing you can do to dissuade Thor if he takes a liking to your masthead. You might install an electrostatic field strength meter, or calibrate the hair on the back of your head. When the needle indicates a high enough field strength, or when your hair stands up straight enough, give everyone except the helmsman their favorite drink and invite them to watch the show.

For more on on board electrical systems, grounding, and lightning protection see our ebook Marine Electrical Systems – The Complete Series available in our online bookstore .

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35 comments.

I remember reading about this stuff from the Florida Lightning Research Laboratory back in about 2005. We were living on a Catalac 10M at the time and debating with a “licensed” Marine surveyor who thought the little whisk brush like devices were the Cat’s Meow. But even grounding the mast on the catamaran is questionable due to the bridge deck and high energy not liking to turn corners. In 10years cruising never heard a good answer. 🙁

When I was leading the design of an aircraft antenna for Inmarsat communications which was to mount under the fibreglass fairing at the top of the vertical stabilizer we were concerned about lightning strikes. We could not use the heavy aluminum straps used on nose radar domes as this would have degraded the performance of the antenna. We found that a strip of copper shim washers which were not touching each other and supplied as a self adhesive strip could provide lightning protection without interference with the antenna. I understood that this was something invented by a Boeing engineer. The theory was that at very high voltage the strip would be conductive enough to discharge the air near it so that lightning would not conduct near it.

watched a boat hit by lightening in a race. The strike took out the UHF antenna; twirling it like a baton. The boat was chasing us. When we returned to the clubhouse at the Bristol, RI yacht club, the captain was unaware his yacht had been struck. Taking down the mast revealed the entirety of the top of the mast work was melted. No injuries.

Does it make sense to store electronic devices like computers, tablets, or smart phones in the oven during a thunderstorm?

Theoretically, yes – Faraday cage.

yes, a magnetic pulse protection case

A particularly poor article with advice written with poor knowledge of the subject matter. Ion dissipators have been used in the broadcast antenna and aircraft manufacturing industries for decades. Are they bulletproof? Nothing is, however, your main argument seems to be that if it’s not bulletproof then they shouldn’t be used at all. A properly designed sailboat with grounding straps and ion dissipators will encounter far far less lightning strikes. It’s almost as if this article was written by a salesman who wished to increase his commissions. This article should be withdrawn!

Do you have ANY real-world data to support your terribly convoluted implication that ion dissipators reduce lightning strike frequency or even severity? Your reaction is just like that people give when they have a paradigm in their field that is being challenged and they can’t refute the challenge. FACT: The article addresses claims that are unsupported with conclusive evidence. Those claims are refuted to a varying degree with real-world examples suggesting dissipators do not add value as well as mathematically-based models that suggest they do not. FACT: You have offered *nothing* to support the notion that ion dissipators reduce strike frequency or even severity. Your haughty attitude is worth nothing in the quest for a common basis for agreement (a basis of commonly acceptable evidence and logical or probabilistic analysis).

I add that your insulting complaint about the author’s motivation actually makes no sense – it is inherently self-contradictory! It’s almost as if *your* comment “…was written by a salesman who wished to increase his commissions.” Your comment should be withdrawn! How would the author make money by *reducing* sales of an item that provides a so-called solution when there are not even other competing types of products to provide that solution.

Let’s add one final note. You seem to think longevity of use proves effectiveness. That’s a foolish belief. Casting spells was *and is still* used by people to protect themselves. Prayer is believed by *many if not most people* to be a protective method with statistically significant results no less! Toxic elixirs were believed to help heal people for millennia until proven otherwise. Items providing more specific protections have also been around for centuries and yet eventually proven to be useless or harmless. Particularly when money is to be made *or esteemed “expertise” to be had*, humans will promote beliefs that run counter to reality. Don’t presume such behavior is justified just because it persists. You are not a child – you know that. So take that to heart and stop acting like such motivators are not an influence on (and perhaps the ONLY reason for) the sales of ion dissipators.

Thanks for the great academic review. I guess many of us are really interested in the ‘practical’ (sounds familiar? :)) bottom line recommendations for sailboats, not so much for golf courses… And somehow the clear message got lost within the text; what works and to what level, the costs, other means of protection and damage prevention while cruising and at the dock/mooring.

The article seem to leave a void. I was reading it for the same info. Thanks for posting.

It seems clear to me that the take-away from this article is that ion dissipators lack justification beyond making some people money and being “security blankets” for customers (or worse, show-off items for fools). The author has *not* chosen to tell you what to do, but should any article really do that if the author trusts the audience to make the right choice for themselves (if maximally informed). Choice of action is your own responsibility.

This might sound a bit naive but does attaching heavy duty battery cables to the upper shrouds at the deck and letting them dangle in the water help dissipate a lightening strike to the top of the mast? Or, prevent one for that matter? I tried this while crossing the Tehuantepec in Southern Mexico, Pacific side, when I went through a lighten storm where lightening was hitting the water all around me at a rate of about once every second, believe it or not. It lasted for a good two hours. I was the only sailboat out there. Does anybody know if the cables might have made a difference, maybe by dispersing ions or something like that? Or, if hit by lightening, would the cables be able to direct the charge to the water? Thank you

I have heard the same thing and I do attach heavy duty cables to my shrouds and drag them in the water (shrug) no idea if it achieves anything as I’ve never been struck by lightning I figured it can’t hurt ! Or can it ?

20,000 : 0.05 = 4,000 : 1 ?? Um, maybe….. 400,000 : 1 ?

Otherwise, very informative article. Thx!

I think that 0.05 was supposed to be 5, so the 4,000 would be correct. Where would the 0.05 come from if it is not a mistake?

I agree the article left me hanging with no course to follow. How deadly are lightning strikes on sailboats? Should we just rely on insurance to replace damaged equipment? What steps can we take during a storm to protect life/property?

Steve not sure what protected your boat in that storm,,,,frightening . I am an engineer but no lightening expert.

Here is my lightening story. We have an Islander 30 MKII in an end slip at McKinley marina in Milwaukee. Our neighbor was a visiting catamaran from Africa about 45 feet long on the face dock across from our boat. The masts were about 30 feet apart. Prior to the storm I recall talking to the cat owner as he had a serious cable from the mast into the water. Said it was for lightening protection with a large copper plate in the water. That night his mast was hit by a lightening strike. The next morning we went to check things out. The strike destroyed everything electrical or electronic including appliances etc. on the catamaran. Melted portions of his masthead that rained down on his deck left burn marks. After hauling the cat there were hundred black soot holes at the waterline. All needed to be repaired. The only thing that happened to me was the circuit breaker on my boat was tripped. Breakers on the dock were tripped also. No electrical or electronic damage for me. Essentially the neighboring boat took a hit for me. The strike must have created quite an electromagnetic field to trip breakers. Got lucky on this one.

Your vessel might have even been contacted by a weaker branch of the same strike. Close-up views of lightning strikes show they can have multiple points of contact, with some channels much brighter (presumably carrying much more current than the dimmer/narrower ones).

Can a well-grounded mast actually attract a strike? Our 41′ Morgan O/I was anchored at Cape Lookout NC with more than a dozen others, our mast just average height but grounded to a bronze plate. We were the only boat hit, and the water under the hull boiled orange!

An experienced surveyor, who had seen a number of lightning-damaged boats in the course of his career and made note of the protection measures in place on each, said to me, “Bottom line, lightning’s gonna do what it wants.”

A couple of thoughts on boats and lightning and the lack of specific recommendations. Me; live in low lightning area, trailer sailor and amateur radio operator. I installed an outdoor antenna a year or so ago on the house. A child of the Midwest, I took lightning protection seriously. Found a bunch of info on line, some good and some,….well, less so.

Key things that stood out; + kinda like Descarte’s argument for believing in God. the liklihoods may be small, but the consequences can be grave. +there are maps of lightning liklihood out there on line + Electricity follows the path of least resistance. Lightning is so electrically huge that it will explore all possible paths. Provide the easiest, most direct path possible for a lightning strike to reach ground that guides the current away from people and sensitive gear. Here that meant two stranded 2/0 leads (about 3/8″ diameter) from the antenna bracket directly to individual ground grounds which were then “bonded” to three ground rods serving the house wiring with about 90+ feet of #4 solid copper (smaller diamater #6 meets code but, some of the literature recommended #4 to be on the safe side). The antenna coax where it enters the house in a metal junction box was separated from the jumper that attaches to the radio by a “lightning arrestor.” The arrestor and surrounding metal box are directly grounded (#4 solid copper) to one of the antenna rods located directly under the box. + the concept of path step distance; if I am standing outdoors close enough to a ground rod or down wire, and the antenna takes a hit, the current in the soil or the wire may be strong enough to kill simply by going up one of my feet and down the other or grounding through my body. See pictures of dead cattle standing next to a barb wire fence that was hit by lightning. If I am standing out on the wet hull of a sail boat and the mast takes a hit…..maybe the same would apply. Moral here; stay as isolated as possible from the paths lighting might follow. + more ground rods are better than fewer for disapating the current into the surrounding soil. How this translated into ground plates on boats, dunno, but more might be better than fewer there as well. +British and European lightning structural protection standards have been regarded as more robust than our NFPA standards. Dunno about boats, but might be worth investigating. +soils vary in their ability to absorb electrical current; probably the same holds with fresh vs salt water. Ground rods do corrode in the soil over time. Pouring salt around a ground rod increase electrical transfer to the soil and also decreases ground rod life. Not recommended. Better to add more ground rods. +if an electrical storm is on the way, and I happen to be on the premises, I disconnect the radio from its coax antenna lead _and_ its power source (two paths for lightning). Also, unplug the power source from the wall outlet. A surge protector might not block juice coming in on the ground wire. +I have not placed the radio in a microwave. That solution I have seen offered for EMP protection, provided that the power cord is cut off to avoid acting as an antenna for high voltage RF input.

That’s about all I can think of of terms of main points. My fellow hams do not use the same level of lightning protection, but seem to regard mine as along the lines of the way to do it. Good luck on coming with with systems for sailboats

Hope useful, Full sails, Ole

A couple of thoughts on boats and lightning and the lack of specific recommendations. Me; live in low lightning area, trailer sailor and amateur radio operator. I installed an UHF/VHF outdoor antenna a year or so ago on the house. A child of the Midwest, I took lightning protection seriously. Found a bunch of info on line, mostly good and some,….well, less so.

Key things that stood out; + kinda like Descarte’s argument for believing in God. the liklihoods may be small, but the consequences can be grave. +there are maps of lightning probabilities out there on line for land masses, perhaps also for the oceans + Electricity follows the path of least resistance. Lightning is so electrically huge that it will explore all possible paths. Provide the easiest, most direct path possible for a lightning strike to reach ground that guides the current away from people and sensitive gear. And even then, keep your fingers crossed. Here, that meant two stranded 2/0 leads (about 3/8″ diameter) from the antenna bracket directly to individual ground grounds which were then “bonded” to three ground rods serving the house wiring with about 90+ feet of #4 solid copper (smaller diameter #6 meets code but, some of the literature recommended #4 solid Cu to be on the safe side). The antenna coax where it enters the house in a metal junction box was separated from the jumper that attaches to the radio by a “lightning arrestor.” The arrestor and surrounding metal box are directly grounded (#4) to one of the antenna’s grounding rods located directly under the box. + the concept of path step distance; if I am standing outdoors close enough to a ground rod or down wire, and the antenna takes a hit, the current in the soil or the wire may be strong enough to kill simply by going up one of my feet and down the other or grounding through my body. See pictures of dead cattle standing next to a barb wire fence that was hit by lightning. If I am standing out on the wet hull of a sail boat and the mast takes a hit…..maybe the same would apply. Moral here; stay as isolated as possible from the paths lighting might follow. + more ground rods are better than fewer for disapating the current into the surrounding soil. How this translated into ground plates on boats, dunno, but there as well, more area might be better than less. +British and European lightning structural protection standards have been regarded as more robust than our NFPA standards. Dunno about boats, but might be worth investigating. +soils vary in their ability to absorb electrical current; probably the same holds with fresh vs salt water. Ground rods do corrode in the soil over time. Pouring salt around a ground rod increase electrical transfer to the soil and also decreases ground rod life. Not recommended. Better to add more ground rods. How lightning grounding plates on a salt water boat might interact with Zn anti-corrosion plates…..dunno. +if an electrical storm is on the way, and I happen to be on the premises, I disconnect the radio from its coax antenna lead _and_ its power source (two paths for lightning). Also, unplug the power source from the wall outlet. The surge protector might not block all those Amps coming in on the ground wire at high Voltage. +I have not placed the radio in a microwave. That solution I have seen offered for EMP protection, provided that the power cord (now an antenna) is cut off to isolate the metal case from high voltage RF input. Probably work for lightning as well.

That’s about all I can think of of terms of main points. My fellow local hams do not use the same level of lightning protection, but seem to regard mine as along the lines of the way to do it. Good luck on coming with with systems for sailboats

Last point; ground (earth) rods are recommended to be spaced horizontally at least 2x the length of the rod, to better maximize current transfer to soil (minimizing overlap of the electrical fields emanating from each rod). For standard 8 foot rods, that equates to 16 foot spacing. How that translates into size, shape and spacing of grounding structures on a boat electrically connecting to the surrounding water might be a useful question to explore. Again good luck on coming up with systems for sailboats.

Thank you. Best explanation I’ve read about lightning. Shame there’s no definitive answer, but I think there’s not much we can do about lightning. Been through Tehuantepec at the wrong time of year (July), bolts everywhere, but never hit. My best story was in Costa Rica, early ’70s, aboard our Lodestar Trimaran ketch, wooden masts with S.S. masthead fittings, lightning all around, and close, and I hear a buzzing sound, look up and we have a glowing ball on both mastheads. Saint Elmo’s Fire. Basketball size on the main and grapefruit on the mizzen. Every close strike made them flare up and buzz louder, then they would return to “simmer”. This went on for over an hour. Finally, everything died down and they went out. It was extraordinary and colorful to watch, but I was pretty nervous steering with our S.S. tiller.

High altitude mountain climbers are supposed to try and get off the peaks before the lightening begins; usually by noon. If you get caught in a storm with lightening and can’t get down below treeline or into some type of depression, you are taught to keep away from your ice ax and for sure don’t leave it attached to your pack with the spike pointing up. Then crouch down as low as possible with legs and boots touching each other so you don’t have as convenient a way for the strike to go across your heart from one leg to the other. Maintain a low crouch and only touch the ground with the two boots together. No hands. Then between strikes, run down-hill like the devil is after you.

I don’t think that would work on my Catalina 27 though.

As a life long sailor, golfer, and electrical engineer who has a more than average understanding of lightning and potential protection from it, here is the 10% you need to know as a sailor:

– Mast top static dissipaters are worthless and, as the article points out, could have a negative effect. – Proper bonding of your mast and shrouds to a hull mounted grounding plate is a worthwhile project. With that said, a large strike will overwhelm even a well designed and installed grounding system.

This has usually been an academic subject as most of my sailing has been done is areas not prone to lightning storms. However, on 8/15/2020 we got caught in the most hellacious lightning storm I have ever been in off the coast of Big Sur after leaving Carmel, CA. It is the same storm that created the massive wildfires still ravaging northern CA. Had the most extreme lighting bolt I saw that night make a direct hit our boat, a 36′ cutter, it would have likely destroyed our boat and killed the crew. The good news is the odds of getting hit in a bad lightning storm are likely better than the 1 in 1,000 actuarial odds per the insurance companies but are probably not 1 in a million either.

Finally, this is as well written and article on this subject that I have seen.

To the catamaran on fresh water, sorry, fresh water isn’t conductive enough for grounding. Salt water is an electrolyte however. https://nemasail.org/news/7279551

reading all of this it made me question why proper grounding should be a positive thing to do ?! …since electricity always follows the path of least resistance, why should I create a perfect path to ground and even attract a lighting? within a storm cloud negativ electrons are seperated from positive charged ions. The lightning is a visible path of current. On the boat, it is suggested to insulate yourself … so why not insulate the boat? instead of creating a path to ground? Or why not even give the mast and rigging a low positive charge on purpose? As far as I could understand, St. Elmo’s fire is a visible corona discharge. A positive charged object leaking charge. That means if you see St. Elmo’s fire on your masthead you are protected ?, since your equipment is not negative charged and the lighting would not be drawn into it? I might have completely wrong, but I could not find proper answers, yet. Most of these articles repeat the same stuff. I found the comments here more interesting.

Interesting.

But are you ignoring voltage gradient in this analysis? The voltage difference between the source (the cloud) and the sea creates a volts/metre gradient. Your ion dissipation doesn’t have to reduce the charge to the voltage of the cloud. It just has to reduce the voltage by more than the voltage gradient over the height of the mast, to make the top of the mast appear less polarised than the sea around it, (or less polarised than the boat anchored 100m away). It just has to do a better job than the dissipation of the surroundings. Happy to be corrected if I’m missing something.

I suspect that dissipators work better on catamarans as the masts swing less, and don’t move out of their own ion cloud. Am I visualising this right?

Hi, it’s sad this marketing pseudoscience and I am glad of this well documented article. It’s sad that we normalize this situation and keep using tension masts or sloops and rely in insurance, because this is a real problem for blue water sailing and so this must be one of the main factors in sailboat design.

1st. boats must be multisail as ketches are, using light freestanding masts to me removed in case of electric storm, also can be used some sort of small thick rounded mast with large boom as sort of wide short sail in that scenario. 2nd. all electric equipment must be located in a magnetic pulse protection case (with spare parts of sensors to be replaced), because this is the real problem with in situ strikes and nearby strikes, and even fireworks.

this risk is real and im glad is less frequent than thought

also, the boat could use a bow freestanding mast with a ground plate in the bow to avoid boat and personal damage

Not to be contrary, but charge dissipation DOES work as a mitigation. Looking at it slightly differently – if the earth were a perfectly conducting sphere, the probability of a lightning strike would be equal everywhere. Add hills, mountains, towers, buildings, trees, hay stacks and other objects on the surface and each accumulates charge build-ups over the perfectly conducting earth. The idea is to put an “air terminal” on the object you want to protect to lower the probability of a strike – not to eliminate it which would be nearly impossible. In other words, drop the charge difference from your tower or mast relative to another location or object. This is a lot like using camouflage to hide objects from the air. An extension of this is used in power plant and substations where there are aerial lines strung from towers above the working of the plant to “pull away” the potential strike from the critical components. Also a taller object well grounded yields a so called “zone of protection” which is roughly a 45 degree angle from the top of the object to the ground. Things inside are less likely (there’s that probability word again) to suffer a strike or damage. In grounding a number of communications installations on mountain tops for commercial and government installations, the so called “bottle brush” type of dissipation has proven (through experience) the best. A lightning rod must be continually sharpened to dissipate. If not, it becomes dull and accumulates charge rather than dissipates it. The bottle brush has around a hundred stainless steel points which are thin and dissipate well – and last over time. The real key, however, is not the bottle brush, lightning rod or other dissipation device, it is the construction and connections to the Earth Electrode Subsystem of which there are many types and rules – Another topic.

A joke i like to tell: with sailors you can talk about religion and politics but not about anchoring or lightning preotection… We have been struck four times on our 38′ catamaran. Two times within 2 minutes, these strikes nearly totaled the boat (in insurance terms) as it wiped everything electric, from electronics to engine wiring harnesses and caused fiberglass damage. The third time it “just” took out the electronics, the fourth the inverter. What we learned: we have over 50,000 miles and twenty years onboard and have sailed or been at anchor thru many a breath taking lightning storm. All of the lightning strikes have occured at docks while hooked to shore power! The fourth strike hit our neighbors mast who had a dissapator talked about in the article. He had, ironically, told me the day before how it had kept him safe for two years… Strikes 1&2 hit us rather than the boat next to us whick had a 10′ taller mast. Strike 1,2&3 had us the farthest boat out on the pier. Insurance companies tell us the order of most likely to least likely to be struck: sailing trimarans, sailing catamarans, monohaul sailboats, power boats. It all seems to come down to how much water (and i am talking salt water) you cover. While properly connected metals are important for corrosion resistance, grounding a mast properly will not save your boat in a direct strike for several reasons: First off, as mentioned in other replies, it is extremly difficult to do. Second, the amount of power can easily overcome any grounding system, third, the emp is going to wipe sensitive things out anyway. Long and short of it is you wither need insurance or a boat with no electronics, which, btw, is what we had when we first started sailing…

The choice ground or no ground. Controlled invited strike or uninvited catastrophic strike due to arc jumping. I would like for people that have experienced strikes to specify if they had lightning protection or not to compare results. Let me confuse the reader even more: in the pouring rain the lightning can travel around lightning protection from the mast down wetted surfaces to the vessels water line. That may explain water line damage. During a storm I hoist a thawed Turkey and an old two way radio to the mast head, some say it satisfies Thor.

I witnessed my own boat being struck with lightning while moored in front of my home. 34′ sailboat in fresh water, without grounding, keel stepped mast, external lead fin keel epoxy coated. I was standing at the window watching the storm pass when BOOM and I saw a cascade of white hot sparks from the masthead as the windex and VHF areal were vaporized. Waited for the storm to pass and rowed out to inspect the damage and found nothing! Electronics worked, even the radio fired up but obviously would not transmit or receive. Hauled the boat later in the week and found about one hundred little “craters” on the bottom that were the exit points of the strike. The craters only were as deep as the gelcoat and part way in to the mat skin coat. Ground them all out and filled, faired, and painted them. All good after replacing the windex and VHF… Lucky I guess…

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How Likely Is Your Boat To Be Struck By Lightning

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Spring and early summer are the most active times for thunder and lightning storms. Here's the good news and the bad.

Photo: David Keen

According to reports from our BoatUS Marine Insurance claim files, the odds of your boat being struck by lightning in any year are about one in 1,000. Some states, such as Idaho, have no lightning claims (no surprise). But for those of you with boats in Florida, nobody has to tell you that the odds there are greater. Much greater.

Thirty-three percent of all lightning claims are from the Sunshine State, and the strike rate there is 3.3 boats per 1,000. Not surprisingly, the majority of strikes are on sailboats (four per 1,000), but powerboats get struck also (five per 10,000). Trawlers have the highest rate for powerboats (two per 1,000), and lightning has struck houseboats, bass boats, and even PWCs. Lightning-strike repairs tend to be expensive and time-consuming, but there are things you can do to lessen the damage after a strike.

You Can Run, But You Can't Hide

Volumes have been written about methods to mitigate damage or even avert a lightning strike. Lightning, however, doesn't seem to read them. As an example, one boat, fitted with a popular "fuzzy" static dissipater at the top of the mast, was struck twice in one year. Ironically, the second time the bolt hit the dissipater, it happened even though the VHF antenna right next to it was higher. Lightning is unpredictable. While you can mitigate the damage from a lightning strike, there is nothing you can do to prevent one. So here we'll focus on what to do if your boat is hit.

The Extent Of Damage Isn't Immediately Apparent

The first thing you should do if your boat is struck is call your insurance company and get your boat short-hauled as quickly as possible for a quick hull assessment. The reason is that when lightning exits your boat, it can leave via a thru-hull fitting or even through the hull itself. Even if the force of the bolt doesn't blow out a thru-hull or cause hull damage, it may cause a gradual leak that could go unnoticed and sink your boat. As part of its "sue and labor" provision, BoatUS Marine Insurance will pay to have your boat short-hauled to check for damage. The short-haul is not subject to a deductible.

Damage Is Determined By How The Strike Exits

In a properly bonded system that follows American Boat & Yacht Council standards, the strike should follow a low-resistance path to a boat's keel or an installed grounding plate, though few boats are equipped this way from the factory. While no two lightning strikes are exactly alike, examining a typical claim can shed some light on the possible damages your boat might have if it's ever struck; some may not even have crossed your mind. Example: Priority , a 33-foot sailboat, was struck in North Carolina during a July thunderstorm. Sailboats are nearly always struck on the mast — and this one was no exception. A damaged or missing VHF antenna is typically the first sign that an unattended boat was struck. Sometimes bits of a melted antenna are found on the deck.

It's no surprise that electrical devices are susceptible to strikes; NOAA estimates a strike contains around 30,000,000 volts, and a quick zap to a 12-volt device will certainly destroy it. But lightning is like horseshoes: "Close" counts. There can sometimes be collateral damage when a nearby boat gets hit, either the result of the lightning's powerful electromagnetic field or the current induced by the field running through the boat's shore-power cord. This can create strange problems; some electronics may work fine, others that are adjacent might not, and still others may only work partially. In some cases, compasses have been off by 100 degrees.

Lightning strikes can cause hull damage. If your boat has been struck, have it hauled to inspect for damage. (Photo: BoatUS Marine Insurance)

In one instance, the owner of a 28-foot sailboat noticed an amber LED on his battery charger that he'd never seen lit before, and his depth sounder had quit working. He couldn't figure out what had happened until his neighbor told him his boat had been struck. On another boat moored next to a struck boat, the compass readings were 50 degrees off and slowly returned to normal after a few weeks. But a direct hit usually causes more obvious and substantial damage.

When a boat gets struck, lightning is trying to find its way to ground, typically the water around and under the boat. When a sailboat like Priority gets struck, one of the paths the lightning takes is down the mast; typically, anything that happens to be close by on the way down can be destroyed: wind instruments, TV antennas, radar, lights, and so on.

Fortunately, aluminum is a very good conductor and allows the strike free passage. However, wood and carbon-fiber masts can get damaged because neither one is a good conductor. Thankfully, damage to the rigging is rare. Though mast-mounted components are the most likely to be destroyed, anything on the boat that is electronic can be damaged. As a general rule, if the equipment works OK after the boat was struck, it probably wasn't damaged; it's unusual for electronics to fail months later.

Often the first sign owners have that their boat was struck is that some of the boat's electronics don't work. Look for fuse failures, and if you have more than a couple of blown fuses, look to lightning as a possible cause. Powerboats are typically struck on the VHF antenna or bimini top, and though electronics are often destroyed, passengers are fortunately rarely injured. Sometimes, however, the engine electrical system is damaged. This underscores the need for nonelectronic signaling devices, such as flares, in case your boat is struck at sea and is taking on water or, worse, if someone is injured.

Lightning Can Be Brutal To Fiberglass

In the case of Priority , the lightning traveled down the mast in addition to the VHF coaxial cable. The cable had been disconnected and was resting against the hull inside the boat. When the strike exited the cable, it had no easy way to get to the water. After traveling a quarter of a mile through air, lightning has no trouble going through a fiberglass hull, and this is exactly what it did, blowing a 3-inch hole on the way. Fortunately, the hole was above the waterline, and the boat was saved from sinking.

Powerboats are also susceptible to hull damage and are less likely to have been fitted with a lightning-protection system. Fortunately, the strike usually exits the boat through the props and rudders, and aside from damage to the bottom paint, the running gear is not often damaged (although electronic engine controls sometimes are). Need another good reason to replace a leaking fuel tank? A 25-foot fishing boat with a small amount of fuel in the bilge exploded at the dock when it was struck, sending the contents of the boat's cockpit nearly 100 feet away. Rarely, the claims files show that lightning enters a boat's electrical system and creates enough havoc to start a fire.

Strike By Type Of Boat

Look for minor damage.

One component that is often destroyed is a ground fault circuit interrupter (GFCI). This can easily be overlooked after a strike. Though it may still power appliances, the protection circuit is often nonfunctional. A GFCI can be easily checked by pushing the test button on the cover. Other small items to check are handheld radios and GPS, bilge pumps, inverters, lights, and fans. It should be noted that lightning is fickle and boat damage varies enormously; one owner saw his boat struck on the mast and yet none of the electronics were damaged. The only evidence the surveyor could find of the strike was a blackened area on the masthead.

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Charles Fort

Contributing Editor, BoatUS Magazine

Charles Fort is BoatUS Magazine's West Coast Editor. He often writes local news items for BoatUS Magazine's Waypoints column and contributes to Reports, in-depth tech features in every issue written to help readers avoid accidental damage to their boats. He is a member of the National Association of Marine Surveyors, he's on ABYC tech committees, and has a 100-ton U.S. Coast Guard license. He lives in California.

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An approach to a modern sailboat lightning protection system

We were lucky when we were struck by lightning on our small 35’ GRP cruising sailing boat in Turkey in 2013, but without an LPS. All the plastic and some of the metal gear at the top of the mast exploded (see photo below) and simultaneously the headlining in the saloon exploded downwards with a loud bang. So much smoke that we initially thought we were on fire; but my wife and I survived unscathed to tell the tale.

The most likely discharge exit was through the propeller shaft, but practically all electronics were violently destroyed and, as an electrical and electronic engineer, my assessment for our insurance claim afterwards showed that most devices had experienced severe arcing with small electronic components having exploded internally (see photo below).

An lightning protection system is a bonding, grounding and shielding arrangement made of four distinct parts: Air terminals, down conductors, a low-impedance ground system and sideflash protection.

The best lightning protection system cannot guarantee personal protection, or protection from damage to sensitive electronic equipment. Also it is not a lightning prevention system. I knew the private owner of one large blue water catamaran which has been struck three times in its life and it is not an old boat. Fortunately no one was hurt on any occasion, but many electronic systems on that complex boat were effected and had to be replaced on each occasion. Unfortunately catamarans are many times more likely to be struck than mono-hulls and records in the USA, where certain locations are particularly prone to electrical storms (e.g. Florida where boat ownership is high), show that mono-hull sailing boats are about 25 times more likely to be struck than motoryachts.

Lightning is very hard to study and to accurately predict its behaviour is almost impossible, but it is driven by the simple fact that a massive potential difference (voltage) exists between the highly charged clouds of a brewing thunderstorm and the surface of the Mother Earth. Eventually, a path is found through the atmosphere down to ground for some of the accumulated charge to discharge and the creation of a discharge path first requires the creation of so called ‘streamers’ [1],[2]. Bear in mind that air breaks down at 3 million Volts per metre, and you get some inkling of the enormous voltage differences involved.

In the middle of a large body of water, with your sailing yacht in it, the top of the mast, being the highest point around, looks like a handy point to discharge through. So the LPS is designed to control the first point of discharge and then make the onward path to ‘ground’ – in this case the sea – as direct as possible and capable of conducting very high currents for a very short time during the discharge.

In 2006, the American Boat and Yacht Council (ABYC) technical information report TE-4 [3], [4] recommended the following:-

• lightning protection system conductors must be straight and direct and capable of handling high currents. The main ‘down’ conductor is recommended to be 4AWG, or 25mm2 in European sizing; see diagram.

• A large enough area ground must be provided between the vessel and the water to offer an adequately low resistance path (ABYC recommends 1sq.ft. {0.1m2} in salt water; much larger in fresh water. NB this is not adequate for acting as the SSB counterpoise). Metal-hulled vessels naturally offer a large ground contact area with the sea, but the connection between the hull and all other electrical systems needs careful consideration.

• Heavy metal objects such as fuel tanks and engines must be bonded to the ground bonding arrangement to reduce the risk of ‘side flashing’ where the lightning literally can jump from one conductor to another, seemingly better path. Similarly, it can jump out of corners in cabling, so if bends must be made, then they should not be more than 90° and with as large a bend radius as possible.

The basic arrangement is as depicted in the diagram, where the ‘air terminal’ is a rounded end (circled in photo) metal wand mounted at the top of the mast to ‘attract’ lightning to it and, most importantly, to stand at least 6” (15cm) higher than anything else e.g. above the VHF or other antenna. Providing the air terminal is securely electrically bonded, presenting a high surface contact area, low resistance path to an aluminium mast, the mast itself can be used as the down conductor at least to the deck or keel, depending on where the mast is stepped. In the case of wooden, or carbon composite masts they present too high electrical resistance and a 4AWG cable must be run straight down the mast as the main down conductor. From the bottom of the aluminium mast or down conductor, the 4AWG onward path needs to be as direct and short as possible to the ground plate, or the metal hull.

It is actually better to leave through-hull metal fittings electrically isolated if they are already insulated from the rest of the boat by dint of their attached rubber or plastic hoses and their insulating mounting plates – decent quality bronze alloy seacocks and engine intake strainers will not unduly corrode if left submerged for extended periods of time without needing connecting to the vessel’s earth bonding. However, in the US it is more normal to bond everything metal below the waterline, use a tinned copper bus bar running the necessary length of the vessel, above any bilge water level, to connect each through-hull fitting to, which is then connected at one point only to the main grounding route out of the boat. This bonding arrangement is gaining in popularity outside the US with consideration of a lightning protection system.

Note in the diagram that all tie-ins, including fore- and back-stay (unless insulated) must use at least 6AWG (16mm2 European) cable. All large metal objects within 6ft (2m) of the lightning down path also need tying in with 6AWG (16mm2) cable. Examples are metal fuel tanks, main engines (despite them usually already being connected to the water via their prop shaft) and generators; this is to minimize the risk of ‘side flashing’ where lighting can literally jump from conductor to metal object, looking for a better path to ground, even if one does not exist.

In considering of the creation of a ground plate of sufficient size, a metal hulled vessel is ideal, but nevertheless only one electrical connection point to the hull should be made from the main 4AWG down conductor. This same point should have all the other earth bonding made to it alone. The DC main negative bus in turn should be connected to the earth bonding in only one place, though European boats generally have their DC system isolated from any bonding system to discourage DC earth faults, the US differs in this respect, preferring direct bonding. One solution to this dilemma is to use a suitably rated surge capacitor between the DC negative busbars and the bonding system for the LPS. In the case of a non-metal hulled sailing vessel, the attraction of using the keel as a discharge point should be resisted as it is in contact with the water some distance below the surface where already a lot is going on with respect to charge balancing, so an alternative point is likely to be sought out by the discharge, nearer the surface. It seemed clear to our very experienced (and ancient) marine insurance surveyor that, during our own strike in Turkey, the discharge was out through the propeller shaft.

So far, so good, but recent thinking and good practice [5],[6] has modified the above ideas to take into consideration the danger of side flashing much more. A side flash is an uncontrolled spark that carries current to the water and can do extensive damage to hulls and equipment. The good practice and standards for a lightning protection system relating to marine situations, such as they exist (see NFPA 780, latest version, especially chapter 8, ‘Protection for Watercraft’, [7]) are tending to treat a boat more and more like a building to exploit those well tried and tested techniques used in a land based situation. Rather than a ‘cone’ below the air terminal, the ‘zone of protection’ is now more reliably envisaged to be formed from a ‘rolling sphere’ of 30m radius, as shown below for a larger yacht [7],[8]:-

Diagram of Boat with Masts in Excess of 15 m (50 ft) Above the Water; Protection Based on Lightning Strike Distance of 30 m (100 ft).

With a large building, the down conductors from the various air terminals run down the outside of the building to a number of grounding stakes; not so with a yacht where, as we have described, we’ve now concentrated the discharge right in the middle of the boat, where the danger of side flashing into other metal parts is very real; if these parts are not bonded and protected by a properly designed, low impedance path there’s are very real further danger of the side flash finding its way onwards and out through the side of the boat to the surrounding water surface. This has indeed been experienced by an American friend of mine on a high-tech, all carbon racing sailing boat on its way back to Newport, which after being unavoidably struck several times in a violent storm, put in to New York and immediately hauled to find literally a thousand or more tiny holes around the waterline when the discharge had exited! Apparently lightning does not always take the straightest path to the water, but rather has an affinity for the waterline.

The latest version of this NFPA 780 standard recognises this danger and, in a departure from the older versions, provides for multiple grounding terminals to provide the shortest path to the surrounding water surface. These ‘supplemental grounding electrodes’ conduct lightning current into the water in addition to that conducted by a main ground plate. The new standard provides for a continuous conducting loop outboard of crewed areas, wiring and electronics. Placing the loop conductor well above the waterline, outboard, and with grounding terminals below it retains the advantages of an equalization bus, whilst correcting for its weakness with side flashes having nowhere else otherwise to go.

Protection of electronic equipment by a hermetic system on larger yachts

So much electronic equipment on board a yacht struck by lightning is very susceptible to permanent damage. The only safe way to fully protect electronic equipment is to have it completely disconnected from all other circuits when thunder and lightning are nearby, and I still to this day do that as much as possible, but how practical is complete protection really?

A recent idea I had whilst discussing the problem with a 30m ketch owner may have some merit, and I call it a ‘hermetic system’, so suggesting that it is sealed from the outside world: If the most critical and/or sensitive electronic equipment can be enclosed within its own quite separate power and cabling set, separate from the rest of the boat’s electrical and electronic wiring, then it is possible that it could be saved in the event of a lightning strike. One way to do this would be to run all those systems required to be protected effectively off an Uninterruptable Power Supply (UPS), powered from the AC bus (via the generator), then down converted to the necessary 24/12VDC electronics supply. In the event of a lightning storm, all AC connections to the UPS and any signals, power or ground returns outside the hermetic system must be open circuited by large clearance contactors. The electronics contained within the hermetic system can still continue to operate, for a limited time (depending on the capacity of the UPS batteries) and further choices can be made about what to shut down within the hermetic system to extend the battery life, leaving for example just the absolute minimum electronics to continue to safely navigate e.g. Depth, GPS, Chartplotter. Very careful consideration must be given to cable runs.

The VHF antenna on the main mast may be protected by a surge arrestor from one of several suppliers e.g. www.nexteklightning.com. No guarantee is likely to the effectiveness of this as a protection device in all cases of lightning strike and the manufacturers should be consulted for further information.

I certainly now resort to the marvel of a GPS chart plotter on my mobile phone when there’s a nasty electrical storm about and I’m out at sea! References: –

1. Top 10 best lightning strikes (USA) by Pecos Hank, with rare photo of an upward streamer. 2. http://marinelightning.com/index_files/SFMechanism.gif for a graphic showing the formation of negative streamers 3. ABYC (US) technical report TP-4 “Lightning Protection”. 4. Nigel Calder – “Boatowner’s Mechanical and Electrical Manual: How to Maintain, Repair, and Improve Your Boat’s Essential Systems” 5. “Complexities of Marine Lightning Protection”, By Ron Brewer, EMC/ESD Consultant, April 2011 6. “A New Concept for Lightning Protection of Boats – Protect a Boat like a Building” Ewen M. Thomson, Ph.D.; published in the October 2007 edition of Exchange 7. National Fire Protection Association (US) document NFPA 780-2014 “Standard for the Installation of Lightning Protection Systems” – see especially chapter 8 ‘Protection for Water craft’. 8. “Evaluation of Rolling Sphere Method Using Leader Potential Concept – A Case Study” P.Y. Okyere, Ph.D & *George Eduful – Proceedings of The 2006 IJME – INTERTECH Conference

Feature article written by Andy Ridyard. Andy Ridyard has been a professional electrical and electronics engineer for more than 35 years and started SeaSystems in 2008. His business is dedicated to providing troubleshooting, repair and installation services to superyachts internationally, specialising in controls and instrumentation. He lives with his wife in Falmouth, UK, but works mostly in the Mediterranean. SeaSystems has fixed countless intractable problems with marine control systems, marine electronics, Programmable Logic Controllers (PLCs) and marine electrical systems. For more information visit SeaSystems.biz .

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Yachting World

• Digital Edition

Expert sailing advice: How to handle a lightning strike on board

• August 21, 2019

Pip Hare shares advice from sailors who have experienced a lightning strike on how to avoid getting hit by an electrical storm

The 2015 Volvo Ocean Race encountered electrical storms. Credit: Brian Carlin / Team Vestas Wind

Lightning is the thing that scares me the most at sea. Having never experienced a lightning strike I think this is mostly a fear of the unknown, coupled with a sense of helplessness.

My lightning strategy has always been to sail in the opposite direction and hope for the best. The following is a combination of my own practice and observations from sailors who’ve experienced a lightning strike first-hand.

Avoiding lightning

Thunderstorms are created in conditions where there is great instability between the upper and the lower layers of the atmosphere. Typically, thunderstorms follow an extended period of warm, still weather , but lightning can also form along very active frontal systems – this tends to follow a sustained period of average pressure, with little gradient breeze when the new front moves in quickly.

Forecasters can predict where there will be increased potential for lightning to form, but not its actual occurrence or exact location.

Specialist forecast models such as the CAPE (convective available potential energy) and the LI (lifted index) show storm potential by highlighting areas of atmospheric instability.

CAPE and LI forecasts are available via specialist weather sites and CAPE GRIBs can be obtained through some providers. Satellite images can also be useful for spotting intense areas of cumulonimbus clouds.

If planning a sailing voyage in areas where lightning could be expected, include a CAPE forecast in your daily GRIB run.

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Flashes on the horizon

If you get caught out or have to sail through an area where electrical storms are expected, it’s important to prepare for all the weather a thunderstorm can dish out, not just lightning.

Thunder claps can be heard for around 25 miles, so if the sky on the other side of the horizon is alive with light but you can hear no noise then stay vigilant but don’t panic – the storm is still a way off. Keep moving.

Keep a 360° look-out: due to the immense height of thunderclouds they are pushed along by upper atmosphere wind, not the sea-level breeze. This makes it difficult to predict which way a cloud is moving, they can sneak up behind you while you are sailing upwind. The best way to track thunderclouds is using the radar or a hand-bearing compass.

Prepare for a squall: wind associated with thunderclouds can reach in excess of 40-90 knots in a matter of seconds, this will often be combined with torrential rain and drastically reduced visibility. If there’s lightning around it’s best to keep on-watch crew in the cockpit so make sure you reef early.

Preparing for a strike

Lightning can strike up to ten miles away from the cloud that generated it. Just because you are in the midst of a thunderstorm doesn’t mean you will get hit – I’ve spoken to two sailors who reported lightning striking the water next to their boat but not touching them.

Others that were struck reported varying damage to electrical equipment and none experienced structural damage or fire. Here are some of their recommendations:

• Unplug all masthead units, including wind instruments and VHF antennas and ensure ends of leads are kept apart to avoid arcing.
• As the storm gets closer turn off all electronics – modern kit has increasingly efficient internal protection, but manufacturers still advise turning it off.
• Take a fix and plot it on a paper chart. Update your log using dead reckoning.
• Avoid touching metal around the boat, such as shrouds and guardrails.
• A nearby strike will be blindingly bright. Sit in the cockpit until your night vision returns.
• Expect masthead units, VHF antennas and lights to be destroyed, so make sure you carry a good quality spare VHF antenna.
• Fluxgate compasses can lose calibration following a strike. Check all electronic compass readings with a handheld compass.

Maximising protection

By providing a direct route ‘to ground’ down which the lightning may conduct you may be able to minimise damage.

Among my small sample of interviewees, only one had a lightning protection system: this was a sloop with a deck-stepped mast on which the chainplates were bonded to the keel bolts. The masthead unit on this boat was still totally destroyed by the strike but the remaining electronics suffered no ill effects. The same sailor had experienced a strike two years earlier with no extra protection installed – in that instance all electronics were destroyed.

The remaining sailors were all in boats of less than ten years old and reported varying degrees of damage to electronics and 100% destruction of masthead units.

The simplest protection system is bonding an aluminium mast to the keel bolts. On a keel-stepped mast this is easily done as the mast heel and keel bolts are close to each other. For deck-stepped masts this can be achieved by running an adequately sized cable through the deck head and down a bulkhead or supporting pillar.

Most modern boats have the mast bonded to the keel by manufacturers – if you’re not sure lift the soleboards to check. Masts made of less conductive materials such as carbon would require a conductor cable as well.

Air terminals at least six inches higher than any antennas at the top of your mast may save your masthead units. There is also considerable debate over the need for dedicated grounding plates – this appears to be more relevant to older boats as none of my interviewees suffered ill effects through grounding to the keel bolts.

Faraday cage

There is a theory that the oven on a yacht can act as a Faraday cage, protecting anything inside it from the effects of electrostatic discharge (ESD). Handheld or portable electronics can be temporarily placed inside a metal oven to protect them during a storm.

I have no conclusive evidence this works, but I’ve always done it, reckoning it can’t do any harm – just remember to take them out before dinner!

Return to Peterson Cutter Lightning Protection Page

How Often Do Sailboats Get Struck by Lightning?

Table of Contents

1. Introduction

2. Understanding Lightning Strikes

2.1 what causes lightning.

Lightning is a natural electrical discharge that occurs during thunderstorms. It is typically the result of the buildup and release of electrical energy within the atmosphere. When different charges accumulate, a powerful electrical discharge seeks to equalize the charge separation, resulting in lightning.

2.2 The Science Behind Lightning Strikes

Lightning strikes can occur between clouds, within a cloud, or between a cloud and the ground. When a sailboat is present, it can act as a conductor, attracting lightning due to its height and metallic components. The mast, rigging, and other metallic elements increase the likelihood of a sailboat being struck by lightning.

2.3 Factors Affecting Lightning Strikes

Several factors influence the frequency of lightning strikes on sailboats. These include geographical location, prevailing weather patterns, topography, and the height of nearby objects. Sailboats in areas with a higher frequency of thunderstorms and lightning activity are naturally at a greater risk.

3. Lightning Safety Measures for Sailboats

To minimize the risks associated with lightning strikes, sailboat owners should consider implementing various safety measures.

3.1 Importance of Lightning Protection Systems

Installing a lightning protection system on a sailboat is crucial. These systems consist of grounding, bonding, and surge protection devices that help dissipate the electrical charge and direct it safely into the water.

3.2 Grounding and Bonding

Proper grounding and bonding techniques ensure that the electrical charge is efficiently discharged into the water rather than passing through the boat’s interior. Grounding plates and conductive materials are strategically placed to provide a low-resistance path for the electrical discharge.

3.3 Surge Protection Devices

Surge protection devices are essential components of a lightning protection system. They are designed to divert excess electrical energy and prevent damage to sensitive electronic equipment on board.

3.4 Lightning Rods and Dissipation Systems

Lightning rods or dissipation systems can be installed on sailboats to attract lightning strikes and safely direct the electrical energy away from the boat’s vital components.

3.5 Best Practices for Sailors

Sailors can take additional precautions to minimize the risk of lightning strikes. These include monitoring weather forecasts, avoiding sailing during thunderstorms, seeking shelter in a safe harbor, and disconnecting sensitive electronic equipment during storms.

4. Frequency of Lightning Strikes on Sailboats

Determining the exact frequency of lightning strikes on sailboats is challenging, as it depends on various factors. However, according to anecdotal evidence and insurance claims, it is estimated that around 1 in 1,000 sailboats gets struck by lightning each year.

5. Real-Life Incidents of Lightning Strikes

Numerous documented incidents highlight the risks of lightning strikes on sailboats. These incidents range from minor electrical system damage to severe structural damage or even sinking. Sailboat owners should be aware of these real-life scenarios to understand the potential consequences and take appropriate safety measures.

6. Insurance Considerations for Sailboat Owners

Due to the risks associated with lightning strikes, sailboat owners are advised to obtain appropriate insurance coverage. Insurance policies often cover damages resulting from lightning strikes, providing financial protection in case of accidents or disasters.

7. Conclusion

While sailboats can be vulnerable to lightning strikes, understanding the risks and implementing appropriate safety measures can significantly reduce the likelihood and potential damage. Sailboat owners should prioritize the installation of lightning protection systems and follow best practices to safeguard their vessel and crew. By staying informed and taking necessary precautions, sailboat enthusiasts can continue to enjoy their maritime adventures with confidence.

8.1 Can lightning strikes sink a sailboat?

While lightning strikes can cause severe damage to a sailboat, sinking is relatively rare. However, it is crucial to have appropriate safety measures in place to mitigate the risks.

8.2 Are all sailboats at equal risk of lightning strikes?

Sailboats with taller masts and more metallic components are generally at a higher risk of lightning strikes. However, any sailboat can be affected, regardless of its size or construction.

8.3 Can lightning strikes cause fires on sailboats?

Yes, lightning strikes can cause fires on sailboats, especially if they ignite flammable materials or damage electrical systems. Implementing proper safety measures and fire prevention techniques is essential.

8.4 How can I protect my sailboat from lightning strikes?

To protect your sailboat from lightning strikes, consider installing a lightning protection system, including grounding and bonding techniques, surge protection devices, and lightning rods or dissipation systems.

8.5 Should I avoid sailing in stormy weather?

It is highly recommended to avoid sailing during thunderstorms or stormy weather conditions. Monitoring weather forecasts and seeking shelter in a safe harbor is crucial for your safety and the protection of your sailboat.

Mark Alexander Thompson

Mark Alexander Thompson is a seasoned sailor with over five years of experience in the boating and yachting industry. He is passionate about sailing and shares his knowledge and expertise through his articles on the sailing blog sailingbetter.com. In his free time, Mark enjoys exploring new waters and testing the limits of his sailing skills. With his in-depth understanding of the sport and commitment to improving the sailing experience for others, Mark is a valuable contributor to the sailing community.

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Handling Lightning Strikes on Boats

Lightning strikes on boats can be a nightmare. With a sudden flash and a loud boom, these powerful bolts of electricity can cause devastating damage to boats and, worse, put lives at risk. As a boater, it’s crucial to be well-prepared for the possibility of a lightning strike and understand how to handle such a situation.

In this guide, we’ll discuss the what, which, and why of lightning, how to prepare your boat, and what to do if caught in a storm.

Key Takeaways

• Understand the factors that make some boats more susceptible to lightning strikes, including height, surroundings and construction materials.
• Be aware of the potential consequences of a lightning strike, such as damage to electronics, structural damage, fires, injury to crew members, and damage to onboard systems.
• Recognize the situations and locations where boats are most at risk from lightning, including open water, near tall structures, in anchorages, and in isolated bays or coves.
• Always monitor weather conditions, plan accordingly, and implement a robust lightning protection system to minimize the risk of lightning strikes and ensure the safety of the vessel and crew.
• Knowing what to do if your boat is struck: In the event of a lightning strike, prioritize the safety of your crew, assess and address any immediate dangers, and seek professional help for repairs as needed.

Viral Video UK: Lightning strike nearly hits boat!

The dangers of a thunderstorm.

Lightning is an awe-inspiring yet dangerous natural phenomenon that occurs when electrical charges build within storm clouds and release as a massive discharge. The intense energy from lightning can heat the surrounding air to around 30,000 Kelvin, causing a rapid expansion of air and creating the thunder we hear.

Boats, especially those with tall masts or antennae, are particularly vulnerable to direct lightning strikes due to their height and isolation on the open water. When a boat is struck, the electrical energy can cause extensive damage to the vessel, including:

• Frying electronics and electrical systems
• Igniting flammable materials, potentially causing fires
• Damaging rigging, masts, and sails
• Creating holes or leaks in the hull

In addition to the potential harm to the boat, lightning strikes pose a significant risk to the people on board. Injuries can range from mild to severe, including burns, temporary or permanent hearing, vision loss, and even fatalities in extreme cases.

Preventing Damage to Your Boat

A well-prepared yacht or boat is less likely to suffer severe damage from a lightning strike. By installing a lightning protection system, ensuring proper grounding, and taking the necessary precautions during a storm, you can minimize the risk of losing expensive equipment or dealing with costly repairs.

Ensuring Crew Safety

The safety of your crew should always be the top priority. Knowing about lightning behavior and taking appropriate measures to protect everyone on board can be the difference between a close call and a tragedy. Proper preparation helps you avoid panic and respond effectively in case of a lightning strike.

Understanding the Science of Thunder and Lightning

To effectively prepare for and handle lightning strikes on boats, it’s essential to have a basic understanding of how lightning forms, why boats are vulnerable, and how lightning behaves around water. This knowledge will empower you to make informed decisions and take appropriate measures to protect your boat and crew.

How Lightning Forms and Strikes

Lightning forms when electrical charges build up within storm clouds due to the movement of ice particles, water droplets, and air. The separation of positive and negative charges within the cloud creates an electric field, and when the voltage difference becomes too great, a lightning strike occurs.

Lightning typically follows the path of least resistance, which means it seeks out the area’s tallest, most conductive objects. This is why tall structures, like skyscrapers or trees, are often hit by lightning.

Why Boats are Vulnerable to Lightning Strikes

Boats are particularly susceptible to lightning strikes for a few reasons:

• Height: Sailboats, especially those with tall masts, stand out in the open water, making them attractive targets for lightning.
• Conductivity: Boats are often made of conductive materials, like metal or carbon fiber, which can facilitate the passage of electrical currents.
• Isolation: Out on the open water, boats may be one of the few objects that can provide a path for lightning to reach the surface, increasing the likelihood of being struck.

Lightning Behavior Around Water

When lightning does strike water, the electrical current spreads across the surface, following the path of least resistance. This means that the highest voltage is typically found closest to the point of impact, decreasing as it moves away from the strike location.

While saltwater is a better conductor than freshwater, both can still carry electrical currents, posing a risk to nearby swimmers or boats. Additionally, water provides a relatively low resistance path for lightning, which can lead to side flashes – when lightning jumps from the water to a nearby object, like a boat.

Preventative Measures to Avoid Lightning on a Boat

Taking preventive measures and being well-prepared are critical to reducing the risk of lightning strikes and minimizing potential damage.

Proper Boat Design and Materials

• Lightning Protection Systems: Installing a lightning protection system on your boat can help direct lightning safely to the water, minimizing damage. Key components include air terminals (lightning rods), conductive cables, and grounding systems.
• Conductive Materials and Grounding: Ensure your boat’s materials and grounding system are appropriately designed to handle electrical currents. This may include bonding all metal components, installing grounding plates, and using appropriate wiring and connections.

Preparing the Boat for a Storm

• Disconnecting and Storing Electronics: Before a storm , disconnect and store all electronic devices, such as GPS units, radios, and smartphones. This can help prevent damage from power surges caused by a nearby lightning strike. You can place the disconnected electronics inside if you have an oven on board. The oven can act as a makeshift Faraday cage, providing additional protection against electromagnetic radiation.
• Stowing Away Metal Objects: Secure and stow metal objects, like tools or fishing gear, to reduce the chance of attracting lightning or causing injury due to arcing or side flashes.

Monitoring Weather Conditions and Forecasts

Regularly check weather forecasts and watch the sky for signs of approaching storms. Stay alert for sudden changes in wind direction, darkening clouds, or distant rumbles of thunder. Having a reliable weather app or radio on board can be a valuable tool for staying informed.

What to Do During a Lightning Storm on a Boat

When faced with a lightning storm, keeping your composure and taking appropriate steps to protect yourself and any other crew members is essential.

Finding Safe Harbor

Head to the nearest safe harbor or sheltered area like a marina, cove, or protected bay if possible. Additionally, anchoring near tall structures or trees should be avoided as they may attract lightning and pose a hazard.

Reducing Your Chances of Being Struck

• Avoiding Tall Objects and Open Water: If you can’t reach a safe harbor, avoid tall objects, like buoys or other boats, and avoid large, open bodies of water. Lightning is more likely to strike the tallest object in an area.
• Staying Low and Away from Metal Objects: Keep a low profile on the boat and avoid touching metal objects, like the mast, railings, or wheel, as they can conduct electricity. Use non-conductive materials, like wood or plastic, when possible.

Personal Safety Precautions

• Wearing Rubber-Soled Shoes: Rubber-soled shoes can help insulate you from electrical currents, reducing the risk of injury.
• Staying Inside the Cabin If Possible: If your boat has a cabin, seek shelter during a storm. While not completely safe, it does provide an additional layer of protection.

What to do if Your Boat Gets Struck by Lightning

In the unfortunate event that your boat is struck by lightning, it’s crucial to stay calm and prioritize the safety of everyone on board. Here’s what to do if your boat gets hit:

First Aid and Emergency Response

• Assessing Injuries and Administering First Aid: Check for injuries among your crew and administer first aid as needed. Be prepared to treat burns, perform CPR, or address other potential injuries from a lightning strike.
• Calling for Help and Alerting Authorities: Use your VHF radio or a satellite phone to call for help and inform the local authorities or coast guard of your situation. Provide your location, the extent of injuries, and any damage to your boat.

Assessing Damage to Your Boat

• Checking for Fires or Leaks: Inspect your boat for any signs of fire or leaks from the lightning strike. Address these issues immediately to prevent further damage or danger.
• Inspecting Electrical Systems and Electronics: Carefully examine your boat’s electrical systems, wiring, and electronics for damage. Be aware that some issues may not be immediately apparent and require further professional inspection.

Repair and Maintenance After a Strike

When identifying the necessary repairs after a lightning strike, you should list any damaged electronics, rigging, or structural components caused by the incident.

If it is more extensive than expected, you should consider hiring professional assistance to assess and repair your boat , as electrical and structural damage can be complex and require expertise to address correctly.

How Common Are Lightning Strikes on Boats?

Lightning strikes on boats may not be every day, but they happen frequently enough to cause concern in certain parts of the world.

Frequency of Lightning Strikes on Boats

Although it’s difficult to provide exact numbers, BoatUS estimates that the odds of a boat being struck by lightning in a given year are around 1 in 1,000.

Comparing Risks: Boats vs. Other Structures

When comparing the chances of a boat being struck by lightning to other structures, it is essential to consider why boats are more susceptible.

Boats frequently find themselves on open stretches of water, and therefore, they may be one of the tallest objects for miles around, making them an easier target for lightning.

On the other hand, buildings on land are often surrounded by tall objects and other structures that can protect them from being hit.

Why Are Some Boats More Likely to Be Struck by Lightning?

Several factors can make certain boats more susceptible to lightning strikes than others. Here are some key reasons:

Height and Surroundings

Boats with taller masts, such as sailboats, are at a greater risk of lightning strikes as the lightning tends to take the path of least resistance and usually strikes the highest object in the vicinity.

Additionally, boats that are either the tallest objects on the water or near tall structures are more likely to be hit by lightning, particularly in open water where tall structures may be scarce.

Boat Construction and Materials

• Conductive Materials: Boats with conductive materials like metal hulls may be more likely to attract lightning. However, they can also dissipate the electrical charge more efficiently, potentially reducing the damage caused by a strike.
• Non-Conductive Materials: Boats made with non-conductive materials, like fiberglass, may not attract lightning as readily, but they can experience more significant damage if a strike does occur. This is because the electrical current from the lightning may find alternative paths through the boat, damaging electronics and other components.

Lightning Protection Systems

• Presence of a Protection System: Boats equipped with a well-designed and properly maintained lightning protection system are less likely to be struck by lightning or suffer severe damage if a strike occurs.
• Absence of a Protection System: Boats without a lightning protection system are at a higher risk of being struck and experiencing more severe damage.

What Can a Lightning Strike Do to a Boat?

A lightning strike can have a wide range of consequences for a boat, from minor to severe. Damage to electronics and electrical systems is one of the most common outcomes.

The intense electrical current can damage sensitive components, losing essential equipment like navigation systems, communications devices, and other instruments.

Furthermore, structural damage can be incurred if the boat is made of non-conductive materials like fiberglass. The lightning’s current may create holes or cracks in the hull, damage rigging or masts, and compromise the craft’s integrity.

In addition to these two potential outcomes, fires and explosions are possible due to the immense heat generated by a lightning strike. Flammable materials such as fuel tanks or gas lines may ignite easily when exposed to this heat.

Onboard systems may also suffer from damage such as engine failure, fuel leakage, plumbing issues, or impaired air conditioning functionality.

Finally, though rare, crew members may be injured or even killed due to a direct strike or being close to where the lightning has landed.

Long-Term Strategies and Lightning Protection Systems

Regularly inspect and maintain your lightning protection system.

• Routine Inspections: Periodically inspect your lightning protection system, including air terminals, conductive cables, and grounding systems, to ensure they remain in good working condition.
• Maintenance and Repairs: Address any issues or damage to your lightning protection system immediately. This may involve cleaning connections, tightening bolts, or replacing damaged components.

Invest in Quality Equipment and Materials

• Selecting the Right Components: Invest in high-quality components for your lightning protection system, such as air terminals, cables, and grounding plates, to ensure their effectiveness and durability.
• Using Proper Materials: Opt for non-conductive materials, like wood or plastic, for parts of your boat that don’t require electrical conductivity. This can help reduce the risk of side lightning flashes.

Final Thoughts

Lightning strikes can pose a significant risk to boaters. Still, with proper understanding, preparation, and preventive measures, you can minimize these dangers and ensure the safety of your crew and vessel.

By staying informed about the science of lightning, investing in a reliable lightning protection system, and following good boating safety practices, you can confidently navigate stormy weather a nd protect your boat from potential damage.

Remember, the key to handling lightning strikes on boats is a combination of long-term strategies and immediate actions during a storm. Always stay vigilant, educate yourself and your crew, and keep your boat well-maintained to reduce the risks associated with lightning.

Q: Can my boat’s lightning protection system guarantee it won’t be struck by lightning?

A: No, a lightning protection system cannot provide a 100% guarantee that your boat will not be struck by lightning. However, a well-designed and maintained system can help minimize potential damage and ensure the safety of your crew in case of a strike.

Q: Are powerboats or sailboats more likely to be struck by lightning?

A: Sailboats, especially those with tall masts, are generally more likely to be struck by lightning due to their height. However, powerboats are also at risk and should take precautions to protect their crew and equipment.

Q: How often should I inspect my boat’s lightning protection system?

A: Inspecting your lightning protection system at least once yearly (or more frequently if your boat is often exposed to severe weather) is recommended. Additionally, you should always thoroughly inspect after a lightning strike or if you notice any signs of damage or wear.

Q: Are some boats more susceptible to lightning strikes?

A: Height, surroundings, and construction materials can make some boats vulnerable to strikes.

Q: What can a lightning strike do to a boat?

A: Lightning strikes can cause damage to electronics and electrical systems, structural damage, fires or explosions, and injury to the crew.

Cunningham Sailing Techniques for All Wind Conditions

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How Often Do Sailboats Get Struck By Lightning?

Last Updated by

Daniel Wade

April 26, 2023

‍ Key Takeaways

• A lightning protection system can help mitigate a lightning strike.
• Lightning storms can form anytime when offshore sailing so prepare the best you can.
• If you see lightning strikes nearby you should move to the middle of the boat.
• Multihull sailboats attract lightning more than other types of boats.
• Perfect lightning protection does not exist so plan accordingly before sailing.

‍ Sailing during rough weather can be a dangerous situation. But how often do sailboats get struck by lightning?

Sailboats are hit with lightning strikes at a rate of four per 1,000 on average. Various boats in Florida on average have a rate of 3.3 out of 1,000, so location matters. The chance of any boat being struck by lightning in a given year is one in 1,000.

According to insurance claims for places like Florida that get hit with lightning strikes often every year, these numbers only reflect reported damage to sailboats. Marine surveyors warn that these numbers could be slightly higher so the chance of your boat being struck by lightning is still dangerous no matter how little or significant the risk is.

Table of contents

‍ The Chances of Sailboats Being Hit by a Lightning Strike

Some will argue that the size and type of your boat do not matter when it comes to lightning strikes. This is not true since some boats have been reported to be more susceptible to lightning strikes than others.

Lighting strikes are not your fault but there are some things you can do to help lower the chances of your sailboat being struck by lightning. While there is no guarantee in a lightning protection plan, having all materials and actions ready beforehand could save you money and someone’s life.

Multihull Sailboats

Multihull sailboats like catamarans or trimarans have a 6.9% chance of lightning strikes a year out of 1,000. Multihulls lack keels and with more exposed surface area face a greater risk of lightning strikes. Modern multihulls come with complex electronic systems that usually lead to costly damages from a lightning strike.

Monohull Sailboats

Monohull sailboats have a slightly lower occurrence of lightning strikes than multihull sailboats at 3.8% out of 1,000 per year. Just because they are less likely to be hit with lightning than multihulls does not mean you are in the clear.

Other Types of Boats

Other boats such as trawlers, bass boats, and even pontoon boats are at lower risk individually. These boats have less surface area and some are not even designed to be offshore where storms are intense. When combining those and all other boats besides sailboats, the risk of being struck by lightning is 0.9 out of 1,000.

Length of Sailboat

Your mast is an extension of your boat so you should sit and wait for the weather to pass before heading out to sea. According to Martin Uman, who leads the Lightning Research Group at the University of Florida , sailboats with 20 to 30 feet taller masts are almost three times more likely to be struck by lightning. This is due to the nature of electrical charge transfer between clouds and the ground despite lightning bolts being typically five miles long and one inch wide.

Sailing in the Rain

Rain clouds hold water and thunderstorm clouds carry electric charges. Interestingly enough, sailing in the rain is fine, but the accumulation of storm clouds is dangerous. Your focus should be on Nimbostratus and Cumulonimbus.

Nimbostratus clouds are flat, large, and closer to the ground. They can produce precipitation and span vast areas at a time. Safe boating in these conditions requires proper measures such as adequate rain protection, safety gear, GPS, and lighting for navigation and anchoring.

Why Are Sailboats a Target for Lightning Strikes?

Lightning strikes can hit boats during a lightning storm since some have metal masts and antennas. You are more susceptible to a lightning strike due to conductive material and turning your boat into a giant lightning rod.

This is especially true for sailboats with high aluminum masts since lightning can hit the mast before anywhere else on the boat. Fiberglass boats sitting low on the water are less likely to be struck by lightning.

How to Prepare for a Potential Lightning Strike

Boaters must be familiar with essential safety guidelines for thunderstorms. A practical approach to lightning protection is providing a safe discharge path for lightning. No technology currently exists to prevent lightning strikes so preparing for the worst is all you can do.

Update Insurance or Check the Policy

Ensure your sailboat has adequate insurance. If you do not have any or want to change you could always check out what BoatUS Marine insurance can do for you.

Seek Weather Updates

Equip modern weather detection gear and check the forecast before sailing. If thunderstorms are predicted you should stay in the harbor until the weather clears.

You can always tune into the VHF radio weather channel that is typically found on channels one through nine depending on your area. This gives you timely storm updates and critical information if you are out while a storm arrives.

If Stuck in the Middle of a Storm

Storms that will likely produce lightning strikes can pop up at a moment's notice at sea. If you are unable to outrun the storm, here are a few tips to consider:

• Wait it out and keep your shoes on while avoiding metal objects.
• Hold onto non-conductive items like fiberglass but beware that water can conduct electricity.
• Keep a hand in your pocket for safety and ensure no metal is inside.
• Use a vital piece of wood or rubber to control the steering wheel and set the throttles at idle or low throttle.
• Lower the antenna, outriggers, and any fishing rods.
• Stay close to the middle of the boat and remove any metal jewelry.
• If lightning strikes the boat you should immediately ask if everyone is okay and look for a hole that the lightning went through to ensure you are not taking on water.

Keeping Electronics Safe

It would be best to use transient voltage surge suppressors (TVSS) to safeguard crucial and lightning-sensitive equipment such as ECU/ECM, chart plotters, and instruments. These semiconductor devices suppress lightning-induced voltage spikes and are widely used in aviation, wind power, and telecommunications.

TVSSs function like voltage-sensitive fuses and redirect excess voltage as heat. Using TVSSs is a wise investment in preventing lightning damage to equipment even though this heat may damage them.

Ground Your Sailboat

For a grounding system, you should install lightning rods or terminals on top of the mast and connect them to the grounding plate to protect it from lightning. Use cable as a down conductor for wood or carbon masts and retrofit the grounding plate during haul out.

Monohulls require one plate, while ketches, yawls, and schooners need a path for each mast and a strip under the hull. Catamarans need two plates but a more extended plate outline is better for current dissipation.

Internal Bonding Circuit

A bonding system is a circuit inside a boat that links main metal objects to the grounding plate with cables. This reduces the risk of internal side strikes caused by current jumping between objects towards the ground.

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I've personally had thousands of questions about sailing and sailboats over the years. As I learn and experience sailing, and the community, I share the answers that work and make sense to me, here on Life of Sailing.

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Lightning Protection

• Thread starter captcoho
• Start date Apr 9, 2022
• Forums for All Owners
• Ask All Sailors

After reading older and not so old threads, how many sailors favor grounding their mast and rigging ?  

Captain Larry-DH

I grounded my mast and rigging on my last boat. It was struck twice in 11 years. No hull damage, but a few rigging fittings showed scorch marks and were replaced as a precaution. Extensive electrical damage throughout the boat, both times. Melted VHF antenna both times. Does it attract lightning if you ground? Maybe. I can’t find anything conclusive on that question. I’ve heard of ungrounded boats that were struck too. I think a clear path to ground helps limit extent of damage if you’re struck, so I favor it for that reason. My new boat will be more challenging to ground, due to wire runs (catamaran) but I’ve already installed the Dynaplates. Connection on port side doesn’t have a path that can be totally hidden in unfinished areas, so I’m still thinking that one through. PS - Dynaplates do not explode from a direct strike. I’ve proven that by experience, twice. (I’ve read it on the web based on the theory that the porous metal can explode from internal steam pressure build up. Hogwash.)  

I don't. The fact that lightning is so powerful and unpredictable that it is deemed to strike where it may defies any attempts to control it. There are unproven theories about factors that may prevent or attract lightning strikes and increase or diminish the damage but the data does not support any. I have opted to observe the data regarding lightning strikes on boats and use this data to try to try and minimize the occurrence of a strike. A good and well stablished statistical fact is that the occurrence of loss of life due to a lightning strike on a sailboat is nearly nil year after year. (the same cannot be said for Golf Courses) That alone has removed any fear from sailing near lightning. Another statistical fact is that the majority of lightning strikes occur near land as opposed to open waters. I only really care about the boat getting hit by lightning if I am aboard; as when it is docked and unattended it will be protected by insurance. When sailing I will steer the boat away from land. It is also prudent to get away from a lee shore in the accompanying storm conditions. There are a few theories about "cone of protection", grounding the mast, installing diffusers but they are all at best unproven. Seems to me that the cone of protection and grounding of the mast are mutually exclusive as grounding may seem to attract lightning instead of repelling it. Both theories remain unproven so it would be a personal matter of choice as to which to follow by faith. Very fortunately, remember the odds against getting hurt are very favorably on our side.  

I do. My thinking is that a lightning strike is going to find the most direct way through the boat to the water. Either through a planned ground connection or possibly right through the hull, which could sink the boat. Either way, the electrical system and electronics would be fried, and fire is still a possibility from that, but providing a direct path to the water seems logical to me to minimize damage. As an architect, every tall building I designed was grounded with lightning rods, a proven invention we owe to Benjamin Franklin. An aluminum mast is effectively a lightning rod and the upper portion of Franklin’s system. It needs to be grounded as directly as possible to the water.  

We are fabricating a new 1/8" x 1.5" stainless steel grounding connector now to attach to one of our keelbolts.  

PaulK said: We are fabricating a new 1/8" x 1.5" stainless steel grounding connector now to attach to one of our keelbolts. Click to expand

Dalliance said: Mine may be a similar, less robust, approach. I have a copper ground wire from the aluminum mast base, down the compression post, to a stainless steel keel bolt almost directly below. External lead keel. Liberal application of Lanocote at the dissimilar metal connections. Click to expand

SBO Weather and Forecasting Forum Jim & John

captcoho said: how many sailors favor grounding their mast and rigging ? Click to expand

I favor having the rigging grounded. A number of years ago a physicist friend of mine said a grounded boat is more likely to get hit, but less likely to suffer catastrophic damage. I don't know how reliable that info is, but I still go by it. My understanding is that lightning does not seek out a target. When it is ready to discharge it does so immediately through the least resistant path. So if that discharge moment occurs a hundred feet from your boat, chances are your 60 foot mast is not the most direct path. Additionally, the rigging provides the crew protection as, I think, it forms a Faraday cage. This is often referred to as the "cone of protection" referred to in Power Squadron materials. If you cruise or distance race you are going to get caught out in lightning at some point.  

Dalliance said: I do. My thinking is that a lightning strike is going to find the most direct way through the boat to the water. Either through a planned ground connection or possibly right through the hull, which could sink the boat. Either way, the electrical system and electronics would be fried, and fire is still a possibility from that, but providing a direct path to the water seems logical to me to minimize damage. As an architect, every tall building I designed was grounded with lightning rods, a proven invention we owe to Benjamin Franklin. An aluminum mast is effectively a lightning rod and the upper portion of Franklin’s system. It needs to be grounded as directly as possible to the water. [/QUO Click to expand

RoyS said: I have grounded my mast to my lead fin keel. Once while sailing a lightning bolt struck the water about a hundred feet from my boat. This led me to believe that my grounded mast did not attract lightning or that lightning bolt would have chosen my grounded mast instead of the water surface 100 feet away. Click to expand

To further add to the confusion, the oft repeated statement that electricity takes the path of least resistance is simply not true. Electricity takes all available paths. Proof of the latter statement is in any parallel circuit.  

There is no confusion on the SCIENCE involved on Lightning Avoidance [Protection is implies a Shield] You use SCIENCE to minimize your chances of being lightning's path to a Ground. This is True on Land or Water [Marina, On the Hard, or Open Sea for boats]. My best comparison of Land and Sailboats... "Water Towers and Sailboat Masts". The Science works for both examples. Be well Grounded. _____ This link has best info on Lightning and humor too. newbie lightning protection? But I will copy part of my post#5 here. _____ You never need a consensus on a SCIENCE ! However several types of sciences involved, thus the confusion. List in order of your ability to control them... 1) Electrical (flow of electrons) 2) Math (statistics) 3) Religion If you combine all 3 you can reduce your chances of being a target. In a nutshell... 1) Ground your boat and Isolate yourself 2) Buy Insurance 3) Pray it doesn't hit you ________ I will repost 2 pages from this book by Nigel Calder. Boatowner's Mechanical and Electrical Manual: How to Maintain, Repair, and Improve Your Boat's Essential Systems: Calder, Nigel: 9780071432382: Books - Amazon.ca Good Avoidance for your Boats... Jim...  

Attachments

• NIgel Calder Lightning-2.pdf 2.1 MB Views: 70

Found out some interesting things when working at a weapons disposal facility doing safety assessments, Lightening doesn't like to make "tight turns" and is highly unpredictable in the paths it takes, even with proper grounding. There is an NFP standard on lightning protection that is specific to buildings but has applications for us. First, although not stated explicity, the jist is that lightning takes the path it wants to take. For instance, with grounding straps and and these are big flat woven copper, not just small wires (and 10 gauge is small in terms of lightening) are run from the lightning rod to the ground along metal beams, the attachment point must be grounded to the beam. That is because even the robust straps cannot carry the current easliy and it will arch to the beam if not grounded. There is a specification for how sharp the bend can be in the ground strap since if you try to "turn" the lightning around too sharp a bend it will simply go off course and arc to the nest best available path. Think of a race car out of control around a 90 degree turn. Of course this is in common language rather than the techincal jargon of the standard. They also discuss in detail the concept of a "cone of protection" that effective lightning protection can provide. Take aways - I will ground my mast to the keel bolt of my lead keel to do what I can and trust in @JamesG161 solution list: BUT 1. I really doubt the little 10 gauge wire would conduct a lot of the current with a direct hit to the mast but it may do enough good to keep from blowing a hole in the boat. 2. The wire is insulated, but probably only good to about 600V and may very well arc right through that along the way. 3. There are probably several near sharp bends in that wire in its path from the mast to the keel bolt. 4. Insulate yourself as best you can, don't be hanging on the shrouds, backstay or hugging the mast during a lightning storm. Take advantage what cone of protection you do have. With any reasonable mast height the cone covers the whole boat. Probably why more lighning injuries on power boats - no cone of protection. 5. Make sure you are insured. Replacing electronics, a near certainty with a lightning strike may be expensive depending on your boat's equipment 6. Have a good relationship with your "Maker" - never hurts to be in good graces there. I had a lightning strike on my boat, BUT I wasn't even in the water. I was sitting in a travel lift awaiting launch the next morning and not "well grounded" to the water or the ground as far as I can determine. There were the nylon slings holding the boat, the huge rubber tires of the travel lift and the keel was resting on wooden blocks (not very good conductance). Go figure. My mast was about 75-80 feet in the air in the lift but there were other trees taller around. Don't know what that tells you about the advantages of being grounded to the water or not but it is what it is.  

smokey73 said: 1. I really doubt the little 10 gauge wire would conduct a lot of the current with a direct hit to the mast but it may do enough good to keep from blowing a hole in the boat . Click to expand

@JamesG161 Excellent point and something I didn't consider. As you stated, its not so much about "protection" as it is about "avoidance" in making sure the mast is at the same potential as the water. Also make sense now about the strike in the slings.  

smokey73 said: Also make sense now about the strike in the slings. Click to expand

I think I actually had what is sometimes called a "side strike". It hit somewhere else nearby and some portion "jumped" to my boat at the mast and it exited through the keel and the wet wooden blocks to the ground. The VHF antenna was "gone", the connection charred, the stuff at the top of the mast was laying in the cockpit, and all my electronics were damaged but there was no evident "exit wound" and no indication that wiring was damaged. Progessive was my insurance company and the were great! They required the mast be stepped and inspected to confirm it was a lightning strike and make sure everything was repaired. When they saw the black burn marks on the VHF antenna it was "lets get this fixed".  

I like the idea of chains from the boat to the ground. Are they connected to ground rods into the ground or just laying on the concrete or gravel?  

I believe ABYC recommends 6 gauge minimum (4 gauge is better) ground wire from mast base to keel bolt and 8 gauge minimum from chainplates, etc. to keel bolt. Of course connection to the keel bolt is only for external mounted keels, not encapsulated.  

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NO-LIGHTNING

Protect your boat from lightning strikes.

Lightning Threat on Boats

Boats are the sharpest and highest objects on water. Depending on the size and structural properties, risk of getting hit by a lightning strike varies, but if you are the only one under thunderstorm cloud at that moment, you are most likely to experience lightning damage on your boat.

During a storm, ground charges(charges on water) accumulate on the boat, climb up to the top of the mast where wind sensors are located. As these ground charges are emitted towards the oppositely charged streamers of cloud; two charged groups meet each other and develop a conductive channel between the cloud and the mast which is called “lightning”.

All current inside cloud flows through this channel and reach to water through the mast and boat body while damaging all sensors on the mast; destroying antennas, radios, and cables; damaging batteries inside and finally breaking down the engine and causing a fire.

While discharging from the bottom, lightning current can damage the body of the boat and leave holes underneath. 

Lightning Rod "Protection"

Masts are mostly made of metals such as aluminum and/or lightweight steel and they are the most conductive and highest structures on the boat. Even if you have a wooden mast, it is a high and sharp object and still conductive due to salty water particles on its surface. Masts are the primary targets of lightning strikes and must be protected against direct and indirect effects of lightning.

Lightning arresters are used to emit more charges on themselves in order to attract lightning before any surrounding object. With the use of a lightning arrester on a boat mast, the arrester collects all lightning strikes with the purpose of transferring lightning current to the grounding system safely.

However, the lightning current must reach the ground through the shortest and fastest way which is still the mast itself. Even though a conductor cable is installed between lightning arrester and grounding system, lightning current prefers to follow larger surfaces instead of a conductor cable and flows through mast surface.

Using a lightning arrester on boats does not a solution and all sensors, all electronics and engine are still damaged by lightning current and even worse; all people on the boat are under serious risk of getting hit by the lightning current.

Lightning must be kept away from boats!

EvoDis   Lightning Prevention System

The point where lightning hits depends on the ground charge accumulation on a body and emission point on the top. Lightning strikes at that particular point of emission and lightning current run down to the ground through the body of the structure.

EvoDis    Lightning Prevention System  dissipates the ground charges on mast through thousands of tiny sharp points and blocks the emission of these charges by keeping the surrounding electric field strength below the threshold level. This process makes the protected boat “invisible” to lightning; prevents any damage on electronics and sensors and save the boat.

EvoDis   Units are installed directly on the mast without a need for a conductor or any upgrades in the existing grounding system of the boat. EvoDis     Units can be applied with vertical elevation rod or at the top of the mast with a flat base. EvoDis   Lightning Prevention System does not require any maintenance after installation and EvoDis    Units  are delivered with 10-year product warranty.

EvoDis   Lightning Prevention System is a lightning protection solution with 100% success in high voltage laboratory tests and in field tests. EvoDis   has  been applied to hundreds of lightning prone towers, masts and poles worldwide and none of these structures have been hit by lightning since the dates of installation.

Best way of lightning protection is to stay away from the lightning.

EvoDis   Lightning Prevention System keeps lightning away.

You are now one step closer to be free of lightning!

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Carbon masts and lightning

Discussion in ' Multihulls ' started by Richard Woods , Apr 10, 2009 .

Richard Woods Woods Designs

Many months ago there was a debate here about the damage caused to carbon masts by lightning. Some people believed that a carbon mast would not be damaged by lightning. Maybe this, taken from a recent Latitude 38 will change their minds There was a horrendous lightning storm, with huge bolts striking all around Coyote. We finally took a direct hit. The bolt came down the carbon fiber mast, blowing a hole in it, and showering the forepeak — where the woman was trying to hide — with sparks from the windlass. The bolt continued up the mizzen to the radar, then down to the engine. I could see it all even thought I had my eyes shut. Finally, after the deafening noise, there was dead silence. Then I heard the comparatively soft sounds of things like lights and antennas falling off the masts and onto the deck. Finally, all the pumps in the engine room started going on and off of their own volition, and the hull sounded like Rice Krispies in milk. Coyote is actually a Freedom 40 monohull, not that that makes any difference Richard Woods of Woods Designs www.sailingcatamarans.com  

ThomD Senior Member

Last summer I was gazing out the window at our lake, and heard a large explosion followed by what looked like a truck load of 2x4s projected down the beach. A lightning bolt had just hit our large ash in the front yard, and framents, large logs some of them, could be found a hundred yards away in the surrounding fields. Our house was lucky, because the segment blown out of the tree had been on the far side, and no damage was sustained by the house. On the other hand, had anyone been within 30 yards of the claymore effect, I think they could have been killed. So I guess ash is out also.  

powerabout Senior Member

There was a boat in Brighton marina in the Uk last year that had a direct hit ( assumed) and the mast turned to powder, the spreaders and rigging ended up on the deck and black power on all the boats down wind.  

How ya gunna feel in a lightening storm in the Boeing dreamliner?  

One of my friends did Mech eng in the uk where they have a vandergraph that can create lightening type sparks and tested carbon masts with a vendor. They found if the mast was completely covered in epoxy and no carbon exposed, the mast usually survived BUT if the spark can get to a fibre it will burn it and move to the next and so on very quickly so you end up with a tube of epoxy and no carbon. This was very plain on a section that was cut through with no crane and japped. They filmed it and you could see the spark jumping around.. Now why cant I get insurance on my carbon mast now that it is over 10 years old???????  

another lightening story I also have an old J24 that had a direct hit when moored (before I bought it)and the lightening exited the hull in about 5 places as in it blew holes you could put your fist through from the front to aft the aft bulkhead. These were all the places the core was wet! It sank fast right in front of the club in the middle of the day with everyone watching  

peter radclyffe Senior Member

alden, herreshoff, fife, archer, trumpy, nicholson, mylne, watson, stephens, abeking, fox, nevin, fay, just a few builders who are designers, & engineers  

Fanie Fanie

Coyote is actually a Freedom 40 monohull, not that that makes any difference Click to expand...

Chris Ostlind Previous Member

Fanie, I do like the business of ascribing a seeing function to lightning. I'm also not in the camp, as you suggest it. If it were a seeing thing from Thor's lofty place, then how in the devil does the lightning regularly see the very tiny compared to a building, well-earthed lightning rods so affixed? Could it be that the charge is simply seeking ground by a random path of least resistance? I've been in several high altitude electrical storms while mountaineering and have seen a strike hit boulders nearby, while the climbing team was groveling with a full array of metal hardware, our hair standing on end and the most lovely smell in the atmosphere. We found out later that the lightning strike was directly on a surveying marker with a long iron rod driven into the mountain top to hold it in place. Just lucky that we weren't any closer, but that juice knew where to go.  

Hi Chris, then how in the devil does the lightning regularly see the very tiny compared to a building, well-earthed lightning rods so affixed? Click to expand...

Hi Fanie, Regretfully, I'm afraid that you have misunderestimated the complex Scandinavian personality of Thor. ;-) ;-) ;-)  

Possibly and probably. He won't ask where to put his next...  

bruceb Senior Member

Lightning in Georgia In the early 1980s, hobie switched the top of their masts (about 8') to carbon/glass composite for safety from overhead power lines. The halyard was changed to rope, so there is no electrical path on the mast. After the change over, boats seemed to be struck by lightning while sitting on the beach or moored to a dock. (I never was aware of one being struck while in use) The composite section usually exploded, with minimal damage below it. Just an observation, but the damage was impressive, and I never saw it happen to a solid metal mast. Bruce  

Stumble Senior Member

I am wondering if this question stems from in interest in what happens if a carbon mast is struck, or if it would be better to have a carbon mast vs an aluminum one. From a practical standpoint I don't think it really matters what material the mast is since you are still going to have all sorts of electrical antenna up the rig providing a nice metal pathway to the rest of the boat. Which is going to result in some sort of significant structual damage (I have seen seacocks blown out, keel bolts melted, engine shafts kicked out of the hull...). So from that perspective I think the real problem you face is exacally how large are the bilge pumps, assuming you still have some way to power them now that a good portion of your electrical system is fried.  

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I think the 'size' of the lighning must have a big effect in the misfortune of a direct hit. A huge bolt may melt even the alu mast, and disintegrate a carbon mast. Even a non conductive mast is at risk ie a fiberglass or wooden mast. Remember there are wiring going to the top of the mast, I doubt the lighting is going to exemp the wiring just because it is thinner than the alu mast It will still take the shortest path it can. I got hit by lighting once in the '80's, through the telephone when the lighting hit the next door building so it was an indirect hit for me. Very unpleasant to say the least. I was out as a candle, dunno for how long. The building next door's alu aerial was melted and all elctronics in it fried.  

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Carbon Fiber & Lightening

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I just finished watching a program about a SuperPuma helicopter which was ferrying workers to a offshore oil rig in the North Sea. They never made it as they were struck by lightening and the tail rotor let go which resulted in a ditching in Force 10 weather. All 16 passengers and 2 pilots were successfully rescued and nobody was hurt. The investigators from the Civil Aviation Authority in Britain had determined that the tail rotor blades that were originally made from fiberglass were now being made from carbon fiber. They quite unexpectantly discovered that carbon fiber is a greater conductor of electricity than fiberglass by as much as 1000 times. In this case, the rotors while operating in a storm cloud generated enough static electricity to cause a lightening strike which was concentrated at the tail rotor and it exploded causing the crash. With the ever increasing use of carbon fiber for masts, I think a warning should go out to those owners of boats with carbon fiber masts to ensure that their rigs are protected against lightening. Particularly for those folks who live in areas that are prone to lightening. I would also like to see some discussion on this from the experts in carbon fiber construction and lightening science. Somebody's life may very depend on the knowledge glean from this. It was definetly an eye opener for me.  

They probably already know. Ron -- Chances are, folks with carbon fiber masts are well aware of the lightening risk. For a couple of years I lurked on the Freedom Yachts email list here on Sailnet and saw a couple of stories about people losing masts due to lightening. Unfortunately, one guy bought a boat with what he was told were cosmetic cracks in his mast -- only to lose the rig later on in fairly benign conditions. Turned out the mast had been struck by lightening at some point but it was very hard to detect. Next, what about aluminum masts and lightening....? Any better than carbon fiber? When I'm out in a storm I always feel like a target with that 47 foot tall hunk of metal sticking into the air. Oh well.  

The real problem with Carbon Fiber masts is that the resin does not conduct electricity well, while the carbon fiber does... so the heat from the resistance often causes the laminate to delaminate. However, since the damage is often internal to the laminate, it doesn't appear to be significantly damaged and then fails catastrophically, with little or no warning.  

Somebody told me once that knowledgeable insurers will not cover lightning strikes to carbon masts. If true, this is really important, since depending upon the boat a replacement spar can run upwards of $20,000 or more.  

Dog -- Thanks. That really describes what happened to that one fellow with the Freedom. It also makes sense from a conductivity viewpoint, and why an aluminum mast likely will come through a strike unscathed. The metal is a solid conductor and will let the electrical charge follow the grounding path to the keel-- hopefully? From what I have read and observed, these strikes are so powerful that the electricity pretty much goes where it wants, follows whatever path it wants, etc.  

Jones2r hit on a good point. IMHO, if you are worried about lightning strikes as a terminater to your sailing experience you might wish to select a different leisure-time activity. Most all of the "evidence" is anecdotal and barely into the theory category. I'd probably ground my mast and sail on worry free. It's not the type of situation, in a severe strike, you are going to walk away from anyway. In my career on ships I was never struck and our masts were substantially higher than any boats. I could be way off on this-lightning strikes happen all the time-but how often do they hit something of value? After twenty years at sea, I just found out I was suppossed to be worried about lightning-oh wow!  

For Lighting protection, you need a lighting Rod For well over one hundred years the lighting rod has been protecting boats and land based structures from lighting. You folks need to read up on lighting protection Paul Marine Engineering Costa Mesa California  

For lightning grounding/bonding on a boat with a carbon fiber mast, you need to run some seriously heavy cable up the mast. On a boat with an aluminum mast, you can often just use the mast.  

And for over a hundred years nobodies been able to figure out if they really work or not! <G> Farmers don't seem to think so as they've stopped putting them on their barns, but YMMV.  

If you ask three experts about lightening, you will get at least 4 different answers. The bottom line is that there is a lot of conflicting evidence about lightening. If you bond your boat, you attract lightening, if you don't do anything, you do not attract it. So the best option is to not do anything and stay "near" a bonded boat. It never occurred to me that a carbon fiber mast is like a spark plug wire. Resin replaces the rubber cover and it is filled with carbon. Adding a huge copper conductor inside the mast to carry the lightning current to ground defeats the purpose of using CF by adding weight high in the boat. Maybe one of the problems is CF with wire rigging. If you have a CF mast and non metal rigging, I would think that the lightening would not be attracted to the rig? That would only leave a problem when you are miles from nowhere which is when it does not matter what you do. Just an opinion. Cheers Dennis  

Lightning protection systems (Lightning rods) are alive and well. Shortly after I built my present home, we suffered two direct hits within a month. We (very quickly) contacted a lightning rod installer and had a UL master label system installed. Since that time (Over 25 years) our buildings have not been struck again, even though we have had near misses as close as about 50 feet away. As for the notion that nobody installs lightning protection anymore, you should look somewhat closer and you will find that the systems are still there, but perhaps don't look the same. Check out your local broadcast tower (Radio, TV, or cell phone) and you will find that lightning protection is built in.  

sailingdog summed it up in a nutshell. Carbon conducts (though poorly compared to aluminum) while resin is an insulator. As a result you have extreme temperature differences that causes severe expansion and contraction at dissimilar rates. Its almost the same thing as distressing a fiberglass laminate. The glass separates away from resin bonds and you hare left with loose threads of glass. If I remember correctly the list goes: When it comes to lightning, wood explodes, carbon splinters, and aluminum conducts to ground. The problem then is the ground... Anyone try out those funky bottle brush things that are supposed to "dissapate" the earth born lead charge to prevent a strike?  

Those funky bottle brush things only work if the boat is properly grounded...otherwise, they're not doing anything. BTW, a grounded/bonded boat is more likely to get hit than an ungrounded boat, but the damage on an ungrounded/unbonded boat is generally more expensive to repair. It's basically a crap shoot... six of one, half-dozen of the other... higher risk of getting hit/lower risk of catastrophic damage... or lower risk of getting hit/higher risk of catastrophic damage.  

This thread has generated a lot of discussion. As we don't get very much lightening here, I would say that there are very few boats in my area that are grounded. Saying that, I carry a long set of heavy gauge booster cables on board. If there is a threat of severe lightening I will clip one end on the bottom of the mast and throw the other end in the water. So far so good. If I am docked, I will dissconnect the electronics which is fairly easy for me to do.  

Ronbye, I am assuming you have a deck stepped mast. In my "I am an electrical engineer but certainly not a lightening expert" opinion, you may be doing exactly the wrong thing. The bolt of energy is trying to find the path of least resistance to ground. You are placing your mast top at ground potential (water) which may attract lightening but if it is a direct hit, the energy from the lightening will not make the 90% turn at the bottom of the mast to head for the water. Instead it may burn the cabin top or end up arcing from mast to keel burning everything in between. It is difficult to fathom the amount of energy contained in a lightening bolt. Just an opinion. Dennis  

Maybe I have it backwards, but it has seemed from long experience with lightning rods at my home (27 years with no lightning strikes) that their function is to drain static charge off into the air and thereby to equalize potential differences that might otherwise attract a hit. From what I have been able to learn, the rods and connections are not intended to attract lightning, although they are sized to do so. It would seem that an important element in obtaining such protection is a low resistance conductor that is continuous from masthead to seawater, just as it is important to have and maintain effective ground rods in the earth around structures that have lightning rods. The principal problem with lightning protection in a vessel is the great difficulty of providing an effective connection to the water. Ground plates are deemed inadequate unless they have tremendous surface area, and external keels are often coated with material that is not helpful. Add to that the fact that the key hull to water interface seems to be at the waterline, and you get the idea that it isn't quite as simple as connecting a bond wire to a keelbolt. Incidentally, it seems that lightning is a greater problem for boats in fresh water. That is probably because it is a less efficient electrolyte than seawater and therefore impedes the free flow of static charges.  

May I suggest the following site to learn about lightning: http://www.strikeshield.com/ And perhaps this one although some of it is dated: http://www.thomson.ece.ufl.edu/lightning/ To pick out the good points made so far: • The angle from the mast to the ground terminal is important. Keep the angle as slight as possible. • Lightning passes from the ground terminal to the water through the edges not the surface of the plate if that's what you are using. The reason fresh water boats suffer more damage is because fresh water is less conductive than salt water and you need more edge area to compensate. Most fresh water boats don't compensate and it's a big difference. • If you don't ground your mast, data shows you only have a slightly less chance of being struck. However, your chances of damage are much higher, not to mention the added risk to you and your crew from branches of the lightning trying to find a ground. An ungrounded or improperly grounded boat will suffer holes at the waterline from the lightning. • You need a large good conductor to your ground terminal. The bulk of the current actually goes around the surface of the conductor. • It's correct that the "brush" dissipaters need a good ground also. However, the effective area they have isn't enough to discharge the static build up experienced during a strike. Not enough data yet to determine if they can bleed off enough charge to stop some or any strikes. Most are installed incorrectly to a ground terminal, so the data is bad. Wayne  

so, if i have a freestanding cf mast, do i run a 2/0 gage battery cable up the mast to the mast crane, or is the standard awg 8 good enough? Hank  

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• About Lightning
• Frequently Asked Questions (FAQs) About Lightning
• Lightning Strike Victim Data

Safety Guidelines: Lightning

• Go inside if you hear thunder or see lightning.
• If someone was struck by lightning, call for help, assess the situation, respond, and resuscitate.
• Learn indoor and outdoor safety tips to protect yourself and your loved ones from lightning.

Even though your home is a safe shelter during a lightning storm, you might still be at risk. About one-third of lightning-strike injuries occur indoors. Here are some tips to keep safe and reduce your risk of being struck by lightning while indoors.

Avoid water.

• Do NOT bathe, shower, wash dishes, or have any other contact with water during a thunderstorm because lightning can travel through a building’s plumbing
• The risk of lightning travelling through plumbing might be less with plastic pipes than with metal pipes. However, it is best to avoid any contact with plumbing and running water during a lightning storm to reduce your risk of being struck.

Don't touch electronic equipment.

Lightning can travel through electrical systems, radio and television reception systems, and any metal wires or bars in concrete walls or flooring.

• Do NOT use anything connected to an electrical outlet, such as computers, laptops, game systems, washers, dryers, or stoves.
• Equip your home with whole-house surge protectors to protect your appliances.

Avoid windows, doors, porches, and concrete.

• Stay away from windows and doors, and stay off porches.
• Do NOT lie on concrete floors or lean on concrete walls during a thunderstorm. Lightning can travel through any metal wires or bars in concrete walls or flooring.

Don't use corded phones.

Corded phones are NOT safe to use during a thunderstorm. Do NOT use them. However, it is safe to use cordless or cellular phones during a storm.

Protect your pets.

Your pets cannot protect themselves from lightning; it is your responsibility to help protect them. Remove any metal collars, leashes, or harnesses and replace with plastic. Even though metal does not attract electricity, it is a good conductor and can make injuries, such as burns, worse if struck.

Although no place outside is safe during a thunderstorm, you can minimize your risk by assessing the lightning threat early and taking appropriate actions. The best defense is to avoid lightning. Here are some outdoor safety tips that can help you avoid being struck.

Be aware. Check the forecast.

Thunderstorms with lightning in the mountains occur most often during the summer months, in the late afternoon or evening.

• Check the weather forecast before participating in outdoor activities.
• If the forecast calls for thunderstorms, postpone your trip or activity, or make sure suitable safe shelter is readily available.

Beach and water activities‎

Pay extra attention to developing storms if you are at the beach or boating., listen to the forecast..

It is crucial to listen to weather information when you are at the beach or boating. Short-term forecasts are quite accurate, but sometimes miss some very localized storms.

Learn how to read the weather.

• Watch for the development of large, well-defined rising cumulus clouds. Cumulus clouds have flat bases and dome or cauliflower shapes. Cumulus clouds can develop into thunderstorms.
• Once the clouds reach 30,000 feet, the thunderstorm is generally developing, and it is time to head for shore. As clouds become darker and more anvil-shaped, the storm is already in progress.

Watch and listen for distant storm activity.

• Watch for distant lightning and listen for distant thunder. You might hear thunder before you see lightning on a bright day.
• If you hear thunder or see lightning, seek shelter away from the water.

When thunder roars, go indoors.

Remember the phrase, "When thunder roars, go indoors."

• Find a safe, enclosed shelter when you hear thunder. Even if you see blue sky, you could still be in danger.
• Don't resume outdoor activities for at least 30 minutes after the storm. The beginning and the end of a storm are the most dangerous times.
• If you hear thunder while you are at the beach, find a safe, enclosed shelter, such as your car. Do NOT seek shelter under beach picnic shelters.

Avoid open spaces, vehicles, or structures.

• Stay away from open spaces such as golf courses, parks, playgrounds, ponds, lakes, swimming pools, and beaches.
• Avoid open vehicles such as convertibles, motorcycles, and golf carts.
• Avoid open structures such as porches, gazebos, baseball dugouts, and sports arenas. These structures won’t protect you from lightning.

Choose a safe shelter‎

Don't leave your pet outdoors..

Do NOT leave your pet outdoors or chained to a tree during a lightning storm. Doghouses are NOT safe shelters; bring your pet inside.

Seek shelter immediately, even if caught out in the open.

If you are caught in an open area, act quickly to find shelter. The most important action is to remove yourself from danger. Crouching or getting low to the ground can reduce your chances of being struck, but it does not remove you from danger.

If you are caught outside with no safe shelter nearby:

• Immediately get off elevated areas such as hills, mountain ridges, or peaks.
• Never lie flat on the ground. Crouch down in a ball-like position with your head tucked and hands over your ears so that you are down low with minimal contact with the ground.
• Never shelter under an isolated tree. If you are in a forest, shelter near lower trees.
• Never use a cliff or rocky overhang for shelter.
• Immediately get out of and away from ponds, lakes, and other bodies of water.
• Stay away from objects that conduct electricity (such as barbed wire fences, power lines, or windmills).

If you are out in the open water and a storm rolls in, return to shore immediately.

• If you are on a boat in open water when a thunderstorm rolls in, return to shore immediately and seek shelter. Once on land, get at least 100 yards away from shore.
• If you are unable to return to shore, boats with cabins offer some protection. When inside the cabin during a lightning storm, stay away from all metal and electrical components, including the radio, unless it is an emergency.
• If caught in a storm in a small boat with no cabin, drop anchor and get as low as possible.

Protect your boat‎

Separate from others..

If you are in a group during a thunderstorm, separate from each other. This will reduce the number of injuries if lightning strikes the ground.

Don't stay near tall structures.

Stay away from tall structures, such as telephone poles and trees; lightning tends to strike the tallest object around.

Don't carry metal.

• Don't carry any metal objects, such as golf clubs, fishing poles, umbrellas, or backpacks with metal frames. Metal doesn't attract electricity, but it is a good conductor. Your chances of a direct hit are higher when you are carrying a conductor above shoulder level.
• Be sure to avoid other metal objects as well, such as wire fences. You are more likely to be burned if you are in contact with metal when you are struck by lightning.

First Aid Recommendations

Giving first aid to a person who has been struck by lightning while waiting for professional medical attention can save their life. It is safe to touch people who have been struck by lightning; they DO NOT carry an electrical charge.

Follow these four steps immediately to help save the life of a person who has been struck by lightning:

Call for help.

• Call 911 immediately—It is safe to use a cell phone or cordless phone during a storm.
• Give directions to your location and information about the person.

Items to Note When Calling for Help‎

Assess the situation..

Safety is a priority. Be aware of the continued lightning danger to both the person who has been struck and the rescuer.

• If located in a high-risk area (for example, near an isolated tree or in an open field), you could be in danger. If necessary, move to a safer location.
• If it's safe to do so, move the victim to reduce the risk of further exposure to lightning. Do not move victims who are bleeding or appear to have broken bones.

It is unusual for a person who has survived a lightning strike to have any major broken bones that would cause paralysis or major bleeding complications, unless the person suffered a fall or was thrown a long distance.

Please Note‎

Lightning often causes a heart attack.

• Check to see if the person is breathing and has a heartbeat.
• The best places to check for a pulse are the carotid artery in the neck and the femoral artery in the groin.

If the person is breathing normally, look for other possible injuries.

Lightning can cause burns, shock, and sometimes blunt trauma.

• Treat each of these injuries with basic first aid until help arrives.
• If the area is cold and wet, putting a protective layer, such as a jacket, blanket, or plastic sheet, between the person and the ground may help decrease hypothermia (abnormally low body temperature).

Resuscitate.

• If the person is not breathing, immediately begin mouth-to-mouth rescue breaths.
• If they do not have a pulse, start chest compressions as well (CPR).
• Continue resuscitation efforts until help arrives.
• Natural Disasters and Severe Weather
• American Red Cross: Thunderstorm Safety
• National Weather Service: Lightning Safety
• Ready.gov: Thunderstorms and Lightning

You can protect yourself and your loved ones if you know what to do when you see lightning or when you hear thunder as a warning.

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• Practical Boat Owner's Reader to Reader

Lightning protection for steel hulled boat

• Thread starter Lomax
• Start date 28 Jan 2017
• 28 Jan 2017

My boat (steel hull & superstructure) has a ~3.5m tall wooden mast (not for carrying sails), which is festooned with various bits of equipment; navigation lights, antennas, weather instruments, etc. It is mounted on the cabin roof, which sits approximately 1.5m above the water, so the top of the mast is about 5m from the wet. I am worried that it could potentially(!) attract lightning, especially with all the electrical conductors running down it. What steps can I take to ensure that if I get hit by lighting 1) those on board remain safe 2) electronic equipment connected to the mast doesn't get damaged? Edit: More specifically, I am wondering if it would be worth putting a "lightning rod" on top of the mast, and connecting this to the cabin roof with a hefty cable. Also whether inline "lightning arrestors" or "surge protectors" on the wires going up the mast provide a good level of protection for the equipment at the other end.  

Well-known member

NormanS said: Stay close to saily boats with tall masts. Click to expand...

If you are concerned about lightning protection then yes A heavy gauge cable from a conductor on the top down to the cabin top should provide protection for the mast. Surge protectors like voltage dependant resistors would be useful on light wiring. However I am not sure that they would permit the radio to work well with them on the antenna cable. An antenna with a coil inside to ground providing a DC short might be preferable but this might evaporate pretty quickly with the induced currents so perhaps you should accept that the VHF radio might be lost in a strike. Disconnect if a storm approaches might be the best idea and carry a HH VHF. In the end much depends on where you sail (some places are a far greater risk of lightning than others) and your own personal concern. Funny today is forecast to have thunder storms here and I am going to do a race this afternoon. Lightning is not so common here. I don't know of any boats being struck although many years back our club radio tower got a hit but with no real damage. I will probably just hope for the best. Although if I was concerned I would connect a heavy cable from ali mast base to a conductor plate or chain in the water. olewill  

• 29 Jan 2017

Active member

There is a debate about whether gas ovens and microwave ovens are Faraday cages. What I would have done if lightning was close is disconnect all electrical kit and put everything in our gas oven and cover the glass with multiple layers of tin foil. Anything at the top of the mast will be destroyed as we saw when we had a boat park next to us on a pontoon in Trinidad that had been hit by lightning. He hadn't tried to make a Faraday cage or at least disconnect all the electrical kit so everything was destroyed. The most interesting thing was there was a scorch mark on his small red ensign on the back stay. We were sailing at night off the Venezuelan coast and the radar showed lightning building all around us, I was on watch and I heard the loudest bang I've ever heard, the brightest flash I've ever seen and the smell of ozone, I hadn't prepared anything because it was cloud to cloud. The closest we came was on passage from Grenada to Mustique an unexpected squall line formed close by, lightning hit the water about 30 yards in front of the boat and we had Elmo's fire crackling in the rigging but no damage.  

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