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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Modern Lightning Protection On Recreational Watercraft

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While you can't prevent a strike, there's a lot you can do to mitigate — or even prevent — damage.

A thunderstorm passing over a marina has the potential to cause expensive damage.

The recent advances in electrical and electronic systems have revolutionized recreational boating. Vessel operations have been simplified and the boating experience enhanced due to the integration of electronics into almost every onboard system, from navigation and communications to propulsion and maneuvering. Complex engine electronics known by various names including Engine Control Unit (ECU) and Engine Control Module (ECM) have increased performance and reduced emissions on modern engines. However, these advances have come at a cost. Many 21st-century boaters depend on electronic systems to navigate and maneuver their boats, and many modern engines will not function if their electronics are compromised. That makes modern mariners and their boats vulnerable to a lightning strike that damages these now mission-critical systems, potentially leaving the boat dead in the water without navigation or communications equipment.

Unfortunately, sensitive electronics on boats have become increasingly vulnerable to lightning strikes, yet lightning-protection systems have not kept pace. It's not that there haven't been significant advances in lightning science since Benjamin Franklin developed his theories on how to protect barns and livestock. The National Fire Protection Association, Underwriters Laboratories, and industries which are significantly at risk from lightning, such as telecommunications, wind generation, aviation, and fuel, have achieved consensus on the science of lightning protection and have embraced new protocols and practices. But the recreational boating industry has been slow to adapt those changes to the marine environment. There are at least three reasons for that.

There is no evidence from independent laboratories that these fuzzy lightning dissipators prevent strikes.

First, corrosion and motion on board boats, as well as limitations with respect to weight, space, and geometry, make lightning protection more challenging than in shoreside installations. Second, the mandate of the standards body for the industry, the American Boat & Yacht Council (ABYC), focuses on protecting life; protecting equipment has been a lower priority. Third, there has been strong disagreement between professionals about the best way to mitigate damage in a lightning strike and precious little data to support one point of view over another. The sometimes-raucous debate surrounding certain unproven lightning- protection devices and such theories as "fuzzy" lightning dissipation terminals and early-streamer emission terminals, as well as unorthodox placement of grounding terminals (a.k.a. grounding plates), have sharply divided the recreational boating technical community, all of which makes consensus on lightning protection difficult, if not impossible.

This lack of guidance is frustrating for those with boats at risk. While a runabout in Portland, Oregon, or a daysailer in Portland, Maine, may have little risk of lightning damage (see " Striking Lightning Facts "), larger vessels (particularly sailboats) in such lightning-prone areas as the Chesapeake Bay or Florida absolutely should be protected using the best technology available. Any marine-insurance adjuster can attest that the potential for loss on these vessels can be great. The National Fire Protection Association made some fundamental changes to the watercraft chapter of NFPA 780: Standard for the Installation of Lightning Protection Systems in 2008 that incorporate the thinking that has become accepted in other industries. While the recommendations in NFPA 780 have yet to be embraced by the recreational boating industry as a whole, understanding what it says — and why — may assist you in developing a lightning-protection plan for your boat.

Lightning 101

The simplest way to think of a lightning strike would be as a short circuit between the cloud and the earth. The earth and an active thundercloud have either a positive or a negative polarity with respect to each other, just like battery connections that can arc if they are not separated by a long enough air gap. Whether the positive charge is in the cloud or on the water may have great importance to a physicist, but matters little to the cow in the barn or the VHF radio antenna on the mast.

The important point is that the earth (or in our case, the water) contains an unlimited supply of positive and negative charges; it is the thundercloud that induces the charge concentration in the water. For example, if a large concentration of negative charge coalesces in a storm cloud over the ocean, a large concentration of positive charge is drawn to the very top surface of the water directly beneath it. (Opposites attract.) Since air is a good insulator, no electricity will flow between the cloud and the water unless the airborne charge loses altitude, moves close enough to the surface of the water, and the lightning jumps the gap. If an electrically conductive material, such as an aluminum tuna tower or mast, stainless steel rigging, or a long vertical copper wire, comes between the cloud and the water, then the gap that must be jumped becomes shorter. The boat short circuits the voltage, much like a wrench across battery terminals.

Because boats are built from electrically conductive components installed between the water and the areas aloft (masts, rigging, antennas, towers, support structures, electrical wiring), a lightning strike is inevitable if an active thundercloud containing electrical charges passes overhead at a low enough altitude. How much damage the lightning strike does to the boat depends upon how easily the electrical energy from the strike can find its way through the boat to ground. There will be a lot less damage if the discharge is contained in a well-designed lightning-protection system than if it takes a detour through the ship's wiring and sensitive electronics on its way out of the boat.

This is a basic concept that surprises many boaters: A lightning-protection system is not designed to prevent a lightning strike, but rather to provide a safe discharge path for the lightning. This is the only viable solution for lightning protection (short of going back to wooden ships, kerosene lamps, and sextants). The technology to prevent lightning strikes does not yet exist.

Still, there are devices out there claiming to do just that. Lightning dissipaters (LDs) look like metal bottle brushes or frayed paint brushes and are installed on the top of the mast. The hypothesis is that the numerous conductive points on the LDs safely dissipate accumulated charges so the lightning strike will not occur. As far as I am aware, not a single independent testing laboratory has confirmed the effectiveness of lightning dissipaters as lightning preventers.

Early-streamer emission (ESE) terminals have also gained traction in some circles. Fancy lightning rods often shaped like a torpedo that usually come with electronic circuitry, these are supposed to attract lightning better than a standard lightning rod (also called an air terminal), to ensure that the lightning strikes the grounding path rather than what is being protected. Once again, I am not aware of any independent studies validating the effectiveness of these devices.

Lightning-protection systems actually function by acting as the "best" short circuit between the cloud and the water, one designed to lead the lightning harmlessly to ground. The system accomplishes this in two ways: by attracting lightning away from more destructive pathways between cloud and ground, and by sending the charge around, instead of through, what it is protecting.

The first concept has traditionally been known as the "cone of protection" or the area protected by an air terminal from a strike. Traditionally, the cone of protection has been thought to include a circle centered on the base of the air terminal whose radius equals the height of the terminal and to extend from the top of the air terminal to the ground at a 45 degree angle. In fact, the length of the final jump that lightning takes before striking the air terminal is about 30 meters. Recent research suggests that the actual area protected can be defined by an imaginary sphere with this radius that is "rolled" up to the air terminal. All objects inside the imaginary sphere will not be protected by the air terminal, which means the area protected often differs in size and shape from the cone of protection model. Modern lightning protection for airports and power plants use the rolling sphere method and place air terminals so that the areas of protection overlap and include any sensitive equipment that would be damaged by a strike.

The second concept will be familiar to many as the Faraday cage. As early as 1836, Michael Faraday discovered that objects surrounded by metal were protected from lightning (explaining why we are safe from lightning while in our cars). Many old-school sailors have used Faraday's discovery to good purpose when they placed sensitive electronics in the oven during a lightning storm (with the oven off, of course.) This practice can be significantly updated by placing sensitive electronics in the microwave oven!

21st Century Lightning Protection

Benjamin Franklin pioneered lightning protection in 1749 with the invention of the lightning rod, and, when it comes to recreational boats, until recently, little has changed. Under his model, the lightning is attracted to the lightning rod (air terminal), which then passes the lightning current harmlessly to a submerged metaevent secondary flashes from these metal structures.

Air Terminals are shown in green; grounding plates with down, side flash, and equalization conductors in yellow; loop conductors in red; and catenary conductors in blue.

NFPA 780 draws much from the old-school system while incorporating improvements based on the modern understanding of lighting protection. While solutions will vary depending on the boat, let's talk about the basics.

Air terminals (lightning rod or Franklin rod) should be installed at the highest points of masts, towers, etc. On a sailboat a single air terminal could be bolted to the mast; on a sportfish it could be bolted to the tower and made to look like an antenna. This should be higher than anything you are trying to protect from a lightning strike, such as a VHF antenna.

A heavy electrical conductor should be connected from each air terminal directly down to a grounding point on the hull. In the case of a sailboat's mast, aluminum is a good conductor, so no separate wiring run needs to be installed. (Note that the wiring inside of the mast will be protected due to the Faraday effect.) An aluminum tower will work the same way on a sportfish so long as the legs are connected to an adequate grounding plate. Where no aluminum structure exists to act as a down conductor, a 4 AWG wire or larger should be run from the air terminal to the grounding plate in as straight a run as possible and well separated from other wiring.

The grounding point should be a corrosion-resistant metal plate installed on the exterior of the hull below the waterline. The plate should be at least one square foot in size and at least 3/16 of an inch thick. Research shows that most of the electrical discharge occurs along the edges, so a long, narrow plate, especially one with grooves cut in it, will be most effective at dispersing the charge. A new major point of contention is where to install the grounding plate, or plates. Some research indicates that a location at or near the waterline is by far the most effective solution. On a sailboat, the lead keel can be used as the grounding plate if the keel is not fiberglass-encapsulated or covered in fairing. If the mast is solidly keel stepped, there would be no need for a separate conductor from the mast to the keel. Metal rudders or propeller struts are also acceptable as grounding plates.

Protecting Electronics

Surge-protective devices (SPD) or transient voltage surge suppressors (TVSS) should be installed on all equipment that's mission critical, expensive, difficult to replace, and/or prone to lightning damage. Examples include the ECU/ECM, alarm systems, chartplotters, and instruments.

A bank of TVSSs protecting sensitive electronics.

TVSSs are the most exciting development in the field of lightning protection. These semiconductor devices provide protection by suppressing lightning-related voltage spikes. They are widely used in the telecommunications, wind generation, and avionics industries.

TVSSs are connected across the input terminals supplying voltage to a piece of equipment; they can be thought of as fuses that react to voltage instead of current. The TVSS is an open circuit as long as the supply voltage feeding the equipment is in the normal range. However, if a lightning strike causes a momentary voltage spike and puts, say 1,000 volts on a 120-volt device, the TVSS will "clamp" or short circuit 880 volts and convert it to heat. The excessive heat could, and probably would, damage the TVSS; but destroying a $250 surge arrestor to protect a $5,000 engine controller is good engineering.

Grounding plates should be long and narrow with groves cut into them to disperse the charge more efficiently.

Voltage surge protection would be prudent for engine controls, navigation systems, steering systems, and shorepower systems. TVSSs come in many voltage ratings, energy ratings, response times, and so on. Some are designed to protect whole distribution systems, while others are suitable for individual equipment protection only. A well-designed system includes cascaded protection, with extra protection on mission-critical and lightning-prone equipment, such as main engines and shorepower systems. The key to a reliable and cost-effective system is to ensure that appropriately rated devices are specified and properly installed. The best TVSS in the world will be ineffective if it is not connected properly.

Despite the best technology, there can still be challenges with an NFPA 780-based system, particularly when the system is improperly or only partially installed. For example, if the air terminal is installed lower than an adjacent antenna, it will not protect the antenna; in that case, the antenna cable carries the lightning current. Also, if the down conductor is connected to the bonding system rather than directly to a dedicated grounding terminal (ground plate), the lightning strike can energize the entire bonding system before discharging into the water. Another common mistake is to secure the lightning down conductor to other wiring. The high current from a strike through the down conductor can result in voltage surges in these adjacent wires, leading to additional damage in equipment that would otherwise be completely unaffected by the lightning strike.

In Conclusion

The recent revolution in marine electronics demands an evolution of our thinking on marine lightning-protection; equipment protection should be an important aspect of any modern lightning protection system. The knowledge and resources to safely transform this change in thinking into reality are readily available, both from the NFPA and industries also at risk from lightning. However, there are unique challenges on pleasure craft that are not addressed by others. These must be solved by sharing the experiences of lightning-protection systems and their effectiveness across the industry.

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James Coté

Contributor, BoatUS Magazine

James Coté is an electrical engineer, ABYC Master Technician, Fire Investigator and Marine Investigator. He operates a marine electric and corrosion control consulting firm located in Florida. For more information, go to: cotemarine.net

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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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• Carbon Fiber Mast, Costs and Benefits
• GMT Carbon Mast, Problems

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.”

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.

Article continues below…

What is a Spanish Plume? Thunderstorms, lightning and downdrafts explained

Earlier this summer we saw considerable thunderstorm activity over the UK and Europe, resulting in flooding and some serious injuries.…

Sailing through calms: Expert advice from ocean racer Pip Hare

Psychologically, I have always found sailing through calms to be far worse than battling any storm. Endlessly flogging sails and…

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!

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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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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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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GETTING ZAPPED! What you should know about lightning and your sailboat By Marlin Bree

"It was one of the few times on Superior I've really been scared." I was aboard my sloop Persistence, bobbing peacefully in beautiful Prince Arthur Marina in Thunder Bay, Ontario, listening to a veteran Canadian sailor. He was sharing a memory with me, the way sailors do, of a sailboat cruise he took on Lake Superior to Isle Royale. "I was out on the open waters," he continued, "and all of a sudden, all around me were lightning flashes, zapping the water. I thought I was going to be next. I was clearly the tallest thing around - and my mast the biggest lightning rod." I could sympathize with him. No question: He was in danger.

Lightning is a serious problem. I recall seeing the results of a lightning strike on a 27-foot sloop in the harbor at Cornucopia, Wisconsin. A few inches above the boat's waterline was a fist-sized hole. The lightning had struck the aluminum mast, followed the mast down into the boat, and, then jumped from the hull into the water. Naturally, all the electronics were fried. No one had been aboard, but if they had, the damage might have been worse than just a hole in the boat and shot electronics.

Basically, lightning is a tremendous electrical charge that occurs in the atmosphere and it is attracted to the tallest nearby object. Sometimes this is a sailboat. The thought of hundreds of thousands of volts running wildly through a lonely boat out on the water is more likely than many boaters realize. In Florida, for example, the Florida Sea Grant estimated that lightning can be expected to hit from four to twenty percent of moored sailboats per year and that cruising sailboats typically get hit at least one time during their lifetimes. Worse, there is no way to protect against a strike. In fact, there is no sure-fire lightning protection. As I built my own 20-foot wooden sloop, Persistence, I contacted lightning experts who told me the only thing that you can do is ease the path of lightning through your boat. You can't stop it from hitting your boat, or shooting through your boat. The best you can hope for is to conduct the lightning strike through your boat in the path of least resistance - one that you have set up. It's called a grounding system. I began by getting a heavy copper plate and through-bolting that to the bottom of Persistence's keelson. This would provide my "ground." Inside the cabin, I secured braided copper wire especially made for a ground to my ground. The wire is about a half-inch in diameter, and, it leads on both sides alongside my wooden mast support to the top of the cabin. Here I fastened the copper wire to the stainless steel bolts holding my stainless steel mast tabernacle. Atop the cabin, in the tabernacle, my aluminum mast soars heavenward -- or at least as high as a 22-foot mast will allow. At one time, I had a special lightning rod atop my mast, but I discarded that. It stuck up several inches higher than my VHF antenna, and that was a few inches taller than the tri-color running light I also had up there. Lightning, I figured, wasn't going to be that particular: it'd just pick the nearest tall object and shoot down it until it discharged. The lightning rod, I thought, probably wouldn't conduct the lightning any better than the antenna, or, for that matter, my metal mast, which in reality was the biggest lightning rod of all. I now had a basic path for a lightning strike's electrical discharge. If the antenna attracted it, it would zap down the mast, flip inside the cabin via the copper cable, and discharge harmlessly through the copper ground into the water. I also made the assumption that if I got hit that I'd lose all electronics. I figured it'd be a small price to pay to keep my boat afloat. And myself, unfried. As it turned out, I had reason to be concerned. The Florida Sea Grant study said that boats in fresh water suffer more damage by lightning than boats in salt water. Why? Because fresh water is a worse conductor of lightning's electrical charges. On Persistence, I needed some kind of zone of protection through a bonding system. This was because the tremendous voltage that came down the mast wouldn't just conveniently leave by my pre-arranged grounding system. Actually, in an electrical strike, large voltages can develop between metal parts in the boat - for example around the cockpit where the skipper and crew are - and this is very dangerous. I began tying in all metal parts of the boat into my ground. The way I did this was by crawling into all spaces under the cockpit, cabin and foredeck and adding an extra nut and washer to the through-bolted metal parts, such as the engine mount, stainless steel lifeline stanchions, winches, genoa track, through-bolted cleats and heavy chain plates and shrouds. In turn, these were wired to my grounding plate. Basically, this smaller wire became a horizontal ring of protection to bleed off electrical energy.

Now I was all set. If I couldn't totally "protect" my sailboat from a lightning strike, at least I had some grounding and bonding protection. This would divert most of the initial discharge and drain voltage away as much as possible. Besides, lightning never strikes twice. Or does it? An internet story came to my attention from a boater in the Tampa Bay, Florida area, who got hit three times by lightning. He figures a part of his problem was that his mast, at 63 feet including the VHF antenna, was the tallest in the marina. But he added that his boat had the tallest mast only by a couple of inches, and, maybe that wasn't the only factor. He filed three claims for the three lightning strikes, two of which were direct hits, for having to replace all electronics. A third claim was for a near miss by lightning, but still had enough voltage to burn up many of his electronics. The insurance paid out a total of $73,000 for lightning damage, and then failed to renew his insurance policy. Lightning factoids for sail boaters: Beware of cockpits: Basically, the cockpit is the most dangerous place in a sailboat that is not bonded because of its metal parts. For example, during a lightning strike, large voltages could zap a skipper big time if he or she had one hand on a metal steering wheel and, for example, the metal engine controls or the lifelines.

Head for safety: When storm clouds gather, head for shore. The worst place to be is on the open water where you and your boat are the tallest lightning rods around.

Try a little radio: An old sailboater's trick is to turn on an AM (not FM) radio to listen for static. This will tell you if there's an electrical charge building around you. Small, cheap portable radios are best.

Go below: If you do see lightning zaps too close for comfort, go below, if you can. That gets you away from all that metal in the cockpit.

Stay away: If you do go below, stay away from the mast-to-keel area. That's the primary route of the lightning seeking a place to exit.

Don't go near the water: Avoid any connection between yourself and the water. Your body is a better conductor than air, and lightning will like you better than air as a better route. You become a human lightning rod.

Worst-case scenario boat: The worst boat to be in during a lightning strike is a small sailboat in fresh water. Even if the boat has a well-built protection and bonding system, "it is still an exceedingly hazardous situation," says the Florida Sea Grant. If there is no lightning protection, the situation is "life threatening." In both protected and unprotected sailboats, advises the Florida Sea Grant, the places aboard to avoid are directly beneath the mast or the boom. Stay with the boat. If you think of going overboard, if you are in an unprotected boat, "electrocution is highly probable if lightning strikes nearby." In fact, says the Sea Grant, "there is no safe place on an unprotected small sailboat and in a protected boat only places of relative safety."

If the lightning factoids seem a little hard to take, take heart at Sea Grant's additional advice: "There is one place that is more hazardous than a small unprotected sailboat, it's a small, unprotected boat without a mast. Every year there are multiple deaths of boaters in open boats caused by lightning strikes, but there are very few reports of sailors in sailboats killed by lightning." Zap! One never knows, does one? Marlin Bree is a frequent contributor to Northern Breezes and is the author of four books about boating, including his latest, Wake of the Green Storm. (see www.marlinbree.com). His sailing adventures during Superior's "Perfect Storm" are included in a new nonfiction anthology from International Marine publishing, Treacherous Waters: Stories of Sailors in the Clutch of the Sea, garnered the publisher says, from "the best writing about sailing and the sea from the past 40 years."  

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Grounding the mast for Lightning Protection

• Thread starter John
• Start date Feb 14, 2003
• Macgregor Owner Forums
• Ask A Macgregor Owner

I'd like some input on how to ground the mast to achieve protection from lightning strikes. This is a real concern living in Florida as the rainy season ( with almost daily thunderstorms )is only months away.On most boats, the manufacturer goes to great lengths to run a big ground cable from the mast to the keel or a grounding plate and ties the battery ground, the engine and almost anything else that's metal to this ground. This forms what is referred to as "the cone of protection".I just acquired my Mac 26S and found that the mast isn't grounded. - Has anyone else made mods to get their boat grounded for lightning protection ?- If so, how did you do it ? Thanks, John  

Check out the archives try looking through the archives in the forum section, I found alot of information there, along with some good links.  

Thanks, you're right, but ....... Thanks Paul, You are right. There are a lot of posts about lightning protection & boats that have been hit, etc in the archives. There are many votes for doing nothing & taking your chances as well as many who profess to using diffusers, grounding plates, heavy wire, chains, jumper cables, etc I was hoping someone had come up with a way to quick connect/disconnect a 26S mast to some novel grounding system. I guess the closest approach I saw to achieving this is clipping a battery jumper cable (with a copper buss bar attached) to the shrouds and towing it in the water when thunderstorms threaten.It's not very pretty, but I guess it might afford some protection by providing a path for lightning to travel if the mast does get hit. John  

Lightning protection Hi John,Here's one of my favorite lightning information sites:http://www.marinelightning.com/science.htmThe other is on the related link.The concensus seems to be, if you're on fresh water, you need to find shelter on land. No amount of grounding in fresh water will prevent dangerous side flashes. In salt water, the mast, which is the best conductor on the boat, must be grounded to a 1 square foot or better grounding plate following recommended practices. All metal objects and electronics must also be grounded to the grounding plate.The reason everything needs grounding is that a lightning strike (even if not a direct hit) causes an electromagnetic pulse that induces high voltage spikes in nearby metal objects and electronics. If this elevated voltage is not drained off, electronics will be fried and crew will be injured or worse./_/), Happy sails,MArk  

Timm Miller

Chains during a storm......put some chains on you chain plates and let them dangle in the water. You can rig some jumper cables to the the same... make sure one end is in the water. This is not as good as a grounding system, but works when you get caught unexpected.  

John Dawson

prevention factor While I haven't followed the discussions on grounds for boats assiduously, I expected to see some advice that agreed with my best friend, a seascout-electricalengineer-exnavysub-nowNRCinspector who said (in my own paraphrasing) no little wire is going to channel a major hit. One of the primary reasons for trailing a wire of any dimensions is to prevent a difference in charge or potential between the masthead and surrounding area so it doesn't constitute a focal point. Conducting stray electricity is what most comments seem to address here. Is this how you understand it?  

Exactly It just lessons your chances........a direct hit, nothing can stop that. Now I heard while playing golf you can hold up a one iron because not even god can hit a one iron.......just something I heard.  

Lessening your chances ... So, the consensus says that grounding the mast just lessens your chances. Even so, that seems like a step in the right direction. Getting down to the practical side of doing this - Is anybody using a method more elegant than towing chains and jumper cables ? I'm thinking of something like a single conductor plug connected to a grounding bolt on the mast, plugged into it's mating socket next to the mast on the cabin top. Then a hidden large wire conductor that runs from the socket down to a through hull connection to a grounding plate (dyna-plate ?) that is attached to the hull somewhere away from the water ballast tank. The only concern doing it this way, is the corrosion that would build up on the ground plug and socket. Over time, this would make the ground less than perfect. Any other ideas or experience on how to do it short of using chains or a jumper cable ? John  

73mensailed

other archives I've read quite a few good articles with good links in the archives at sailnet.com. Just more ideas for you all.  

Jim Humphrey

Lightning line Check out the attached link. Some pretty deep stuff on lightning and boats.  

Jim's lightning Hey Jim,Did you mean this site?/_/),MArk  

Lightning Site Yes Mark, some had sent me that link last year when this topic was being discussed on the other Mac site.  

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Source: Ewen M Thompson.  Lightning and Boats, University of Florida Sea Grant.  www.thomson.ece.ufl.edu/lightning  

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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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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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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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• Sailboat Guide

Lightning is a 18 ′ 11 ″ / 5.8 m monohull sailboat designed by Sparkman & Stephens and built by Nickels Boat Works, Inc., Skaneateles Boat & Canoe Co., Helms - Jack A. Helms Co., Siddons & Sindle, Lippincott Boat Works, J.J. Taylor and Sons Ltd., Lockley Newport Boats, Eichenlaub Boat Co., Mobjack Manufacturing Corp., Clark Boat Company, Allen Boat Co., and Loftland Sail-craft Inc. starting in 1938.

Rig and Sails

Auxilary power, accomodations, calculations.

The theoretical maximum speed that a displacement hull can move efficiently through the water is determined by it's waterline length and displacement. It may be unable to reach this speed if the boat is underpowered or heavily loaded, though it may exceed this speed given enough power. Read more.

Classic hull speed formula:

Hull Speed = 1.34 x √LWL

Max Speed/Length ratio = 8.26 ÷ Displacement/Length ratio .311 Hull Speed = Max Speed/Length ratio x √LWL

Sail Area / Displacement Ratio

A measure of the power of the sails relative to the weight of the boat. The higher the number, the higher the performance, but the harder the boat will be to handle. This ratio is a "non-dimensional" value that facilitates comparisons between boats of different types and sizes. Read more.

SA/D = SA ÷ (D ÷ 64) 2/3

• SA : Sail area in square feet, derived by adding the mainsail area to 100% of the foretriangle area (the lateral area above the deck between the mast and the forestay).
• D : Displacement in pounds.

Ballast / Displacement Ratio

A measure of the stability of a boat's hull that suggests how well a monohull will stand up to its sails. The ballast displacement ratio indicates how much of the weight of a boat is placed for maximum stability against capsizing and is an indicator of stiffness and resistance to capsize.

Ballast / Displacement * 100

Displacement / Length Ratio

A measure of the weight of the boat relative to it's length at the waterline. The higher a boat’s D/L ratio, the more easily it will carry a load and the more comfortable its motion will be. The lower a boat's ratio is, the less power it takes to drive the boat to its nominal hull speed or beyond. Read more.

D/L = (D ÷ 2240) ÷ (0.01 x LWL)³

• D: Displacement of the boat in pounds.
• LWL: Waterline length in feet

Comfort Ratio

This ratio assess how quickly and abruptly a boat’s hull reacts to waves in a significant seaway, these being the elements of a boat’s motion most likely to cause seasickness. Read more.

Comfort ratio = D ÷ (.65 x (.7 LWL + .3 LOA) x Beam 1.33 )

• D: Displacement of the boat in pounds
• LOA: Length overall in feet
• Beam: Width of boat at the widest point in feet

Capsize Screening Formula

This formula attempts to indicate whether a given boat might be too wide and light to readily right itself after being overturned in extreme conditions. Read more.

CSV = Beam ÷ ³√(D / 64)

One of the most popular one-design classes in the US since the 1940’s. But fleets also exist in other parts of the world. Although originally designed for wood planked construction, nearly all boats since the early 1960’s have been built of fiberglass. Ballast above is max weight of centerboard.

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Netball turns over a new leaf as 2024 season looms

Analysis Netball turns over a new leaf as 2024 season looms

Forgiven, but not forgotten, as The Corrs once sang.

It's hard to measure just how much damage last year's Super Netball CPA negotiations did to the sport so soon after the fact, but the athletes themselves hope the ordeal hasn't turned fans away from the sport.

Gathering in Sydney for the 2024 Super Netball launch a day after it was announced Netball Australia chair Wendy Archer would be stepping down, each of the eight team captains acknowledged last year had been extremely tough – as domestic players went unpaid for 11 weeks in the lead-up to Christmas and the tense battle over a revenue-share model played out publicly in the media.

There have been a range of controversies in netball over the past three years, but this issue seemed to be the straw that broke the camel's back. People were fed up.

Former Australian World Cup winning captain and coach Joyce Brown labelled the CPA stoush as the sport's "lowest point", blaming its executive for fracturing "the fabric" of the game and "irreparably damaging" its relationships.

Meanwhile, Australian netball legend Liz Ellis also called out the administration for its "callous disregard" in its treatment of players and questioned if Netball Australia was "capable of providing the leadership the sport so desperately needs".

Once a deal had finally been struck in December – rewarding players with the very first revenue-share model in history, as Netball Australia waved the white flag  – chief executive Kelly Ryan was the first major casualty after a two-and-a-half-year stint at the helm; citing the "time was right" for her to move on and spend more time with her family.

Three days later, it was a quiet departure for director Marina Go, who had been on the board since 2017 and previously held the role as both chair of the Super Netball commission (now defunct) and Netball Australia, before stepping back in late 2022 in the wake of the Hancock Prospecting saga.

Now, the news of Wendy Archer's departure shows the aftermath of last year is still being felt.

Many pundits had been calling for a full clean-out, which felt unlikely, as it was only three months ago that Archer held a press conference where she told the media that the board had been prepared to continue supporting Ryan as CEO; it was Ryan herself that had made the decision to leave on her own terms – unbeknownst to the board; and that no further changes to the executive had been discussed or were expected despite mounting pressure.

Instead, Archer said the immediate priority was to work with all stakeholders, not just the players or the players' association, but all of them in order to "heal the sport and move forward".

This press conference was held before Go's departure, which was only made public mid-January, and before two new figures joined the board in 2024, signalling the acknowledgement at least that they understood some change was needed. Yet, the news this week of Archer's departure still comes as somewhat of a surprise.

Archer has played many pivotal roles in netball, particularly in the state of NSW, where she is a life member and was a key figure in the Giants' bid to join the Super Netball league.

Although there were questions about whether she was a strong enough figure to lead netball through such a messy period, she is well-respected and well-connected, which makes it even more interesting that she has now made the decision to move on.

Her departure will not be swift, as the relevant press release explained that Archer will no longer be the chair from May's annual general meeting onwards, but will stay on for another year as a director until her three-year term ends to ensure a smooth transition for the next chair.

Other parts of the release to note, include the phrases: "now is the right time to step down" and "the Netball Australia board embraces renewal and a fresh injection of ideas".

The first sounds rather familiar to Ryan's announcement, while the second feels like a complete 360-degree turn to the goals and priorities discussed with the media by Archer in December, when the board was resisting change and unwilling to take responsibility for its poor management.

Either way, netball now finds itself on the hunt for a new chief executive and chair. These appointments will be crucial to the future of netball in a very important World Cup cycle, with Sydney set to host the next event in 2027.

At least all parties will be moving forward in a proper partnership and working together from now on, with that revenue-sharing model in place.

"Unfortunately, netball has been in the headlines for negative reasons more so than positives in recent times," Sunshine Coast Lightning shooter Steph Fretwell (née Wood) told ABC Sport.

"At a Diamonds level, that negative side of what was happening overrode our success winning gold at the Commonwealth Games and World Cup.

"But change has happened, it's now in the past, we need to learn from it and move forward by making sure we get the right people in those positions and invest in the right areas."

Meanwhile, West Coast Fever midcourter Jess Anstiss had a different take, suggesting the negative attention may actually have enticed people to take an interest in netball.

"In a way I think it has helped us," she said.

"There's that saying, 'no media is bad media' and some of my family members who have no idea about netball are now talking about the sport after everything that happened.

"It involved more people in the conversation and helped people understand what was going on behind the scenes, so although those last couple of months were especially damaging, people are now asking how they can help – including sponsors."

Queensland Firebirds and NSW Swifts veterans Kim Ravaillion and Paige Hadley weren't so sure the controversy had had that type of effect, hoping loyal fans had kept the faith but worrying new ones may have been scared off.

"Fans that really love the game and want us as women to succeed and get what we deserve – they are probably going to stick by us and hopefully they can see why we stood strong," Ravaillion said.

"The people that are embedded in netball, it probably wouldn't turn them away, but we're trying to attract new people and sponsors, so when the sport looks messy then that is tough," Hadley said.

"We're now just trying to look forward to the future and focus on what we can do as players to make sure the game is in a good state."

This weekend the pre-season Team Girls Cup will take place in Sydney, where fans will get their first proper look at brand-new incoming team the Melbourne Mavericks.

Captain Amy Parmenter said although the drawn-out negotiations had led to a shorter pre-season, rushing preparations, players were now looking forward to playing a season focused on their on-court performances, without the same kind of pressure hanging over their heads.

"It does feel like a new era, because we're going to have new leadership, and the relationships are definitely repairing, so it feels like a fresh start," Parmenter said.

Tune in to the Team Girls Cup from Friday at 4pm AEDT on Fox Netball.

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