Marine Lightning Protection

Marine Lightning Protection

Marine Lightning Protection

Have you ever wondered what is the best protection from lightning when out at sea? We take a look at the specific challenges, the magnitude and frequency of energy involved, the risks to consider, and how to mitigate them. If you missed it, you can watch a replay of the Marine Lightning Protection webinar here.

Hello, and welcome. Thank you all for coming.

For those that are new here. My name is Ian Griffiths, I’m the Principal Consultant here at GreyMatters. We’re passionate about protecting life from the harmful effects of high voltage, which in this case includes lightning. That’s either by design in what we do on a day-to-day basis, but also in the seminars by education.

So, the series of webinars that we do is, we try and unpick topics that don’t have obvious answers. And today, as the title suggests, we’re covering marine lightning protection. Interestingly, in researching this, there’s an amazing lack of material out there covering this topic. So hopefully, we aim to unpick some of the principles and an awareness point, way. So, let’s dive in.

  • Facts & figures
  • Basic theory of lightning
  • Marine context
  • Options
  • Standards
  • Discussion – Q&A

So, one of the tenets of GreyMatters is if we can save just one life by what we do on a day-to-day basis, then that’s a massive win, and we would have succeeded.

Another reason where lightning is dear to my heart in the marine context is that next year, I happen to be competing in the Fastnet 2023 race. This is my boat Black Betty.

Black Betty

I’ve got a personal vested interest in understanding about lightning and how it can affect race boats, particularly. But yachts, boats, offshore, anything like that.

Lightning Stats

It’s claimed that over 300,000, ground strikes hit the UK shores each and every year. Now, this is data extracted from 1999. So, it’s about 20 years out of date, to be honest. So, we can safely say that this is conservative. Given that climate change and the warming of our planet is going to have a massive effect on these numbers over the next coming years.

An interesting number that I wasn’t particularly aware of was that nearly 50 people, on average are struck in the UK each year. Obviously, this compares to a 10th of what happens in the USA. But you know, the states are such a larger territory, that that would be understandable.

Marine Lightning Protection - Lightning facts

In terms of fatalities a year that are attributable directly to lightning. It’s on average 3 in the UK, a year. Now, the HSE statistics suggest that 4-7 people die a year from the construction industry, so this is to give you comparison. So, it’s not insignificant by any stretch of imagination. And it usually takes about 12,000 strikes before somebody gets struck. And then if we extrapolate that further, then the fatality rate is looking at 1:100,000.

Now interesting figure for me is the ratio between male and female. And why is it that males are more prone to being struck by lightning? I don’t have an answer for that. Maybe you do. And that certainly we can cover in the discussion later.

Theory of lightning

Okay, so let’s look at theory, the process behind lightning itself.

Static Electricity

Lightning can be considered as a discharge, how the charge is generated is something like this…

I think we’ve all been here. You’re even when I walk in the office each day. It’s about 30 meters on this nylon type of carpet. And by the time I reached the office door, I know that I’m going to get a little charge, discharge when I touch that door and what’s happening there is build-up of static Electricity.

So that is the engine if you like behind lightning.

Cloud formation

So here is an extract from the RYA Yacht Master course and theory course and categorizes nine types of cloud formation that we are interested in when we’re out in the ocean.

The one of particular interest for the lightning point of view is the Cumulonimbus here. It’s the one that crosses the largest elevation, it crosses all layers, if you like, of the atmosphere.

Cloud Formation

And what’s happening here is that the thermal energy is taking the moisture and raising it up through the column into the upper atmosphere. And as it does that, the temperature levels are dropping significantly. This is then causing the moisture to form into ice crystals and snow crystals, which then collide against one another.

And this process of colliding against one another, it creates, the charge builds up in static charge to start to occur. And they start to shed and separate their charge.

Charging cycle

So, if we look at the charging cycle in more detail, here’s our Cumulonimbus. Which is in the classical anvil form, where you’ve got the lower layer, and the lightning core, which is where most of the lightning happens. And the charge then starts to separate as it rises through the column. What we end up with is the start of a storm cell where the concentration of negatively charge ions appear on the underbelly of the storm cell. And positively charged ions sort of rise to the top. This happens in majority of cases, 80-85% of storm cells are negatively charged on the underbelly.

There are circumstances where this is reversed, but I won’t go into that in detail in this session.

Field Intensity

But interestingly, what it sets up is a field intensity. Which induces a charge of equal and opposite charge as a shadow if you like, on the ground on the surface.

Field intensity

Now, the field intensity between the two charges is as a function of elevation. So, for every meter of elevation, the field intensity increases by 30,000 volts, on average. And this is why, you know, taller structures are more susceptible, more vulnerable to lightning.

Upward Leader
Upward ladder

So, you get the shadow charge on the surface. It also starts to charge up the surrounding structures, when it could be trees, blade of grass, towers, light towers, and this control tower, to the point where you get saturation happening and the charge then starts to hop on to air molecules and you get this leaching of ions into the air. And if the path is saturated enough, you get the forming of an upward leader.

Downward Leader
Downward ladder

Lightning is a competitive event, which means that there are competing other sources of upward leader which are also suffering the similar kind of charging process. You then get a downward leader. Which is a concentration of negatively charged ions start to make its way, track its way through the air towards the Earth. And it reaches its last step leader here.

Point of discrimination
point of discrimination

There’s a key moment in time where it reaches a point of discrimination. If it were sentient, it would start thinking about what is appealing to me the most. Which structure here is sending up the most attractive streamer that I can latch on to.

It’s not obviously this is physics, and it’s just a case of you know, who’s providing the most saturated ions, it’s giving the most forces of attraction and it will latch on to. So, if this one over on the left here is sending up most amount of ions and intensity, then it will track horizontally to make that connection.

And I’ll come on to this a bit with these standards. But this is this has significance this radius or point from the point of discrimination.

So, in this case, it’s latched on to the control tower. What happens next is a massive surge of current up from the ground as the ions flow into the storm cell. And they then equalize and return.

It’s this return stroke that we see with our naked eye. Because the upward stream as they happen so fast that it’s too fast for the human eye to capture it. Whereas what we see is that downward return stroke. Where most of the current then starts to transfer and discharge into the ground.

Lightning discharge

Okay, so I mentioned lightning core before. Lightning core is where most of the lightning happens. And as the storm cell recharges, each time it discharges, this can take sort of 10-15 seconds typically, before the next strike happens, it can be longer. And you know, the longer it takes, the weaker the storm cell. The shorter the time duration, the stronger the storm cell is, and the more concerned you need to be.

So, this is where predominantly you might get in scrolls and stuff like that offshore.

Bolts out of the blue

But there is another phenomenon, which is bolts out of the blue.

This happens when the field intensity is such that it grows to such an extent at the higher altitudes that we see the discharge happen at the higher level of altitude.

The problem is with this is that the levels of charge are massively more. We call these bolts from the blue. They cause disproportionately more damage, because they’re just seemingly come out of nowhere, and their intensity is much greater. And up to 15 nautical miles from the core. So, they can appear very random indeed. So don’t get too close to lightning cell.

What do the standards say?

In terms of standards, and how we can characterize this. Now, Lightning has many, many personalities in the form of its frequency.

A lightning strike can contain multiple frequencies, anything from DC, single frequency right up to hundreds of megahertz, and everything in between. So, it makes the maths complicated, and arduous.

Marine Lightning Protection - Standards

To simplify, what the standards tend to do is to normalized into the typical lightning parameters of an impulse, wave form. And it’s been characterized under 62305 as a 10/350 microsecond waveform. So, what that means is that if for argument’s sake, it’s typically takes 10 microseconds for the rise time, before the it reaches its maximum amplitude, and then decays to a 50-percentile point, which typically takes 350 microseconds. So that’s how the standards characterize a lightning impulse for our maths calculations.

It does vary, lightly in the real world does vary massively. Which means that to do thorough analysis of lightning, you need to actually study many multiples of lightning frequencies. But to simplify things, we talk about the 10/350 Waveform as a single waveform.

If you’d like to dig deeper into the subject of lightning and how to model a lightning strike, then I encourage you to take a quick look at the previous webinar on modeling lightning in our library. Click here to view our webinar replay library.

But in terms of the standards, these are the kind of the typical figures that we work with. Which means to say in Europe we see 80% of the strikes with around 20 kiloamps or less and some that go as high as 90-100 kilo amps.

What does this mean?

Bringing this back to a practical point of view. If you’re on the ocean and you hear a thunder crack, or and see lightning or lightning flash and then hear the thunder crack then count the number of seconds it takes from the flash to when you hear the sound. And as a rough rule of thumb, if you divide that by three, you then arrive at how far away that storm cell is away from your vessel. And if it’s less than five seconds from the flash, buckle up, you’re in for a ride.

Equatorial waters will naturally see more lightning activity than anywhere else. And this is largely down to the fact that thermal energy is the driving force behind lightning. It’s that force that drives the moisture, up the column of the Cumulonimbus into the upper elevations and where the charge separation process can begin.

Equatorial water map

So, this is why we see the activity here on zero latitude, it peaks around zero. Interestingly, most strike activity actually happens onshore, not offshore. So that should be a relief to mariners alike. But it’s still pretty significant in the tropics, and something to be aware of.


So, reviewing what we’ve looked at, we’ve covered

  • Build up of charge (Static) > Transfer/Discharge
  • Current direction starts from ground > cloud (mostly)
  • Outdoors is most dangerous
  • Bolts from the blue
  • ~80% cloud-to-cloud
  • Most lightning classified as first negative strokes
  • <200 KA
  • Multiple frequencies (DC-MHZ)

So that’s a little bit about lightning.

Marine context

Now, let’s put this into a bit of a marine context.

We can see that you know, some of the larger vessels are 10s of meters high. And this as we know with the field intensity growing at 30,000 volts per meter, puts vessels with masts, blades, cranes towers at risk, for sure. Because of the isolated nature, when compared with the rest of the surface.

Now fortunately, the sea is a low resistivity medium, so it does actually naturally suppress lightning from propagating from the sea surface. But it is incredibly hostile terms of corrosion. And we know that vessels, offshore platforms at anchor are very well grounded. They’re very well earthed in this low resistivity medium. In terms of an anchor, it’s literally grounded, physically. We know that equatorial waters see much more lightning activity around the equatorial waters than at the higher latitudes. And the stats also bear out that the frequency which is the NG (the number of ground strikes) is generally higher onshore than it is at sea.

What are the standards?

So, in the UK, the relevant standard that we look at as the go to standard is BS EN 62305. A standard tries to provide guidance to the widest possible applications imaginable. And the problem with that is it’s trying to be all things to all people and whilst it does a phenomenal job in onshore protection. The offshore side of things hasn’t had the same input.

From a practical point of view. It’s che case of extrapolating what the measures are and what the guidance is on an offshore and basically transferring that across to the marine environment the offshore. So, you have to be apply a little bit of engineering judgment and transfer, what’s been said on the onshore side of things and migrate it across.

Lightning Risk

And the process is loosely around assessing the risk.

Marine Lightning Protection - Rolling sphere modelling
Rolling Sphere Modelling

First, and looking at, if you recall the point of discrimination. Now the point of discrimination then gets transferred into the standard as the rolling sphere, or radius of rolling sphere.

So, you can see this would be your last step leader, and it would pointed discrimination, it would start then to look at what surfaces it can attach to. And in this case, it’s the forestay of this yacht.

But we can roll this imaginary sphere, all around the yacht’s surfaces, and see where these points of vulnerability are. So, we look at the risk and where the lightning attaches.

Location Flash Density (Ng)

We also look at our passage where we’re going to in terms of location and the density. The flash density that we might encounter, during that passage.

Souls onboard

We may also look on the occupancy of the vessel on a cruise liner with 8000 people, then receiving a strike to the vessel would send a lot of people into absolute panic. And that has to be considered as well.

Size & Scale

If you’re like me, you’re on a 30-foot yacht, compared with a cruise liner, then there’s, there’s definitely differences in vulnerabilities.


And finally, we might look at the construction. And I think we’re going to look at that in a little bit more detail now.

Lightning current paths

Marine Lightning Protection - Lightning current paths

So, on my yacht, for example, it’s a glass reinforced fiber hull, so it’s non-conductive above the waterline. So, these are all the conductive surfaces that a lightning strike might attach itself to that we need to worry about. Below the waterline, we’ve got the keel and the propeller.

So, the current paths for typical yacht would be these metal shrouds, the mast, the boom, and these would discharge through the keel. And maybe it’s got its own Earth plate attached with everything bonded back to it and discharging into the ocean. And this is where it gets a bit sticky with vessels. So the majority of the lightning current might get discharged into the ocean. But there’s also going to be a portion depending on the frequency of the energy and try and find a path through the electronics. And that is really what kills the navigation and electrical systems on board.

What can we do?

We know onshore we got surge protection as a common method of mitigation. But if we’re sailing, or we’re on passage somewhere, we’re not going to have that shore connection. We’re basically on our own. In all honesty, if you’re talking about a small sailing vessel on a 12 or even 24-volt DC circuit, then the choice of surge protection device is quite limited. So, it’s a balancing act, do you invest significantly in the protection when it might actually outweigh the cost of actually just replacing the damaged components? It’s a tricky one.

And I think it’s because of the sheer amount of energy that they have to deal with, these surge protection devices are actually quite small. They’re either very small spark gaps or metal oxide resisters, which can’t take very much energy before they fry anyway.

There are options available. I would say probably that they provide some degree of protection, depending on the size of your vessel, and where you’re going to be operating in.

If you’re a large commercial, offshore vessel that operates at say $200,000 an hour, it’s going to be a massive risk to interrupt that in any way. So actually, putting surge protection in those kinds of scenarios makes perfect sense. Especially if operating, for example, in the Gulf of Mexico, or other equatorial waters where he knew you’re going to be seeing a lot of lightning.

When connected to shore

When I’m connected to shore, I like to think that marina or shore-based operator is being diligent with their surge protection. Because that can provide us with a much more practical degree of protection from surge. Having the boat sat in electrolytic solution (the sea), we’ve got to be mindful of effects of enhanced corrosion.

This kind of example setup would actually protect you very well, from a lightning strike nearby lightning strike to the onshore.

Metal Construction

Okay, so for metal constructed boats, the considerations are different.

You’ve obviously got metal hull, metal superstructure, and everything is likely to be commonly bonded naturally. And if it isn’t, then it’s not a big ask to actually formally bond bits of equipment so that they are all at an equipotential level.

What to do…

So, this brings me to okay, what should we do? What measures should we do? What options do we have?

These are the three things to take away from today:

  1. Equipotential Bonding (check regularly) – You can look at equipotential bonding onboard. Make sure that everything is commonly bonded to a single point. Which is in yacht maybe the keel, or an earth bar near to the keel, or an earth plate that’s on the hull, if it’s nonconductive construction. But check that the joints haven’t got corrosion, and that there’s good continuity between the parts.
  2. Do NOT touch anything metal – If you’re in the middle of a scroll, or a lightning event, offshore, don’t touch anything metallic, if you can avoid it.
  3. Avoid being on-deck – Better still avoid being on deck at all in the elements and get yourself down below. And even down below, try not to touch too many things metallic, as you could see a portion of lightning current as it passes through. So, you don’t want to do that.


Risk Assess

Take a look at your own situation. Risk assess where you’re going to be operating in, take a look at your vessel, take a look at any occupancy, take a look as many things as you can. BS EN 62305 does offer a good framework to actually do a formal risk assessment. Albeit it’s not specifically for an offshore environment, it does provide the framework to do it sensibly.


We haven’t gone too much into the options for mitigation, but they include equipotential bonding. But making sure that the conductors that you use are sufficient to withstand that lightning current for a start. There’s no point putting your four-mil supplementary green, yellow wire, it will fry like fuse wire, if it’s anything like the lightning currents that we’ve been talking about here. So, making sure that they’re sufficiently adequate to cope with direct lightning strike. There is guidance in the BS 62305 that covers that.

Mitigation might also be considered some kind of actual air termination on your vessel. If it’s particularly large commercial vessel, it might be worthwhile actually considering where lightning attachments should actually happen and try and manage that process as best you can.

There are some options which rely on charge transfer technology, it’s aimed to suppress the precursor for a lightning strike. Now in order for CTS (charge transfer systems) to work efficiently, there needs to be a density of points and I’m not going to cover that in this session. But for your average kind of yacht or leisure craft, you’re unlikely to have the surface area to be able to deploy sufficient points to suppress any precursor of a lightning strike. But for your much larger vessel platforms then these can also be an option to consider.


From there you can self-protect, don’t put yourself in danger in the first place. If you do find yourself above decks in the middle of a storm, then try not to touch the metallic parts of the boat that could become energized.

Adjust according to passage

And review, adjust your risk assessment according to the passage that you’re making. If you are taking in equatorial waters, then really ramp up your measures accordingly.


Okay, so hopefully that’s raised a few questions and uncertainties. Like I say that at the beginning, there’s a severe lack of material out there and content covering lightning protection in the marine context, which is interesting in itself.

The systems that are typically on sort of leisure yachts, they’re either sort of 12 to 24 volts. And navigation equipment is super, super sensitive to over voltage. Which is why the surge protection can struggle, because of its size. The kind of lightning currency it has to deal with, it might be okay for the first hit, but then subsequently can’t deal with multiple hits after that.

Having been in multiple scrolls for that matter, all you can do is cross your fingers as you go through. Hope that it’s not you that the lightnings going to find and attach to and that you can get out the other side unscathed and continue on.

This is very much part one of marine lightning protection. In 20 minutes, we can’t really hope to cover everything. So, it’s just a quick dip and that the questions that come out of this will inform another session to dive deeper.

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