The one subject in marine electrics where the experts genuinely disagree with each other, the standard got downgraded, and half of what is sold to prevent it has no evidence behind it. Here's what is actually known, what isn't, and what we think.
This page is a discussion, not advice. We are not electrical engineers and we are not surveyors. Lightning protection is life safety, and nothing here should be used in place of a qualified marine electrician who knows your boat.
We're publishing it because the honest state of this subject is "nobody is certain", and almost nobody says that out loud. If you know better than us on any of it, please come and say so — that is the entire point of the page.
Physics doesn't have opinions
A lightning strike is an enormous current — tens of thousands of amps — looking for a path to ground, and delivering the whole lot in microseconds.
On flat water, a sailboat mast is often the tallest object for a long way in every direction. That is not a theory, it's geometry, and it is why sailboats are struck far more often than powerboats of the same size.
| Figure | Roughly |
|---|---|
| Chance of a boat being struck in a given year, US average | about 1 in 1,000 |
| In a lightning-prone area such as Florida | about 3.3 in 1,000 |
| US lightning deaths per year, all causes | around 100 |
| Of those, aboard boats | around 13 |
Those are insurance-claim and national figures, not our numbers. Read them properly: the odds in any one year are small, and the consequence is severe. That combination is exactly the kind people are worst at reasoning about.
And this is a bigger area than the industry admits
This is the detail that tells you everything about the state of the subject.
The American Boat and Yacht Council published lightning protection as a standard, and then withdrew it, republishing the material as TE-4 — a Technical Information Report. Informational. Not a requirement.
A standards body does not downgrade a standard to a report because the subject is well understood. It does it because the evidence won't support telling people there is one right answer.
TE-4 is still the best starting document there is, and if you are building a system it is what to work from. Just know what it is.
Bonding means connecting all the large metal aboard — mast, engine, tanks, through-hulls, rails — to a common conductor, so nothing is at a wildly different potential and the current has less reason to jump sideways.
The counter-argument is that you have just wired every piece of metal on the boat to the thing most likely to be struck.
The consensus leans towards bonding, with the important qualifier that bonding on its own offers no protection unless there is a good direct path to ground as part of it. Bond everything to each other and nothing to the water and you may have made things worse. That much is widely agreed.
What size, what route, what counts as "good" ground on a fiberglass boat with an encapsulated keel — much less agreed.
The familiar idea: a grounded masthead protects a cone beneath it, so anything inside the cone is safe.
It's a rule of thumb borrowed from land-based practice, the angle quoted varies, and the physics underneath it is far shakier than its confident appearance in diagrams. Treat it as a planning aid, not a guarantee, and be sceptical of anything that claims your cockpit is inside it.
You can buy a bristly stainless brush for your masthead, sold on the theory that it bleeds charge off the rig fast enough to stop a strike forming.
There is no independent evidence that these prevent strikes. Several well-funded research efforts have looked at the concept and failed to support it, for boats and for buildings. A static dissipator cannot prevent a lightning strike.
A softer version of the claim does circulate — that a dissipator makes your mast slightly less likely to be the thing that launches the upward leader, so the strike goes somewhere else. It is a form of camouflage rather than a shield. Even that is argued over.
We are not telling you to take yours off. We are telling you not to plan around it, and not to skip a real grounding path because you have one fitted.
Erik's own view, clearly labelled as opinion
What follows disagrees with the mainstream advice on this page. I know that. I am not an engineer and I am not telling you what to do with your boat. This is what I actually believe, written down honestly, and I would rather argue about it than pretend I agree with something I don't.
The standard advice is: give the current a deliberate path to the water. My instinct says that by building that path, you are putting your hand up.
Here's how I see it. An ungrounded fiberglass boat has nothing electrically reaching up into the sky. As far as the storm is concerned you are part of the water — there's no conductor standing up, no path through you to anywhere. You are close to invisible.
Bond everything, run heavy copper from the masthead down to a plate in the sea, and you have changed that completely. Now there is a conductor standing sixty feet above the water with a direct route to ground underneath it. You are no longer part of the sea surface. You are the tallest grounded thing for miles, and you have built exactly the path a strike is looking for.
| Grounded and bonded | No path at all | |
|---|---|---|
| Chance of being struck | Higher. You've invited it. | Lower. Much lower, I think. |
| If you are struck | Better odds of the boat and the people coming through it | Worse. The current makes its own way out and takes the electronics with it. |
| What you're really choosing | Accept a strike, survive it | Avoid the strike, pay for it if you're wrong |
That's the choice as I understand it, and I genuinely have not made up my mind. Both positions have a real cost and I don't think anybody can tell you honestly which one is right.
The figures at the top of this page say roughly one boat in a thousand is struck in a year. I don't think that number means what people take it to mean.
Most boats do not have a proper grounding path. Very few have been built to the standard, and plenty that claim to have one have a bonding system that goes nowhere. So the low strike rate is measured across a fleet that is mostly ungrounded — which, if my reasoning holds, is exactly why the rate is low.
Take the small number of properly grounded boats and work out their strike rate on its own, and I suspect it would look very different. I have never seen anybody publish that figure. Until somebody does, the headline number is comparing a mostly-invisible fleet against itself.
I could be completely wrong about this. The counter-argument is reasonable: your mast is tall and conductive whether you bonded it or not, so the grounding changes where the current goes rather than whether you get hit. I understand that argument. I'm just not convinced by it.
Credit where it's due
My thinking on how lightning actually behaves came mostly from other people's work, and one channel in particular.
The one to watch
Reversing Entropy is my go-to source on how lightning behaves — the physics of how a strike actually forms, rather than the usual list of boat advice. If you only watch one thing on this subject, watch that.
Thank you for making it. A lot of what is on this page is me thinking out loud about what you explained properly.
Here are all three, on the creators' own channels. I don't agree with every word in all of them and I'm not telling you they're right — take them or leave them. They're here so you can see what I actually watched and make up your own mind rather than taking mine.
Reversing Entropy
Start here. This is the one that changed how I think about it — the physics of how a strike actually forms and why it goes where it goes, rather than another list of boat advice. Everything I've written above is me reasoning from what he explains here.
Clark's Adventure · Capable Cruising Guides
The practical cruiser's take — what to do about it on a real boat, and what happens afterwards. Closer to the mainstream position than mine, which is exactly why it's worth watching alongside the others.
Epoxy and Butyl Tape
Somebody actually building a grounding and bonding system into a boat, on camera. If you're going to go the grounded route, this is what the work looks like rather than what the standard says.
Sources, and the ones we find convincing
Everything above came from reading and watching other people's work. We'd rather point you at them than have you take our word for it — especially on a subject where we have just spent a page telling you nobody is certain.
The Technical Information Report on lightning protection. The starting document, and the one your electrician should know.
Ewen Thomson's research and published papers — one of the few people who has studied boat strikes specifically rather than adapting building practice.
Independent testing, no advertising from the people they review. Their lightning coverage is the most honest in the consumer press.
The insurance claim statistics quoted on this page. They see the actual outcomes, which almost nobody else does.
Trade journal rather than consumer magazine. Written for people who build boats, so it assumes you can take the engineering.
The avoidance half — storm structure, forecasts, and real-time lightning data. Free, and more useful than any hardware.
That's what this page is for
We would rather be corrected in public than quietly wrong for years. If you have been struck, if you fit these systems for a living, or if you think we've got a section of this backwards — come and say so.
Strike stories are genuinely valuable. There is very little published data on what actually happened aboard, what survived, what didn't, and what the boat had fitted. Every first-hand account is worth more than another article repeating the same advice.
Exodus