How to best prepare for thunderstorms and lightning aboard?

What’s the worst that can happen at sea?

Some of you may have witnessed that surreal moment, which halted all America’s Cup racing on Tuesday.

Following our travels, we’ve often been asked the above question. And that picture perfectly illustrates our answer.

In most cases, some wind and waves shouldn’t be a problem for a properly handled seaworthy boat. Hence Ready4Sea.

But thunderstorms are a different story altogether. They are too small in scale to predict reliably. And, in our mind, the random nature of lightning strikes makes them the ultimate danger – and both skippers aboard Emirates Team New Zealand and Luna Rossa Prada Pirelli seemed to agree!

A few things can be attempted if caught out in such a situation, but on the whole it’s best avoided at all costs! We’ll also brush on how you can protect your boat and gear.

Preserving the boat out in a thunderstorm

When caught out in a large thunderstorm, the sole objective is to preserve the boat and the crew.

Traditional advice is to use the anchor chain to create an electrical link between the mast and the water. The beneficial effect here is twofold :

1️⃣ In the case of a lightning strike, it will provide a clear path for the current to flow between the top of the mast and the water. If no guidance is provided, electricity will find its own way, including through materials normally considered to be insulators, such as a fiberglass hull. The trouble is this will most likely melt it, thereby causing water ingress and sinking the boat.

2️⃣ Creating an electrical contact between the mast and the “ground” (i.e. the water) is the best way to ensure the potential atop the mast is as close as possible to that of the water itself. This greatly reduces the likelihood that lightning will strike the boat.

Of course, in the case of a metallic boat, there is no need to use the chain since contact is likely already made.

Preserving electronic hardware during a thunderstorm

Yet, let’s be honest, if lightning strikes and the boat does survive, be aware that everything electronic aboard will be toast and your compass may be off. This means no more VHF(Very High Frequency) Radio wave frequency band, between 30 and 300 MHz. By extension, the most widespread marine radio sets, operating on a series of predetermined channels between 156 and 174 MHz, with a range of a few miles to a few dozens of miles. radio, no more GPS(Global Positioning System) Satellite positioning system with worldwide coverage, enabling users to determine not only their latitude and longitude, but also their heading and speed., no more autopilot, etc. And perhaps even no more lighting aboard.

Nearly the same also happens when the strike happens close by, because the intense electromagnetic field is lethal to the very sensitive electronic hardware. Metallic boats have a slight edge here, because they create what is known as a “Faraday cage”, which shields the inside from what happens outside. Obviously, in the case of a direct hit aboard, the result will still be the same, though.

Yet, let’s think about that Faraday cage concept once more. Most cruising boats have some kind of oven onboard, which metallically shields its content on all but one side. Anything placed in there is more likely to survive than outside. Of course it’s not big, but there is room for a handheld compass, a portable VHF(Very High Frequency) Radio wave frequency band, between 30 and 300 MHz. By extension, the most widespread marine radio sets, operating on a series of predetermined channels between 156 and 174 MHz, with a range of a few miles to a few dozens of miles., a portable GPS(Global Positioning System) Satellite positioning system with worldwide coverage, enabling users to determine not only their latitude and longitude, but also their heading and speed. and a headlight. By the way, if your boat is the kind that sports a microwave oven, that’s even better because it is built for the purpose!

To further enhance this protective system, we always had a tin box aboard. In the event of a thunderstorm, we would replace its content by the above critical items and place the tin container in the oven. That makes for two nested Faraday cages. You could even create a third one by wrapping your items in some aluminium foil. The goal, here, is that after a lightning strike there is some chance that some or all of them may still be functional.

Protecting the boat in thunderstorm-prone areas

Now, despite these tricks, quick reminder: avoiding thunderstorms is the best advice. And for this, you should study and understand the weather patterns in your area. Yet, some people sail in places where thunderstorms are just too common to be avoided (like Panama and many other equatorial regions). Plus, lightning might strike while not underway or not even aboard, like that unlucky Boston boat a few years back.

What is the best course of action then? How can you protect your boat from lightning?

Well it turns out that there is no way to prevent lightning strikes. But there are ways to provide a safe discharge path for the current to flow through in the event of a strike, as discussed above. You can just make this permanent if the occurrence of thunderstorms in your area is too great. Your insurer will likely know 😉

This involves installing grounding plates, copper wire, and even lightning rods or “dissipators” atop the mast – although the effectiveness of the latter has yet to be proven. All of this will provide a clear conducive path for the current to flow. As for the electronics aboard, some surge-protectors are available and may be installed to protect costly and/or essential gear.

Do you have any other tips to share with other mariners? Please message us or react on our social media so we can update this article.