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“ How to Protect from Lightning Strikes on a Boat ? ”

A lightning strike is a strong electric discharge in the air, accompanied by a bright light (lightning), and a loud bang (thunder). Material damage caused by these lightning strokes occur on a regular basis, but the largest risk is that of electric shock. Everybody knows what to do if you are on land, but how are you supposed to react when you are on a boat?

Foudre sur un bateau

What attracts a lightning strike: power lines, metal, any electric conductors, high points or very high objects. Lightning always tries to strike the earth the fastest way possible. On a boat, lightning protection means that there must be an uninterrupted connection to guide the current of the lightning towards the water without causing any injuries to man and animal, or damage the hull or any electronic equipment.

Important notice: for boats longer than 24m that were built after 1993, standard ISO 10134 applies and demands for an installation of lightning protection by the manufacturers.

You are aboard a metal boat : A boat entirely made out of steel or aluminium is quite naturally well protected against lightning. If the boat is struck by lightning and you are inside the boat, the metal will lead the electricity around you and not through you. Be careful not to touch anything made of metal so that no electricity can flow through your body.

You are aboard a polyester boat : The risk is fairly low. If there are one or several objects made of steel on the outside, it is advisable to connect them to the water (using the keel if it is steel, or the anodes).

You are aboard a boat with a mast : A boat mast is a point very often struck by lightning (same as a lightning rod). If the boat is not equipped with a lightning protection system, you can create a predetermined passage way to make sure that there is a perfect connection between the mast and the water. This enforced passage way prevents the lightning from searching for its own explosive path which might lead through fibre glass, teak wood, or members of your crew … You can, for example, place part of your anchor chain round the mast foot, connect the chain to the shrouds, and plunge the end of the chain (about one metre) into the water. Alternatively, you can choose to fix a metal tip onto the top of your mast as a lightning rod, and connect this tip to a bolt on the keel, using copper braiding in between.

The probability of a lightning stroke can be less, depending on the landscape and on the environment (buildings, trees, …). A boat that is cruising or anchoring on a large water body will, for example, find that it is more exposed to the risk of being struck.

In any case, if you are facing a violent thunderstorm on board, here is some advice: disconnect antennas or similar items, avoid using any electronic equipment, and wait in the interior of the boat. We strongly discourage you to go into the water, since severe bodily harm is very likely if the lighting strikes somewhere nearby.

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