Boating and yachting - With more than 30,000 A (amperes) located in an arc, the effects of lightning on a ship's structure can be formidable. But not all boats are created equal!

Metal, wood or composite hulls and sailing boats take the impact very differently.

In this second part of our lightning dossier, we look at the structural damage caused to boats by lightning.

Lightning can strike a boat directly, attracted by an aerial, mast or any other metal appendage. The electric arc then strikes the metal conductor directly and works its way through all the conductors in its path. 

But a boat can also be affected by a secondary effect of lightning striking the water. When lightning strikes the water or the ground, it creates a very localised potential difference at the point of impact. This difference is sufficient to create transverse arcs between the point of impact and a nearby conductor. And all ships contain conductors. 

These transverse arcs, although they have lower currents, are still capable of inflicting serious injury on an individual and serious damage on a boat.

Metal hulls at an advantage

Like cars, metal ships behave like a natural Faraday cage in thunderstorms and lightning strikes. Wherever the lightning strikes, the highly conductive metal masses that make up the superstructure and hull harmoniously transmit the current to the sea. Electric fields cannot enter or leave the ship, at least in theory. A theory that corresponds to reality, because the electrical insulation of metal ships is always particularly meticulous when it comes to their electrical and electronic installations. Metal habitables are the safest when the crews are inside, without contact with the hull.

Wooden ships contain thousands of air bubbles trapped between the wood fibres. If the hull's watertight barrier is no longer in good condition, micro-pockets of water mixed with wood decomposition products will form between the fibres. The impact of a lightning bolt and the transmission of the very high current (several tens of thousands of amperes) will cause the materials it passes through to react differently depending on the resistance they offer. In the path of the lightning, the air contained in the wood will go through a plasma phase likely to cause its structure to shatter, and the rise in temperature (30,000°C) will do nothing to help. 

Exotic wood deck coverings on metal yachts or poorly protected composites can literally shatter if struck by a bolt of lightning.

The highly combustible resin-fibreglass composite that makes up most yachts behaves particularly badly in the presence of lightning. This is why sophisticated protection systems are installed (4th article in our series). In the presence of a transverse arc and a metal through-hull, for example, the current will melt the material around the through-hull. The degree of melting depends on the strength of the current.

The following images show various structural damages on wooden or composite hulls.

Next :

Lightning 3/5: Damage to electrical and electronic circuits