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What to do in a thunderstorm at sea


Damage from lightning strikes to pleasure craft at sea or in marinas is more common than some would believe. For this reason, every skipper must pay close attention to this issue.
Damage to the yacht itself, accessories, equipment and personal injury are possible due to incorrect behavior during thunderstorms.

Even if the lightning strikes nearby, rather than directly, the electrical and electronic components of a yacht can be irreparably damaged by overvoltage.

You cannot protect yourself from a lightning strike on your yacht. You can reduce or possibly avoid damage.

Motor and sailing yachts made of steel

Due to the design, you have a continuous electrically conductive connection from the top of the mast to the steel hull.

This provides optimal lightning protection according to Faraday’s principle. However, fuel tanks must be connected to the hull of the ship with good electrical conductivity so that no fire or explosive discharge sparks jump over in the event of a lightning strike.

Yachts made of wood or fiberglass with a metal keel or a metal sword

On sailing yachts, lightning will probably always strike the mast, shroud or stage and discharge itself. These are only suitable as lightning rods if they have a diameter of at least 6 mm and are electrically connected to holding points on the deck and to the metal keel or sword.

If there is an aluminum mast, a conductive connection between the base of the mast and the metal keel or sword is sufficient.

If protective measures were not taken during the construction of a yacht, it is difficult to install suitable lightning protection afterwards.

More makeshift could be: “leash-over-board method”

At the lower end of the shrouds or stays (at least 6 mm diameter), an 8 mm thick copper or stainless steel cable is attached to both sides of the boat with a special clamp. Both ropes must plunge into the water at least one and a half meters outboard.

It is better not to use temporary fasteners instead of the special clamps available from specialist dealers. If there is a lightning strike, it can cause a spark to jump over at defective connection points between shrouds, stays or ropes and cause fires.

Alternatively, complete lightning rods consisting of a copper rope at least three meters long and a suitable clamp can be purchased in stores.

In an emergency it is possible to use the anchor chain, if available, as an arrester. It should be wrapped around the forestay several times and lowered into the water.

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  • Avoid staying on the water with an open sports boat during thunderstorms.
  • Thunderstorms are often associated with gusts or strong winds. Prepare yourself for these weather phenomena in good time.
  • Never stand on deck during a thunderstorm.
  • Keep hands away from metal parts, do not touch shrouds, stages or other metal objects such as railing.
  • If possible, switch off electrical devices and disconnect them from the mains.
  • Do not go into the water for a swim during a thunderstorm.

Get advice from a specialist company who is familiar with lightning protection systems on board ships and yachts.

It’s about your safety and the safety of your crew.

Damage from lightning strikes can cause major damage to a yacht due to the existing electronics.

Lightning damage to a sailing yacht, time of damage: May 2019 LP: Baltic Sea

Extract from the expert report:

During the inspection, the general condition and damage could be recorded as follows:

• There are clear traces of a lightning strike in the mast top of the yacht.

• The HF antenna and the Windex on the mast top are missing or have been damaged.

• There are significant charring on the VHF cable at the deck passage.

• No damage to the standing rigging from the lightning strike was found on the rigged ship.

• The stern light on starboard aft has “exploded”.

• None of the instruments on the operator’s platform are working.

• The LEDs on the inboard switchboard of the yacht have been destroyed by overheating.

• All instruments and devices in the navigation area have failed.

• The voltage converter and the charger are destroyed.

• The electric windlass does not work.

• The engine’s alternator has been checked, it does not charge, but the engine itself is working properly (apart from the displays on the engine instrument).

The necessary repair costs are provisionally subject to further damage: € 29,104.79

Always observe the rules of conduct during thunderstorms or storms. If possible, avoid thunderstorms widely!

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