Below, I go into a little more detail about what happens when a sailing boat is struck by lightning and what you can do to prevent that. Not much data about lightning strikes directly talking about vessels being hit by lightning.
Boats can get struck by lighting and are most likely to do so if caught in a storm at sea. Lightning tends to strike the tallest object in its vicinity, and boats are the most elevated objects on the sea. So boats, particularly those with masts, are essentially giant lightning rods.
According to U.S. insurance claims data (from BoatUS Marine Insurance), the odds that a boat will be hit by lightning each year is around one per 1,000, rising to 3.3 per 1,000 in areas with a high frequency of lightning strikes, like Florida. Sailboats and powerboats are the boats that are hit by lightning most often, according to BoatUS, the odds being 4 per 1000 for sailboats and 5 per 1000 for powerboats in general. They say your chances of getting hit by lightning in a thunderstorm are slim.
It is unlikely that your boat will get hit by lightning but keep in touch with your insurance agent in case it does. These are the best options and tactics to follow, but if that happens, and you are on a boat hit by lightning, talk with each other right away to make sure everyone is okay.
Boating During a Lightning Storm Is a Horrible Decision
Hopefully, that will motivate you to stay on board the boats and provide the necessary information for safely making your way through the lightning storm, should you have to. Then, being the only boat out there during the lightning storm would increase the odds of being this one out of 10,000. You already know the odds of being struck by lightning even in the first place.
The best way to reduce the damage from lightning is not to be hit by lightning. You cannot stop lightning from striking your boat, but a properly designed and engineered lightning defense system is the next best thing. Knowing what to do during a storm, and having the best possible lightning protection installed on the boat, is not at all a guarantee that lightning will not strike. You will not place a literal cage around the ship to protect it from lightning.
Lighting strikes your boat will take the path of least resistance. Your boat will be small enough for lightning to continue down that path. Sometimes, lightning has nowhere else to go once it hits your boat, so it will punch a hole through your hull and come out this way. Even though you cannot visually see the damage, it does not mean when lightning does exit your boat’s hull, it does not cause a small gap that will start leaking water and sinking your ship.
The Mast Is Effectively a Lightning Rod
If your mast is not grounded correctly, the impact of a lightning bolt could very well result in an electric potential difference just ripping a hole through your deck or hull to escape into the surrounding water. Having a lightning rod mounted to the top of your mast, connected to the earth, is an excellent place to start, but having a lightning rod attached to the highest spot on your boat is insufficient to protect against lightning adequately.
To dissipate the current from a lightning bolt in freshwater, you need a far more comprehensive system of grounding underwater than is typically found in protected boats. The idea behind a grounding system is to direct a lightning current along a set route to prevent it from taking an explosive course through the fiberglass, teak, crew members, etc. Figure 4 shows what might happen if lightning strikes an ungrounded fiberglass boat with an aluminum mast.
Lightning strikes the masthead and loads all the Riggs; a boat must have a conducting path to direct the load into the water. If the sailing ship and a Jon boat are placed next to each other in the water, lightning strikes the sailing ship every time.
The situation is far more complex in freshwater because the electricity involved during the lightning is approximately one thousand times greater than what occurs on the saltwater boat. The damage is far more significant to vessels struck by lightning in freshwater than ships hit by salt water, as fresh water is a poor conductor.
Open Boats Are the Most Dangerous of All
An open boat such as a skiff is most dangerous for human life in a lightning storm, as you are at the highest elevation and most likely to get stuck in your boat if struck. If yours is the only boat in the area during the lightning storm, your chances of getting struck increase dramatically, leaving you and your crew vulnerable to millions of volts descending from the skies. Much of your boat’s wiring is likely to get melted entirely by the lightning.
On an unbonded boat, high voltages will build up between the mast, the chain plate, the tree stump, the stern stay, the wheels, the rudder posts, the bow rails, electronics, and wire harnesses, reinforced metals in the plumbing fixtures, the engines, etc. These can make working the boat extremely dangerous, even when no lightning strikes the ship directly.
Cruiser friends who have experienced a lightning bolt on the boats they are sailing have agreed on one thing; a bolt is so violent no ordinary lightning shielding would work because the electrical energy is so vital it leaps up in the air and can hit metal objects, sometimes up to 20cm.
As it is on land, being struck by lightning on a yacht is quite unusual and unlikely. According to Boating Lightning Protection from the University of Floridas William Becker, you are better off running for safety than remaining out in the open, as long as you can get back to shore and take cover in a vehicle or enclosed structure getting caught on the beach.
Insurance provider BoatUS statistics indicate that multi-hulled boats are twice as likely to be damaged by lightning. The British and American-based insurance companies also reported that multi-hulls are between two and three times more likely to suffer a lightning bolt than monohulls because of their increased surface area and lack of a keel, which causes difficulties in grounding correctly.
Protection A standard system for protecting against lightning is to have a rope (lightning bar) over the vessel connected with the thicker cable running underneath and an underwater metal ground plate attached to the hull — larger metal objects such as tanks, engines, and tracks are also connected.