According to the Boat Owners’ Association of The United States (BoatUS), the chances of a boat lightning strike in any year are about one in 1,000.

Although these odds are less in the UK, it does still happen.

Anyone whose boat has been hit by a direct lightning strike will tell you it’s the loudest bang they’ve ever heard.

It can leave your ears ringing for half an hour and leave you confused and in shock.

Be prepared to hand steer your
boat as your electronics will either not work or can fail at any time. Credit: David Harding

Because some important steps will need to be taken immediately to prevent further damage, it’s helpful to have a checklist ready.

The huge current surging through the boat can char things in its path but also generates currents in metal objects around it.

The intense heat can cause air to expand and blow things apart, even things made of plastic or wood.

The trail of damage can go anywhere through a boat and often has no logical path.

Boat lightning strike checklist: Storm approaching

Protecting electronics 

• Putting electronics in the oven is a good move. Most ovens aren’t a proper Faraday cage, which will protect the contents. Microwaves are better protection if you have one on board but an oven is still better than nothing.

The massive current of a strike generates an electromagnetic field which generates secondary currents in wires throughout the boat.

Many sailors try to protect their electronics by putting them in the oven, although a microwave will offer better protection. Credit: Graham Snook/YM

Anything plugged into a long charge cable or with an antenna (VHF, Bluetooth, wifi, GPS) is at risk of creating damaging currents inside the device.

Unplug as much as you can.

Communications

You’re likely to lose your VHF antenna if your boat suffers a direct strike, so make sure your handheld VHF radio is charged, ready for use. Credit: David Harding

• There’s no way a VHF antenna will survive a direct strike. You’ll be lucky to find any traces of it.
• Unplugging your VHF cable as you hear the storm approaching will help protect the radio unit, but it won’t mean you have a working VHF after the storm has passed. If you’re going into stormy waters keep your handheld VHF radio and backup navigation tablet charged, but unplug them when you feel at risk.
• You can give a position report over the radio to neighbouring shipping as the storm approaches and ask for a call back in an hour, but remember that if swapping from a mast antenna to a handheld your effective range will be reduced significantly, and other crews will be having their own thunderstorm issues to wrestle with.

Safe space

• Stay inside, and away from the mast and other electronic devices. Damage to the boat is bad enough, but exploding shrapnel can injure the crew.

Boat lightning strike checklist: Immediately after a strike

Immediately after a strike check for Fire, Float, and Fire-up. These are three essentials that will help prevent escalating damage.

Isolate all devices except the bilge pump. A lightning strike can blow out through-hull fittings. Credit: Duncan Kent

• Firstly look in each cabin and on deck to check for any fire. Electrics can burst into flames and it’s important to catch it quickly to prevent a fire from spreading; bear in mind you may need to abandon ship if the fire has taken hold. It’s not unusual to have a cabin full of smoke from fried electronics but this doesn’t mean there is a fire.
• Isolate devices to make sure they aren’t shorting and risking an electrical fire, but keep power to the bilge pump.
• Secondly, check to see if there is any water ingress, or if the bilge is filling. Lightning can blow out through-hull fittings, leaving a gaping hole. It can also burn through the hull leaving small pinprick holes which can fill the bilge more slowly. If the bilge pump is cycling on and off it means it is keeping up with any leak. If it’s constantly on then you’ll either need to find and plug the holes or supplement the pumping with the manual bilge. Or prepare to abandon ship.
• Finally, check the engine fires up. Knowing that you can motor will give you more options. Older diesel are pretty resilient to lightning but batteries and starter motors can get fried. Newer engines which rely on an electronic control unit (ECU) are very prone to dying in an electrical storm. Your outboard is much more likely to have survived than the ECU so consider if you can tow the boat with the dinghy.
• If at anchor you’ll also need to know if your windlass is working so test it by letting out a few links. Pulling up a chain by hand may not be safe in stormy conditions.
• Keep an eye on the bilge as the rate of water inflow can build up.
• Make sure no one has been injured and reassure the crew that you are all safe and have survived being hit by lightning. You may have to treat people for shock.

Check the voltage reading of your batteries; if it is low, there’s a chance they have been damaged. Credit: Graham Snook/YM

Boat lightning strike checklist: Morning after

Passing 300,000,000V through your boat can cause damage to every and any system.

• Try to figure out the path of the strike through the boat. Has it travelled down the mast into the keel or along the headstay and into the anchor chain? Understanding this will help you identify where to look for further damage, but secondary currents generated in wires around the boat can create confusing clues. For instance, if it went into the keel check to see if the glassfibre between the mast and keel is leaking water. If it went down the forestay, has the chainplate or tang been weakened?

Rigging

• An aluminium mast is a good conductor and will generate comparatively little heat but stainless steel rigging is less conductive and the heat created can be enough to weld and weaken the cables. A rig check is a good idea to make sure the tangs aren’t showing signs of heat damage. Similarly, the chainplates need to be examined. The frustrating thing with stainless steel is that it gives few clues as to its internal state but looking at the glassfibre around it can reveal if has been affected by heat.

Electricity bill

• Circuit boards tend to blow fuses, diodes and melt solder tracks. Sometimes these can be repaired, but most professionals won’t even attempt to repair lightning-damaged electronics. Even electronics that are working immediately after the strike can give up the ghost within a few months because of weakened solder tracks. Do a full systems test. Course computers are very susceptible to blowing, as are AIS boxes and VHF radios that haven’t been unplugged from the antenna. Be prepared for hand steering until you can fit replacements.

Charged up

• Batteries will usually make it clear immediately if they’ve been damaged with a low voltage reading, but charging sources like alternators and shore power chargers also need to be checked as they’re very susceptible. Draining the battery without a charger can also damage your battery over the next few days so check you have current going in.
• Inverters, either because they have large coils inside or the thick wiring runs, are prone to failure. They tend not to drive critical systems but will mean your power tools are out of action for any repairs.
• Wiring can ted together causing slow drain short circuits but it’s rare. Mostly it conducts current to devices that feel the damage. The longer the wire, the more likely it is to generate an oversized secondary current. Look for unexpected spikes in current draw as you turn on isolator switches one at a time. This will indicate a problem in the wiring loom.

Check the windlass is working by letting out a few links. Credit: Graham Snook/YM

Chilling

• Fridge control units are also susceptible to failing, sometimes in an always-on state; make sure you’re not unnecessarily freezing your food and draining your battery.

Pump it

• Despite having a big coil inside, pump motors tend to fare well in a strike. If they aren’t working, check the switch relays first. The coil in relays, unlike pumps, is very prone to failure. Get comfy with your multimeter, you’re going to be spending a lot of time together.

Lights out

LED bulbs will likely blow following a lightning strike. Credit: Graham Snook/YM

• LED bulbs have a very weak resilience to electromagnetic shock and you may find that even if they were off when you were struck, they have failed. Check individual bulbs before starting to chase wiring looms around the boat.
• Your navigation and anchor lights are unlikely to have survived if they’re up the mast. Keep in mind that other boats may not see you, especially if your AIS is out of action too. It’s your responsibility to light up the boat so you aren’t a hazard to shipping. If there’s traffic, improvise.

Transducers

• The wind transducer may look intact but it’s unlikely to work after a direct strike. Even a nearby strike can knock them out. Most models have an internal printed circuit board (PCB) which can be replaced at a fraction of the cost of replacing the whole unit.
• If the strike exited through the hull transducers, speed or sonar, they can be fried too, even though their internals are very simple.

Insurance

• Surveyors won’t risk their liability and often state they cannot guarantee a given system is reliable after a lightning strike, so if your insurer covers lightning expect them to replace everything, even stuff that works. Claims for a strike can easily reach £50,000, but the excess on electronics means you’ll still be facing a bill of a few thousand pounds.

Expert opinion

Electrician Adam McMenemy of ACM Marine says: “My personal experience of a boat that got hit by lightning is as follows: The boat was a 64ft Trader motorboat, wired correctly, grounded to special ground plates. Following the strike, there was no damage to the actual boat but the VHF antenna was split and burned. There was no fire or explosion, but all of the electrical equipment was killed, even things that weren’t attached directly to the boat, such as multimeters and handheld VHF radios; all were completely dead. All bilge pumps, motors, chart plotters, lights, in fact anything with a circuit board, had to be replaced. The cost of the damage was £39,000.

“The insurance company stated it was an Act of God and didn’t pay out. It’s also worth remembering that jumping into the water could be fatal if you are on board a boat in fresh water and a lightning strike happens. This is because fresh water doesn’t conduct electricity (unlike salt water) but people do. If the fresh water has been electrified by a boat or other machinery leaking voltage then a human in the water could be electrocuted.”

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