How to protect a boat against lightning strikes

Lightning Strikes  Thailand

Well guys and girls if you get a hit like this one, nothing can save your boat, or if it survives then the electronics are definitely dead.

However, you can mitigate the possibility of this happening. It’s quite easy to do and not expensive.

First of all, why does lightning hit one mast and not another even if the mast next door was higher?

Well first of all, let’s look at one possibility as to why. This is my opinion and there are plenty of others out there as well. Lightning Theory seems to be one of the dark arts.

If we go back 30 to 40 years to how cars were in those days, you would remember that sometimes when you opened the door you would get a static shock. This was due to the tyres being all rubber and electrically isolating the vehicle from the ground. Nowadays the tyres have carbon or other conductive material in them to dissipate the charge down to the ground.

As the air moves over a mast and rigging, it attracts a static charge, which slowly builds over time. If the mast and hull are not grounded, and especially if they are non-conductive Fibreglass –  and not self grounding Steel or Alloy, an electrical charge builds.

When an electrical storm builds a charge in the atmosphere the charge wants to get to ground by the least resistive path. An un-grounded mast attracts a static charge and it is also the highest point thus it tends to be the least resistive path. The lightning ‘discharges’ to ground via the mast with all the high voltage, (and resultant heat), passing through the boat and it’s equipment if its in that direction of flow.

This electrical isolation also may be a reason why fibreglass boats, and especially catamarans, get hit far more often than steel or alloy boats.

On a lot of fibreglass boats the rigging is not GROUNDED to the water. This happens a lot on catamarans. A bonding wire from the mast’s base to a VERY good grounding plate in the below water part of the hull is imperative.

You may find that lightning has not hit your boat directly but some damage is still caused by the high voltage dissipating to ground and causing a voltage ‘spike’ in the locality. Often this ‘indirect’ or ‘side’ strike can damage electrical equipment with no outward signs of damage on the boat.

So what to do to reduce the risks of being hit directly or indirectly by lightning, so that the risk to your boat is as low as possible?

  1. Ground the mast at it’s base and the rigging at multiple points where they attach to the hull, (this is best done at the forestay, the mast base and the rear backstay) down to a large grounding plate that’s in the water. This ground plate needs to be large and preferably of a sintered material which increases the surface area that is touching the water (the bigger the better).
  2. Do not ground it to your motor as engine mounts and oil are insulators. If you do get a strike it may damage the main bearings in the motor and/or the gear-box bearings as it passes to ground through the metal shaft and propeller.
  3. At high risk times it does not hurt to also add extra points from the rigging into the water as well.  ie a wire from the forestay to the anchor chain or to a hanging anode.
  4. The idea is to get the rigging to be as close as possible to the electrical potential of the water around you and reduce the mast’s electrical attraction to Static Electricity in the atmosphere.

Now we come to the Electrical gear on board.

Damage to all the electrical systems onboard can be by direct and also indirect or ‘side’ strikes. 

In a direct hit, like the one in the picture, the high voltage passing through every system will destroy electronic components and even wiring. There is not much that can be done to prevent damage, However a lot of people are keeping essential items (Phones/Hand held GPS etc.) in a Faraday cage (this will protect these items from EMP) and maybe also let the voltage passes around and not through the equipment. A microwave or oven may be useful as a makeshift Faraday cage in times of a lightning threat.

If however you were a boat next door, or 500mtr and even up to 2Nm away, you could also have damage caused by an electro magnetic pulse (EMP). A lot of damage is being done from side strikes especially in marinas and busy anchorages.

An EMP is a strong magnetic pulse produced by a lightning strike, which imparts an electrical charge along the wires in your boat even though the strike is some distance away.  This voltage spike within the wires themselves, causes damage to the electrical items in the boat. Navigation and other electronic items are particularly susceptible to this effect.

You can prevent EMP damage from side strikes by installing surge diverters, (or by putting items in a Faraday cage)These devices stop the voltage rising over say 16 volts on a 12 volt boat or 32 volts on a 24 volt boat by opening a contact to ground within milliseconds – before the voltage spike can cause damage.

These devices should also be installed in each different electrical circuit ie. on the 110/220 volt systems (both the Generator and the Inverter AC systems), and each of the boats 12/24 volt systems (both Starter and House Battery Banks).

Octopus has a lot of experience providing quotations for lightning strike insurance claims and dealing directly with insurers on your behalf.

Side strikes and the resultant EMP damage is often not easily identified. The damage to electronic components can be subtle and sometimes not lead to immediate failure – making insurance claims difficult.

As prevention is better than cure we would recommend fitting Novaris Surge protectors

These voltage diverters are easy to fit and provide peace of mind to you and to your insurers, that the best possible protection has been given to your electrical and navigation equipment.