The definitive answer isn’t in for lightning protection on a sailboat. It isn’t even clear how all the damage is done by lightning, nor what type of lightning we are trying to protect from. Any time there are many ways to do something, it means that either anything, or nothing works well enough.
The basic concept of a simple lightning rod, with a direct connection to ground, has worked very well for centuries. (Possibly until we started to have phone and electrical wires going into buildings?) Since the early 1800's the British Navy very successfully prevented damage from lightning strikes on wooden sailing ships, with wooden masts by using an iron rod and iron wire from the mast tops to the water. Nobody has proven any benefit over these simple systems, in spite of all the hype of the lightning rod salespeople.
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Per a report on lightning by BoatUS Seaworthy:
“(1) It is better to avoid being struck in the first place, but (2) if your boat does get hit, you will suffer less damage if the strike is grounded as directly as possible.” >>
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What I plan to do isn’t far fetched, and is relatively simple, and cheap. It may not protect from every type of damage, from every type of lightning, and it may work better with a catamaran.
> >I want to keep the lightning out of the boat! Give it a simple, direct route to ground, without connections, angles or upward angles, which encourage side deflections. Don't encourage it to hit the mast, and then try to minimize the damage.
Use 4-10 G insulated copper wire, stranded. The size may depend on mast height, and your anxiety level. Run it through and attach it to ½ inch PVC pipe, and hoist it by a halyard (spinnaker, main, spare jib, or topping lift) attached to the PVC. This is to add rigidity (and further insulation where the wire is closest to the mast near the top). The wire is secured inside the pipe with a wad of electrical tape.
The top 2 feet or so of wire should be above the highest antenna, and the top foot of insulation would be removed and these wire strands, above the antennae, could be:
- splayed open,
- pointed, or
- rounded (preferred)
In an almost straight run, the wire would stretch from above the mast head, through the bow netting to the water. This is not close to any electronic equipment, or metal. The insulation is removed just above the water, and the wire strands are splayed and run into the water for at least one to three feet, to allow better grounding and dissipation of current. This would be more difficult to set up when sailing, but not impossible. On a monohull, the wire could go over the lifeline, through another piece of PVC pipe.
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Granted, even 2 G wire wouldn’t protect completely from a direct lightning strike, but the goal is to get the lightning out of the boat, not just to give it more benign route through it. Then hopefully the cone (or rolling sphere) of protection will protect the occupants and equipment.