As an Electrical Engineer
in a former life with some knowledge of lighting protection for explosive ordinance factories... I can say that lighting is a scary thing and not always well understood.
One poster asked about attaching a copper wire to the chainplates and running it into the water
... Probably not a good idea. Lighting protections has two major factors... prevention and damage avoidance/dissipation if hit. The overall best protection from damage from a lightning strike is the development of a Faraday Shield basically an encompassing series of conductors that envelope the item to be protected. Some feel the standard metal rigging
on a sail boat would provide a somewhat effective Faraday Shield but it is far from ideal... or even good. With the Shield the lighting would strike it and not the protected item. Problem is the application/ design of the Faraday Shield. Difficult on land and even more difficult on a boat. What a Faraday Shield dose is raise the probability of strike to be on an engineered element where it is attempted to direct it to a discharge path that would less likely harm the protected item.
Two though paths exist on this subject. One is Actually moving the Ground potential to a high point above the protected item which would be like having deep rods attached to heavy copper lines which attach to numerous lighting rods around the protected item... the down side is you would Attract more hits than if none existed... you never hide under the tallest tree on a golf course type thing. However if the bleed-off engineering were good most of the damage potential would hopefully be abated. Some designs actually have active elements in the lightning rods to polarize them so that they will attract at a higher level than simply ground.
The other method is having a similar protection grid that is detached from a ground signal or has an active element that would make the lightning rod appear less desirable until a strong potential is detected by sophisticated detection equipment
then and only then would it be switched to attractive potential. These systems use more of a Spark Gap type theory. Where if hit the lightning would jump a small gap to reach ground but the small gap would prevent the elevated lightning rod from appearing to be a more ideal target.
Lots of people have played around with the spark gap approach in boats and it seems to work in test conditions but not as well in real life conditions in ocean environments. The major problem being that the gap effective is defeated in a salt water environment
when the gap is expose to it or its spray or just general salty environmental conditions. Some companies have developed a sealed spark gap but the same problem occurs when the exterior of these sealed units are salt
encrusted or simply getting spray when a strike event occurs.
Bottom line is that is appears Cats are struck more often due to the damn fur on them than sea dogs
in "real boats"....
In real life we evacuated the munitions plant when ever lightning strikes occurred within a 4 mile radious... not very practical in any sail boat.