I am still playing around with yachts on the internet.
So I am reading a nice little book about little boats, what I call “Bass boats” as an unscientific name. The book says to head in at the first sign of lightning. I can understand that. A little toy boat on a lake is likely to get zapped and has no protection.
But I have no idea if a proper power yacht is lightning safe. Are they? How is this done? Are the electronics safe after a strike?
My neighbour has a 40ft yacht and before I realised that I was never going to conquer sea sickness I used to regularly accept his invitations to go sailing. One time we (4 of us) were planning on sailing from Brixham to Plymouth, round the tip of south Devon, UK, and there was a thunderstorm forecast. I did some reading, because I was pretty concerned about it, and there is all kinds of anecdotal clap trap out there, the most jarring, to me, being some imaginary “cone of protection from the tip of the mast downwards”. I can’t remember where I read that, I think it was a yachting forum. Equally, there were abundant horror stories about yachts getting hit and people dying.
I went anyway, and sure enough, the thunderstorm appeared. We followed the coast about 7-10 miles offshore and all took turns driving the boat. The storm was the MOST SPECTACULAR FREAKING THING I’ve ever seen. Forked lightning hitting the sea around us, obviously not that close, but with no reference points it does look spectacular. You only really know how close the hit was when you hear the thunder. My neighbour and his son, both experienced yacht people, were not concerned in the slightest. Whether we were just lucky I don’t know, but it sure does seem to me that the huge aluminium mast poking up in the sky is the only thing for miles around that it likely to get hit.
Maybe that cone of protection thing wasn’t so imaginary then… I’m off to try and find out some more.
Oh, boy! This could get to be a regular Pandora’s can of worms. 
Or maybe not. The ABYC has its set of specs, and a dozen other sources have their own ideas.
For a couple of decades, I saw a variety of answers in SAIL magazine and Practical Sailor. I didn’t keep track much, because I had a small fresh water sailboat, and I didn’t sail in storms.
Linking together the mast, electrical ground, prop shaft, and a big fat through-hull ground plate might be the right lightning answer, but it might cause electrolytic Hell that will eat your prop or your keel.
Some swear by leaving the mast unlinked, but in a storm they wrap a chain around the mast, and dangle the other end in the water.
There was even a tale of a lightning strike that blew the foot-square ground plate right out of the hull. Fortunately the yacht was docked at the time.
A lady I knew well on the gulf coast of Florida said her 32 foot yacht was struck while docked, and the only damage was a fried marine radio.