If their was a preventative way to decrease lightning striking a boat, the insurance companies would be all over it.
But... but... but... there is no way to "prevent
" lightning strikes. The best that can be done is to try to reduce the potential damage in the event of a lightning strike.
What I find interesting in your situation, is that the lightning struck tower a 100 yards away, and then traveled through the water, entering your boat, proceeded up your mast, and hopped to the neighboring mast. Makes for a curious electromag fields theory problem.
Importantly, it gives rise to the question, how does one protect their boat in that sort of scenario? After all, the papers I've read, thus far, seem to only account for direct lightning strikes as opposed to your situation.