|In his excellent description of his cockpit sole rebuilding, Roger Gibb makes reference to a probable electrical "leak" from his boat into the surrounding water. Coincidentally, there is a warning in this month's Ocean Navigator magazine about the danger of such leaks. Apparently this was highlighted by the drowning of a teenager this summer and near-drowning of his friend.
Both boys were swimming in a marina and obviously there was stray current in the water that paralyzed one; the other was injured but managed to get far enough away to save himself. Counter-intuitively (at least to me) the danger is greatest in fresh water. Salt water is a uniformly good electrical path, so stray currents just go to ground. Fresh water is a lousy conductor, so electricity finds a better path through people. Zap, you're fried.
The expert advice is, don't concern yourself with how good a marina or club is at managing its electrical service. Even if it may normally be a safe environment, all it takes is a new boat with a problem and zap, you're fried. Don't swim anywhere (in marinas or clubs, or near dock walls) where boats are or may be plugged into shore power.
C&C 27 Mk IV