Re: radio on jet ski
There is a reason they don't come with one... Hint, whats the easiest way to sink a jetski... Cut some big holes in the hull, and then cover them back up with pieces of foam, paper, or very thin plastic. (aka a speaker)
Seriously, if you tried it, you would stand a very good chance of sinking it the first time it was rolled over. Even on an extremely stable big jetski, a rollover can still happen. When it does, the water pressure will be more than enough top pop a speaker in, and dump ALOT of water in almost immediately.
Also, you will be letting tons of engine compartment noise out now, the speaker would be unusable while driving obviously, but your ski would also sound obnoxious to everyone around.