[LIforrelaxin]

All great suggestions here, but I figure you are all missing the mark, if your going to have a swim raft capable of weekend adventures, 120V or 240V really doesn't matter, what you need to be sure of is that you have 100Amp service, and hey just so you don't have to worry about expansion why not go with 200Amp service.... You will not have to worry about how many hair dryers, are in use, or radio's etc. In fact with that kind of upgraded service, you could install an incinerating toilet, for convenience...

Now as has been brought up by others, some swim noddle conduit should do the trick for getting the wire out to the swim raft, and should have the added bonus, should someone be ignorant enough to be boating between your dock and the swim raft to provide a wonderful firework show anytime of the day. If your lucky they will have been fishing and you will get a well cooked fish fry.

But wait there is more, Just think you could put up some high intensity Halogen lights, to keep your shore front nice and lit up from the raft. After all you don't want the lights on shore because they will attract Mosquito's and the like. That way all your guest will be safe as they watch their kids safely from shore, and you will not have to worry about them tripping do to poor outside lighting, and a twig that has just fallen.

Last you just need to make sure that the connection goes directly to the transformer on the mainline, this way you will not have an accidental circuit breaker failure, when something goes wrong.... I mean those fuses on the poll must be good to a couple of hundred amps, before they fail......