We have a beagle and he loves to go for boat rides. He gets excited when I even approach the "Boat Bag."
If you want to go out for relaxation and 'getting away,' I'd leave the dog at home. I don't know anything about your dog, but ours' can't sit still for very long and like to run around and play so he's only good for short periods of time. He definately comes along when we go to the island or somewhere he can hang out, though.
If you can figure out how to make him/her go do his/her thing off the swim platform, let me know. We can't seem to convince ours' to.