Some soapy water, a heat gun should get you mostly on your way. May need to use some goo-gone of some kind and something to scrub (not scratch) after you take the surface layer off.
The more slowly and evenly you can peel, the better off you are in getting the tape off. Try to pull at almost 180 degrees from the way the tape lays on the surface - if you see what I mean, don't pull 90 degrees away from the boat hull. Try to pull the opposite direction along the hull so the tape is folding back over itself. Make sense?