I have float tubed in King's Harbor a few times, but it's not my preferred method of fishing there by any means. I do not believe there is actually any restriction against them, despite what the harbor patrol may tell you. From a safety standpoint, it makes sense that they are discouraging people from tubing there. As it is, guys in yaks, inflatable rafts, skiffs, etc. are constantly fishing in the main channel and around the pier, getting in the way of passing boats. Tubes are less visible and maneuverable, and would be even more of a hazard. Then you've got the sea lions to deal with, and it's really not worth it. Rent a skiff (expensive) or get a small craft - you'll be a lot happier.