First - dont discount on a marina. They are typically an assache deluxe. Will it be a common feed? Typically no. Is it a condo group of slips or what? Be prepared for a little more engineering than just a few amps. I'm sure you'll need more than just a few feeds from the utility provider plus a little tilt correction. I would consider cable too. I would probably look for copper braiding and center core. Will your cable be able to handle CONSTANT tidal swings without short term failure? All of these should be discussed with project supervisor. don't give to much info though. If they go with the other guy - let it be a disaster.