I would recommend just splitting the food and liquor 5 ways just like the boat. Liquor is dirt cheap so the cost should even out.
For ice, water, mooring, dock, tips, fuel, etc I would use a boat kitty. Have everyone chip in $100 on the first day and put it someplace accessible to everyone so they can grab it as necessary. Or you can designate a purser who uses the kitty to pay for everything. If the kitty depletes, everyone throw in another $50 or $100. On the last day, spend the rest of the kitty at the bar...
.
