Or, alternatively, just play with three characters in the party. It is a slight struggle initially, but as long as the DM thinks of the party as one or two levels below actual level in terms of party power, it does work. Might be tough with a pirate ship to not have enough people to hoist the sails, unless the DM were to add in a few henchmen to the crew or tweaks the ship to remove such a need. (Come on: Magic anyone? Just saying... )