Addressing all the posts about lack of adventuring hooks/locations:I'm planning on this campaign to be a more roleplay-heavy one. There are many campaigns that take place primarily in one city, where political intrigue is the driving force. As for dungeons: maybe scouts reported that one of the ships fell behind last night and hasn't moved since. The PC's are now part of a search party to go back and figure out what happened to this ship, only to find out that it's been taken over by a rebel group of ____ for ____ purposes.
The ammunition issue is a significant one, and one I hadn't thought of. I will definitely like to figure out a solution to how to forge things on a ship, and where to get the materials.
Technically speaking, ANY urban adventure/quest can work with a series of ships. An uprising sect? A rigged election? An arcane experiment gone haywire? A theft? There's a ship for it...
Dungeon crawling can be reserved to underwater scavenging hunts, exploring sunken cities and ships and fighting aquatic monsters.
Transport between ships can be done with Teleportation Circles.
My 2 cents on the subject