There's an overwhelming number of cars and other land vehicles, and planes and other sky vehicles, but only a scarce few watercraft. There is only one by default, and the only boats I can find are old and/or don't work. I feel as though water is half useless without something to drive through it, the most you can do is row or swim between islands in a tropical sort of build.
A good place to start and look for inspiration would be GTA's boats.
Also slightly off-topic. GSF's aircraft carrier came with a no-mount script. I'm wondering if there is, or if it's possible to make, a standalone version. This could lead to larger vehicles where the passengers do not need to sit being made, though I recall this concept being very buggy, so...
