They're all slaved to the 8x18 curved hull so don't delete that one. The helm/wheel is also included. You can find them all under misc/misc.
You can follow this guide for building over water, but you might have to raise the foundation a few clicks before you start if you don't want waves clipping through the floor, then just place enough floor tiles to cover whichever size of hull you want to use.
The easiest way to place the hull that I found was putting it on one of these underground OMSPs, using the 'setquartertileplacement on' cheat, placing it over the first floor of the "ship," and shifting it around until it aligns with the floor tiles.
Now someone just needs to build MacGyver's houseboat. :D