How this works:
Firstly you need Island Paradise. Then you need a port. In this port you need to create a 20x6 barge. You then use the game cheat moveobjects on and place the fishing trawler over the barge. You should see a edge extruding the ship's floor. It extrudes only slightly. The back of the ship should cover up the staircase in the barge. You can hide the dustbin and the mailbox inside the ship. The helm should be placed behind the main mast as shown in the last picture. The Sim's feet hide a slight bit below the ship's floor. If I had uncovered the Sim's feet completely, the edges of the barge would extrude far too high above the ship floor and would look rather ugly. The extruding edges of the barge fit nicely on to the rear section of the trawler.
If you don't know how to build a port or a barge please go to the EA site, there are plenty posts there to help you.
Fishing trawler Anabela - sailable