Time ago I had this idea, and as 3 or four years later (with a fifth time of tried to make the Going Merry Ship) here is, sadly unplayable for now.
I was afraid for the size of the 3D model, but the game runs without problems or lag and just added 7 Mb.
I need to find a way for make some colliders (.col), tried with GTA tools but won't works, I will try with Unity (I guess I'll have the same results, but lost nothing for try)
Told you One Piece fans, I have sometime special for you ;]
NOTE: The ship is visible on the beach only, not playable for now.
Install it with Illusion Wizard