I was experimenting with buoyancy, but now Roblox added theirs, and theirs is mostly better, so...
By the way, this boat sinks in a different way every time (regens after sinking or a set amount of time), including failing to do so, occasionally. It uses a script that actually simulates the movement of water from an initial hull breach through each of the rooms, with some of the doors open and some closed. It then simulates buoyancy (via script, pre-water) to animate the sinking.
Also, yes, this place does use a free model. I didn't want to waste my time building a boat for an I experiment I wasn't sure would work. That is the RIGHT reason for using free models.
Allowed Gear types