Would you consider releasing the code or doing a specific guide to the boat physics? Boat physics are something I have recently been interested in, but struggle to find a good implementation.
It doesn't seem like he's using any special boat physics here, lust a transform that he moves forward and rotates on the Y axis, then adds a small rotation on the Z axis to make it seem like it's turning into the curve.
If you're looking for some buoyance scripts, I could try searching through one of my older projects; I remember it being really difficult to find what I was looking for too haha