Just dumping some ideas here how stuff like bumpers, rudders would interact with the new shapes.

Boat Turning:
Since boat turning is now a thing via rudder, and i've seen some people complain about rotating while steering, an idea I've had was to make boats only turn when there's a rudder on it.
I got the code for that done already, if you need it. (May need some adjustments, though.)

Bumpers:
Bumpers are kinda wierd I'd imagine.
For custom shapes, maybe make the bumper protect a whole side. (as in, the area between 2 flags)? Not sure how the preset shapes would handle it though.