Looks like you have some collision shapes that are scaled (which Godot warns against doing) and also your hull mesh is scaled (it's not allowed for the same reasons that Godot doesn't want you to scale collision shapes, but this probably isn't in my documentation). The end result is that Hydro thinks your boat is a 1x1x1 cube and it spins accordingly.
When I resize the collision shapes and mesh and revert the scale to 1 for everything, it starts acting like a boat. Once the shapes were working I had to bump up the mass as well.
I do want to make Hydro more ergonomic to use in the next version, so I'll make note of the scaling issue. If I can't make it deal with scaled objects automatically, in the worst case I could at least trigger the warning icon to show up when a shape is scaled.