If you are swimming in the boat and you are wearing boots, if you would look underneath the boat, you will see boots penetrating the boat's hull.
How to reproduce:
Wear boots, get in the boat, switch view with F5, look underneath the boat, see boots penetrating the boat.
Take off boots, look underneath the boat, boots/feet do not stick through

What I'd expect to see:
I would expect to NOT see the boots penetrate the boat.