by landing on a boat while crouching it looks like you are not crouching, boats can be used to see through blocks, boats can clip you through the ground

on every version with new boats getting out of them while on slabs/layered snow while there is a block above you moves you into the ground and while you can't normally crouch on a boat, if you jump, crouch and then land on the boat you will crouch on it while your player model shows you standing. the hitbox is the crouched hitbox though. this could be used on server to find bases and even get in bases while you can't normally get in but by using the boat to go through the ground.