I've noticed this 'bug' the last few days. If I'm using the boat then there's no damage, but as soon as I leave there is an intermittent 10 damage and crashing sound, even though it's not near any rocks, and in deep enough water. The sea/waves seem to make it rise and crash down taking 10 damage every few seconds, even though the sea is calm. Admittedly I had traveled through a storm, and it's almost as if the boat still thinks it's in a storm by it's behavior.