Originally posted by wizard_of_woz:

Ok a lot of you are treating the OP like they are dumb. There is a known bug where your boat takes random damage while sailing. I have had it only happen once, but seen plenty of people talk about it. Seems to be more common on multiplayer vs single player.

When the sea is strong and the waves are high and you are sailing under full sail, the boat will jump through the waves, of course it will be damaged. But you will see your boat change color so you know it has been damaged. You can sail ashore, build workbench and repair the boat.