A better way to destroy your boat is to make sure you have the inventory space, then stand next to the mast and hack away at it. When the ship breaks everything goes immediately into your inventory, even if in deep water. The items "spawn" at the center of the ship.

Kudos to Jiroc when I came across this gem. (Was looking for what to do during a capsize event in a storm, but I don't think this would help when the boat's literally upside down:)
https://www.youtube.com/watch?v=p6G19m-gFKg&ab_channel=JiroctheViking