Fun little game. I'd like a little more control in aiming and shooting. It reminds me a lot of Sid Meier's Pirates! But in that game, the ships were slower and the oceans were calmer, so it was less frustrating to aim. You also had multiple ammo types, one targeting crew, one targeting sails, and one targeting the hull. That would be a neat addition.
You should make the spyglass show a ship's hitpoints.