Yep, those would be my recommendations as well.
Broadsides by Living imagination is also out there, but I believe it is for gunpowder games. Ditto for Swashbuckling Adventures.
Me, I like gunpowder. Until gunpowder came about you generally didn't have any weapons on board for ship to ship combat.(As oppose to boarding actions.) Cannons take up a lot less deck space than even ballista, and using a high arc artillery piece like a catapult on anything less than a glass smooth sea is a nightmare to aim. As for trebuchet,,, a counterweighted warmachine on a pitching ship's deck... (shudder)
I believe Mongoose is updating their ship combat rules in the Book of the Sea, due out soon.
The Auld Grump