I picked up "Corsair" by Adament Entertainment just the other day. The book claims to be the best d20 guide to ships. It was written by the guys who brought us Skull and Bones which was published by Green Ronin.
My only problem with the game is a few historic concepts/ ship types (but then I read too much about pirates). I liked the ship to ship rules (movement might be a problem however) and found them better than other previous games. Check it out if you get the chance and let me know your opinions.
We've used a number of different sailing rules over the years, including Corsair. Its rules for ship movement are great for fast paced chase scenes if you are quick with the math and willing to wing it, especially if you want to run a scene with multiple ships near coastal features, for example in a narrow channel between two islands. The rules for ship to ship combat are not so great; they are most like a wargamer's rules, for times when you are more concerned with what happens to the ship then what happens to the people on the ship.
In the end, we've found that the Stormwrack style "cut to the boarding action" method is almost always best. Where Stormwrack really fails is in the chase scene, as it relies too much on skill ranks and randomness and doesn't leave much room for tactical decisions. It also really only works for two ships on the open sea. If you want more than two ships involved or to include coastal terrain, then Stormwrack is inadequate. So what we're trying now (or in a month or so when we get to SWW), is to use the Corsair rules for chases over long distances and then cut to the Stormwrack rules when it gets neck and neck.
But then, my current players are neither wargamers nor sailing enthusiasts, so accuracy sometimes takes a back seat to pacing and story. For large scale ship to ship interaction, Corsair is one of the best out there. Highly recommended. Also makes you want to get your hands on some 1:1200 miniatures.