RULES:
I suggest making your maneuverability rule based on how many squares you have to move to make one directional change (so from West to Southwest or Northwest for example) rather than completely u-turning. Your rule technically works, but it seems strange to be able to flop all the way around or just turn a little in the same span.
Maneuvering in tight quarters (shoals, etc) would be very difficult with your turning system. I suggest allowing one facing change per round if movement is 1 square or less.
Wind filling sails should be based on whether the wind direction is Good, Fair, or Poor for that ship's rigging. A square-rigged ship should be Good if the wind is behind or to either flank, Fair if from either side, Poor if from ahead sides, no movement if straight ahead (in irons). A Fore-and-Aft rigged ship should be Fair everywhere except from straight ahead which is no movement.
Movement should be calculated based on the ship's speed at the start of the turn, regardless of turns, which means a fast ship can jibe right around through the irons and onto the other side without losing power next round. Or, if conditions or planning are bad, the ship could be locked in irons for a round and get out of it next round in one of the adjacent directions.
Include a rule for water flows, for example if you have a big river or fjord with an incoming / outgoing tide or a sea monster whirlpool. Simply, give every ship in the area extra movement in the direction of the water flow regardless of size or speed. Makes going upriver a challenge unless the wind is with you.
With boarding, you let the player roll for every 10 men instead of individually. Great! Do the same for cannons: roll in groups of 10 until you hit a remainder, which you roll once more for. So a ship with 38 cannons (19 per side) rolls two attacks when firing to starboard. The first attack is 10 cannon, the second is 9. If you also fire port, roll twice again, 10 and 9 cannons.
Reloading time for cannons?
No rules for oars?
What about small boats?
Visibility ranges / distance of encounter in various weather and time of day.
Weather generation rules? Remember you need to write everything for other people to be able to run your game.
Recruiting men?
Adventures: Search for buried pirate booty, search for lost city, search for sunken wreck, grab the silver train!, grab the treasure fleet!, assassinate governor, disrupt shipping, raid plantation / mine, arrest outlaw, protect a town, negotiate with indians, help a monastery / mission, indian attack on town, plague in town, gold mine near town, pirate attack on town, town collapses from undermining (as Paint Your Wagon).