... Okay, not a pirate ship per se, but any tileset depicting an 18th century English Tall Ship would be nice. It would also be great if it were at least somewhat similar in style to Inquisitor's XP Outdoor tileset (http://www.rpg-palace.com/downloads/details.php?id=102). I'm sure one is floating around somewhere.
Also, if you happen to have one lying around, please make sure that it comes with all of the typical shippish features, such as sails, masts, etc., otherwise it wouldn't be an 18th century English tall ship.
Live long and prosper.