For an alternate stealth agility game I recommend the Styx series.

For sailing and bashing heads I recommend Valheim.

For actual sailing and trading I recommend Sailwind.

For another singleplayer pirate experience I recommend Salt 2: Shores Of Gold.

Windrose also looks promising.

Blazing Sales looks like a blast of a PvP Battle Royale pirate game.

Blackwake is a free and straightforward pirate ship PvP game. Very fun but low server population numbers at odd hours.