King of Seas has made it's way to GOG and Steam. The game will set you back $24.99US on either site. Take on the role of a pirate ship, do quests, gain skills, explore. So, if it's a pirate's life for you, this might be a game you've been looking for.

• Story: A series of quests guide you on your journey and uncover the intriguing characters of the King of Seas world who will lead you to the next path of your epic adventure.
• Procedural Generation: Dive into a lush, procedurally generated world that constantly refreshes the exploration mechanics within each new game.
• Dynamic World: The world reacts to your every action, naval routes change and with each conquered settlement the difficulty adapts to constantly give you a more challenging time.
• Map: A thick fog will ensure travelling towards objectives is not plain sailing, after all wouldn't you want to lose the joy of exploration !?
• Navigation system: Atmospheric effects influence gameplay. Sail during a storm at your own risk, escape the enemies and always remember to carefully watch the wind direction to stay in control during battles. The strategy starts here.
• Ship customization: Five types of highly customizable ships through an equipment and skill system, just as in any true role-playing game!
• Combat system: Not only cannon shots and nautical strategy but also speed and spectacle, thanks to a set of more than 20 skills to choose from and three branches of talents to suit any playstyle.

I really enjoyed Windward for a bit, which this game seems very similar to. Though it had cross platform multiplayer, and King of Seas is just single player.