Looking for pirate-themed RPG PC game?

What I'm precisely looking for may not exist, but maybe I can find something close. It doesn't have to be a new game, as long as it plays on Windows 8.1. My computer is custom-built for gaming and can handle high-end graphics and RAM-demanding games. I would loveif I could find something through Steam; I searched but couldn't find it. I'm looking for a PC game that is RPG-style with pirates and/or high seas adventure. Elder Scrolls for the ocean would be close.

1. Open-world with as close to sandbox play as possible; I despise strict linear games where you go from Point A to Point B and that's it. Quests are fine, as long as the player can depart from the quest and go their own way when they feel like it, lol.

2. Single-player option. I don't have a lot of time to devote to playing and don't want other players waiting on me, or to deal with some of the world-class jerks I've encountered through MMORPGs.

3. Graphics don't have to be ultra-amazing, though I prefer not to have a cartoonish look. I don't mind Anime-style, especially Bishounen, but I don't like the blocky Minecraft look or Chibi.

4. I've had poor experience with early access games, but if there was something at the Beta stage, I would consider that as well.

5. I won't download illegally, so please no suggestions of torrent games, etc. :)

My favorite games are Oblivion, Skyrim, Fallout 3 and 4, Civilization V, Sims 3. I've played Sid Meier's Pirates, Pirate Cove, and Choice of Pirates already.