This is a good start! Zapped Cow already pointed out a lot of the things I was gonna say, but here's some things I'd like to add:

• I like how there is an island with the same name as the game. Makes it feel important and gets you interested in it. Use this to your advantage!

• The UI is well done and you can access it bot via keyboard and mouse;
• The way things are far from each other gives a unique feel to the game. Maybe you can add something for the player to do when going to places that are far apart to keep engagement. Like something that happens on your ship while traveling;
• Making the map transparent could help looking at it while moving Diablo style. Or maybe make it smaller or even have a mini map on some corner of the screen. It's something you can experiment with;
• The thing I think you should work next is polishing the main mechanic of the game. Assuming it is combat, make the movement feel good, the cannons feel the most responsive possible, the enemies interesting (either via having good AI, enemies with different weapons, different behaviors, etc). Your game already has a lot of stuff (quests, items, a populated world), so your main mechanic has to be crisp to let you see the best way to fit all these components together.

Played your game for a while and liked it! Especially how ships from different factions are going from island to island. It gives some realism to the game.

It took my sometime to understand I need to go where there is the arrow and the white water to interact with the harbor. Also combat during combat I would have liked to see the enemy HP, maybe. So yeah it lacks a bit of feedback but overall a great game!