Nice concept i dig being a pirate in a management game. It would be nice to have more dynamics like things that would make me feel more in control of a ship rather than a cursor, like ocean currents that make slow you down or make you faster.
Another thing i think would benefit the game is that ships should try to avoid you, also you could add a collision system for the ships so you can even add a damage meter that require gold for repairs.
I hope you find the feedback useful.