This was cool, I did a pirate ship/crew themed game as well!
One bug I found was that my upgrades reset between runs on my ship, but the base still thought I had purchased them.
I'd recommend enemy ships don't engage with you until you come near or raid an island, just to make it more of a risk-based engagement and not a constant onslaught.
Great work, the game loop feels complete and the controls are tight!