There were a couple bugs in the system; for some reason the enemy pirates/sharks seemed to delete themselves before ever reaching the convoy. Turn rate should definitely be increased somewhat to make it feel more responsive, especially before attatching any ships.
I agree with one of the previous commenters that the ship-chaining thing is very interesting, and I think that it should be a core game design tenet; something like, the more ships you chain together you get a higher score or something. As of now, it's way easier to take in one ship at a time.
It would be good if there was something more than just trying to get those 5 star reviews. I think that if this were expanded, a decent direction to go would be to include a business-type aspect to the game: get money to expand/upgrade your boat over time.
I think it's an interesting idea, definitely. The art is fairly cohesive, and the music is fine - but short and could use a few more bars. Good work!