Well, with it's lack of walls, it really resembles Fort Raleigh, (Roanoke Island, NC, USA). Which is basically a tall, fort-shaped earthen embankment surrounded by a ditch. ;-)
8-o AMAZING! Simply amazing! If only I had that many (coordinated) bricks to build with, I'd build something that large too... But it'd probably be the "free-port" of Tortuga. More pirates that way (more rum therefore). I have very few Imperial (insert faction here) mini-figs... But honestly, Nice work! *y*
But is that ALL you've got? I'd just have a couple guys swim over and dissable their rudders. And maybe shoot a couple rounds of hot-shot at them while their still trying to get in position. Maybe even stinkpots.