so I was thinking you could add some natural things that happen at sea to hamper your progress in combat maybe,

large freak waves would need you to sail into them, side on and your toast, whirlpools would need to be avoided or you get sucked down.?

Moby dick charging through the water trying to ram your boat.?

also it would be nice to have different times of day and night to spice things up a little.?

different types of ammo for different types of boat/ship, you could order your men to change ammo maybe, which would add possible tension as this would have to take a small amount of time say leaving you more vulnerable ?

oh ive got loads of ideas and i'm only tipping the iceberg! OMG there you go ive done it again, another hazard, remember the titanic.....?

right I gotta go, before I design a game :)