@Dustin: Every ship has AP, it is maximum when the ship is undamaged and you lose AP whenever the sail or the crew is hit. If your AP is less than 15, you are unable to attack. It works for your ships and for the opponents as well.
I just did a video playing level 24 (last level) with no trial and error for those who doubt it is possible: http://youtu.be/hE_1zcdqjig . It is a bit long though, I took my time to think, didn't have it memorized.
All 24 puzzles can be done without trial and error, just by logic. Vote that up so people stop complaining stage 24 is impossible without "cheating", it is possible.
Great TD, one of the best I've ever played. The only thing that I think could make it better is if we could choose who to help, getting to different endings.
I think the auto combat was a big step back. Option to turn auto on or off on the previous game was great, this one makes you try to use magic as a Warrior, melee as a Mage with full mana, etc. At least including a button in battle to choose from "Melee", "Magic" or "Mixed" would be great.