Once the mission begins you will find yourself in a steamboat which is being over run by some renegades. Your objective is simply to repel them and survive, along with ensuring Neds survival, though he can really look after himself on easier difficulties. Once you unblock the water paddle at the back of the boat, Ned will tell you to go onto the cannon, this part is relatively simple, just shoot the incoming boats and hit the fort, it can take a while to get used to the aiming of the cannon but after a few shots you should get the hang of it. Once the steamboat has run aground, you will need to reach the top deck and meet up with Ned, once there; the attackers will climb over the sides of the boat, and will run down the walkways. Just fend them off until an achievement appears, signalling the end of the level.