Guide: http://www.gamerguides.com/assassins-creed-iv-black-flag/
iPad App: https://itunes.apple.com/us/app/gamer-guides/id599410871

The El Impoluto is an ominous sight and can be a massively tricky encounter your first time around. This vessel's two major strengths are its ram which can cause devastating amounts of damage even on a fully upgraded hull and its broadside attack which fires more cannons at once than you can count. As most of its firepower lays in the front and sides of the vessel, the obvious safe spot is in the water behind it.

Unfortunately the El Impoluto is quite a maneuverable ship and can change its direction and pick up speed extremely quickly. If you see the ship sail right out of your range of attacks and then turn suddenly you know that it is about to ram at you with speed. If you do see it coming, do not try to steer to either side of it -- this invites the El Impoluto to slam directly into the side of your vessel, which is pretty much an instant de-synchronisation.

Instead; try to turn all the way around and off to the side, so that your back is facing it. This will cause a glancing blow rather than a deadly one and you can hit it with a heavy shot or two as it comes up your side. Due to its speed it will also end up in front of you.

This is where you should attempt to spend most of the fight. From here you should still be able to use most of your attacks but don't get carried away as the major focus of your offensive efforts should be on dropping mortars and using the chain shot. Every time it attempts to ram you, repeat the process and then stick to its rear as long as you can.

Eventually, with a bit of luck, and a lot of practice you will be able to fell this monster.