Age of Booty

On mission 6 of 7 ("Skirts and Fins") in the medium campaign, the merchant ships only have bombs. You can take a town, park beside it and keep darting out to take out merchant ships.

When you get a bomb, scan the map for towns already under attack by multiple enemies, and drop the bomb beside them. The other two team's ships are very aggressive, and will often attack the same time at once. The boats don't have to be from the same pirate team.

This is very easy to get all you need to do is destory two boats with one bomb the boast have to be pirate ships and not merchants. I found that the best way to get this achievement is to make a split screen game and change the curses to bombs only then change the merchants to 1 on the slider. Now just sing in two more players and start the game, the first your going to want ot do is obtain a bomb by killing a merchant and waiting for the bomb crate to float to the top of sea.

Once you have that you will want to get the other two boats to some where you want start firing at them to lower there health to about a quarter just to make sure. Now just move back a hexagon and drop the bomb.

Me and my friend boosted this online. We started up by hosting a 2v2 match, and set all the curses to bomb curses. Have both players add a second controller. Have your friend move both enemy boats away from the base and get them to attack a town till they're on low health, then with a bomb you collected from a merchant get your mate to put the boats together then stick your bomb in a place where it will affect them both. Press Y. Then BOOOOOOM! Achievement unlocked!

Oh, and racing wheels count as a second controller, as that's what my friend used.

Or you could do it like this video, making a really small custom map with loads of enemies and the merchants only having bombs. Credit to RoosterTeeth for the video.