With this exploit you can easily do I'm on a Boat Achievment.
Theres a spot on enemy boat (for Horde - don't know 'bout ally though) where boss cannot reach you. The group that is going to kill mage jumps on the enemy's boat, kill him, then using your rocket packs you all should jump up to spot shown on the picture below, and simply wait for next mage to spawn. Repeat until you're done. Remember to jump back to your own ship when enemy's ship is going to be destroyed - if you will remain there you won't get achievment.
Short version:
1. Attack team jump on other boat to kill mage.
2. Instead of jumping back they jump into specific spot in front of boat.
3. When mage is back, jump down, kill him.
4. Repeat until enemy boat is going to go down.
5. Jump back on your boat.
6. PROFIT!
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