Someone said something the other day, can't remember exactly what, but it carried with it the question "what rams drop as loot from sailing?"
The most interesting I've seen, so far, was the Steel ram. This is the one only drops at wave 32 of Cannon Defense.
I've seen the Priming ram drop three times. It's weird--I some really good mariner pirates in our guild are still waiting for it.
Others:
Fiery
Gunner's
Hasty
(more will be added to the list as I confirm them.)