oobject.com brings us this story on 10 of the world largest floating cranes.
10 enormous floating cranes
Aside from their spectacular size, what makes floating cranes unusual and interesting objects is that they are essentially boats. As such, they don’t exactly conjure up the idea of stability, which is the primary requirement for lifting things. They also look weird since boats usually consist of large hulls with smaller superstructure, here the arrangement is reversed making them seem very ungainly. Some of these cranes can lift tens of thousands of tons, at sea, and are engineering wonders.