The twin-7000t Micoperi revolving floating cranes have total 15000t joint capacity at 45m outreach.  This is the world largest floating crane.  The picture above shows the cranes starting to set two-5,400 ton segments of an oil platform (10,800 tons total).  

Rich Phillips designed this truss boom structure of the giant twin-7000t floating crane during a previous engagement. The boom length from the hinge to the main falls is 100m and the jib is another 45m.  The auxiliary hook can work under water to depth of 500m.