Semi-submersible heavy lift vessel Black Marlin is pictured, above, in Falmouth bay where she bunkered after a two month long voyage from China. 

The vessel was carrying the jack-up rig Prospector 5 which will be used in the North Sea.

Semi submersible vessels like the Black Marlin arrive on location take on water ballast and sink down to their operating draught. Then the cargo is either floated off or floated on leaving the vessel to de-ballast (discharge water ballast).