Tech porn for those who like it...and you better start making that ultimate cop of coffee.A jackup is a floating barge fitted with long support legs that canbe raised or lowered. The jackup is maneuvered (self-propelled or bytowing) into location with its legs up and the hull floating on thewater. Upon arrival at the work location, the legs are jacked down ontothe seafloor. Then "preloading" takes place, where the weight of thebarge and additional ballast water are used to drive the legs securelyinto the seabottom so they will not penetrate further while operationsare carried out. After preloading, the jacking system is used to raisethe entire barge above the water to a predetermined height or "air gap",so that wave, tidal and current loading acts only on the relativelyslender legs and not on the barge hull.Modern jacking systems use a en.wikipedia.org/wiki/Rack_and_pinion gear arrangementhttp://en.wikipedia.org/wiki/Jackup_rig#cite_note-2 where the pinion gears are driven by hydraulic or electric motors and the rack is affixed to the legs.Jackup rigs can only be placed in relatively shallow waters,generally less than 400 feet (120 m) of water. However, a specializedclass of jackup rigs known as premium or ultra-premium jackups are knownto have operational capability in water depths ranging from 500 to 625feet