Drilling imminent., page-2

Yes the rig is at the drilling site. For those wanting something to read while they wait, here is a little something about the next step: the tricky lowering of the legs: For the independent-leg units, “preloading” is required to drive the legs into the ocean bottom before the hull is completely jacked out of the water. During this procedure, the jackup MODU is at risk from weather and leg “punch through”; i.e., one leg breaks through a hard crust, putting the other legs in a large bending movement. Generally, 5-ft swells and/or a combined sea of 8 ft are the maximum seas in which these units can jack out of the water. If the hull should roll, pitch, and heave to an extent that the legs come into contact with the ocean bottom, particularly if it is hard, the legs can be severely damaged. The preload sequence is usually done in stages, with the hull never rising more than 5 ft out of the water to safeguard against having a leg punch through. If the ocean bottom is soft and consists of clay, it is not uncommon to take 7 or more sequences, with each sequence taking 7 to 12 hours. The unit’s pumps seawater into its preload tanks, adding weight to the hull and driving the legs. After the legs are driven and the hull goes into the water, the seawater is dumped overboard and the sequence is begun again. This process occurs until the legs no longer penetrate the ocean bottom. The concept is to load the legs to a level above that which the unit will encounter in the harshest predicted environment. The newer, enhanced premium units do a single preload in which the jacking system is strong enough to jack the unit with all the preload water onboard, the basic weight of the hull, and the full transit VDL. This is a significant advantage in that a much smaller “weather window” can be acceptable to move the unit. Jackups are most susceptible to major damage or loss when they are floating.