Jack-up rigs are generally used in more shallow waters where deep water drilling is not required. Since they are movable, they are frequently utilized by drilling companies to assess the viability of a location before a more permanent solution is implemented.
A jack-up rig consists of a hull supported by 3 legs below. The drilling set up is located on top of the hull. The three legs pass from underneath the hull to the top and are jacked up when necessary using a set of motors. When the rig is in place, the legs are lowered until they reach the seabed. The hull is then jacked up along the legs until it is about 60 to 70 feet above the water. At this point efforts are made to stabilize the rig by allowing water into the preload tanks. After a day or two, when the technicians are sure the rig is stable, work begins. To move a jack-up rig, first the hull is lowered until it floats on the water. Then the legs are raised using the motors. The legs are designed to pass through the hull up into the air, achieving a substantial height. Tugs are attached the hull and it is towed to wherever it needs to go.
A Jack-up rig is relatively smaller than the other vessels and explained earlier is generally used for temporary set-ups or where deep water drilling is not necessary.