Also known as “pin and hole”, the system consists of a series of holes that are drilled into the legs and a set of pins that are inserted into these holes. The pins lock the legs in place and hold it. When the rig needs to be moved, the pins are moved and the legs are lowered to the seabed.
The hull is elevated or lowered by large hydraulic cylinders. When, at the end of the stroke, the leg is locked off with pins, then the cylinder is reset and makes another stroke. In elevated condition, the platform is normally supported by the pins.
The pin and hole system has been used in jackups for many years, due to its simplicity and reliability. However, it does have some limitations. The system only allows for hull positioning at discrete leg positions, which can limit the flexibility of the rig. They can’t provide a continuous jacking operation and jacking speeds are relatively slow.
