The hoists run on a 18m (60ft) monorail mounted on the underside of the platform. They lift special heavy drill-hole caps called blow-out preventers about 10m down to a platform floating on the water.
The hoists are unusual because they run on hydraulic fluid rather than air pressure. “The major competition out there are all pneumatic,” said technical sales manager Steve Hanna.
He said the main benefit of a hydraulic system is that it can lower a load in an emergency in a controlled manner. “You can’t have an emergency lowering operation on pneumatic power,” he said. “To do it you need a separate air supply.” In contrast, the hydraulic system can bleed off oil through a relief valve to lower a load.
Operators control the hoists with a control panel mounted on the deck of the jack-up. A valve block in the panel controls the flow of hydraulic oil under a pressure of 200 bar (3,000 psi). The hoists have a flow rate of 1.5 litres per second (23.75 gallons per minute). An electronic load cell cuts off the fluid at 105% of capacity.
MOS designed the hoists to be built in Singapore by Regional Marine. It expects the first set of two to be delivered to jack-up builder Keppel Fels in September, and the second set of two to arrive in the middle part of next year. Keppel Fels is building the rigs for Ensco International, a Dallas, Texas-based drilling contractor.
It is the fourth set of hoists that it has supplied since designing the first lot about two years ago.
