the revolving suspension heads on the posts it takes ten minutes to swing all the way through. In the double-pendulum block type, half of the cargo tackle can be anchored to the base of the boom. In order to double the hook speed, the halyard passes through the purchases since one end is secured which reduces the SWL to its half. Typical dimensions of a 275 tonne Stülcken are: 25.5 m length, 0.97 m diameter, 1.5 m to 3.4 m diameter of posts, 18 m apart the posts (upper end) and 8.4 m apart the posts (lower end). The hook of a full-loaded 275 tonne Stülcken can move 2.3 m per minute. If only one purchase is secured and the derrick is loaded with 137 tonnes the hook gains velocity to 4.6 m per min. Even more speed can be gained when the winch ratios are reduced to 100 tonnes (triple speed) and 68 tonnes (quadruple speed). Detaching the union table the double-pendulum block type of Stülcken is able to swing through which allows the lower blocks to swing freely to each side of the boom. In this way the derrick reaches a vertical position. A bullrope easily pulls the derrick to the other side until the weight of the cargo tips the derrick over. The span tackles now have the weight on the other side. The union table is fixed again and the derrick can start its work on the other side. There are also Stülcken with single-pendulum blocks. At this type the cargo hook is detached and the lower and upper cargo block are hauled into the center of the Stülcken. To tip the derrick over the gravity is here used again. A derrick helps pump oil in most offshore rigs. See also Crane Gyn Hoist Lighter Pumpjack Sheers References Further reading A swinging derrick white. External links Industrial equipment Lifting equipment