A gyn is a form of three legged lifting device used on sailing ships. It provides more stability than a derrick or sheers, and requires no rigging for support. However, it can only be used for lifting things directly up and down. Gyns may also be used to support either end of a ropeway.
Two legs, called cheeks, are bound together as in the sheerlegs. The third spar is called the prypole and is fixed under the cheeks. Only four pulleys are required; three as splay tackles and the fourth one as lifting purchase. A timber hitch of six figure-of-eight turns and a finishing clove hitch lash the crutch but not too tight because the cheeks need some room to spread their heels. The cheeks of the gyn are now ready to spread and to be erected, the cheek splay tackle is hauled tight and then the other adjacent splay tackles can be lashed. At the sides, the gyn is unstable and it is crucial that the cargo is not swung out of the base triangle; consequently the gyn is only for lifting cargo vertically.
Gyns have also been used on land as part of the equipment to help assist water being pumped out of water wells in the Sinai Peninsula.
- Illustrations of a gyn and a gyn ropeway are on page 5-24 of the Sea Cadet Corps Seamanship Training Manual
- Ministry of Defence (Navy) (1995). Admiralty Manual of Seamanship. The Stationery Office. pp. 3–195–3–196. ISBN 0117726966.
- Graham Danton (1996). The Theory and Practice of Seamanship. Routledge. ISBN 0415153727.
- "3rd Light Horse Brigade War Diary". First World War Diaries AWM4, 10-3-15. Canberra: Australian War Memorial. 10–15 April 1916.