Derricks or Cranes are used on general-cargo ships to lift the cargo on and off. They are usually capable of lifting between five and ten tons but the ship may be fitted with one or more heavy-lift derricks i.e. Jumbo Derricks to cope with the heavier items of cargo. Derricks are usually used in pairs. One is fixed over the hold and the other over the quay. The two runners are then joined together and the cargo lifted out of the hold by the ship derrick. It is moved over the ship’s rail by slacking on the ship derrick and heaving on the over-side derrick. The over-side derrick then lowers the cargo onto the quay. This is known as the ‘union purchase’ method. This has the advantage of rugged simplicity and universal acceptance by stevedores. The shipboard crane is initially more expensive but it requires fewer stevedores. It can pick up and put down the cargo over a much wider area (it has better ‘spotting’ facilities) and it is quicker. The ship’s lifting gear is subject to Merchant Shipping Notice No M1347 concerning safety and it must be clearly marked with its SWL (safe working load).