Fairbairn steam crane

A Fairbairn crane is a type of crane of an 'improved design', patented in 1850 by Sir William Fairbairn. There are numerous hand-powered versions around the world and one surviving steam-powered example in Bristol Docks, England.

The crane's innovation was in the use of a curved jib, made of riveted wrought iron platework to form a square-section box girder. This curved jib could reach further into the hold of a ship, clear of the deep gunwales alongside the quay.

Designing a strong curved jib required Fairbairn's advanced theoretical understanding of the mechanics of a box girder. The tension forces were carried by the outer, convex surface of the girder which was made of back plates being chain-riveted together. The inner surface carried a compressive load. To avoid plate crumpling, it was made as a cellular structure: an inner plate and webs formed three rectangular cells, effectively box girders in their own right. The character of a box girder is to resist torsional twisting, so a composite face built up of them is also good at resisting crumpling.

The first of these cranes were a batch of six built for the Admiralty at Keyham and Devonport. These were hand-operated and could lift 12 tons to a height of 30 feet (9.1 m) and a radius of 32 feet (9.8 m) . The size of the crane jibs was determined by ships of the period, and their lifting capacity by men's ability to raise the load. Experiments at Keyham with loads of up to 20 tons showed the jib design to be sound, and that the jib at least was capable of handling loads of up to 60 tons.

A "colossal" crane of 60 tons was later built at Keyham, with a cell plate stiffened by four cells. This crane was worked by four men driving through a gear train of 632 times, which must have been hard and slow work at full capacity. As the capacity of the crane was so obviously limited by its motive power, not its strength, they were an obvious candidate for steam power – as was later re-applied to the 60 ton crane at Keysham. There was even a proposal for a 120 feet (36.6 m) high crane, to replace masting sheers at Woolwich. A more typical size for most of these later cranes though would be able to lift 35 tons at a radius of 35 feet (10.7 m). They were powered by self-contained steam engines, with both boiler and engine mounted on board the crane.

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