Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A caisson lock is a type of canal lock in which a narrowboat is enclosed in a sealed box and raised or lowered between two water levels. It was first demonstrated at Oakengates on the now lost Shropshire Canal in 1792, where its inventor, Robert Weldon (b:?1754 to d:1810) built a half-scale model. He patented his invention as the ‘Hydrostatick Caisson Lock’. The full-sized box would probably have displaced about 270 tonnes and weighed about 170 tonnes, including the water in it, so about 100 tonnes of ballast would have been needed to give neutral buoyancy. The box would have needed to be strong enough to withstand the pressure of 50 feet (15 m) of water i.e. about 3,000 lbf/ft (150 kPa) gauge pressure at the bottom of the chamber.

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