History of The British Canal System - Standard Locks

Standard Locks

For reasons of economy and the constraints of 18th century engineering technology, the early canals were built to a narrow width. The standard for the dimensions of narrow canal locks was set by Brindley with his first canal locks, those on the Trent and Mersey Canal in 1776. These locks were 72 feet 7 inches (22.1 m) long by 7 feet 6 inches (2.3 m) wide. The narrow width was perhaps set by the fact that he was only able to build Harecastle Tunnel to accommodate 7 feet (2.1 m) wide boats.

His next locks were wider. He built locks 72 feet 7 inches (22.1 m) long by 15 feet (4.6 m) wide when he extended the Bridgewater canal to Runcorn, where the canal's only locks lowered boats to the River Mersey.

The narrow locks on the Trent and Mersey limited the size of the boats (which came to be called narrowboats), and thus limited the quantity of the cargo they could carry to around thirty tonnes. This decision would in later years make the canal network economically uncompetitive for freight transport, and by the mid 20th century it was no longer possible to work a thirty tonne load economically.