Locks, bridges and tunnels


Turning a lock is a daunting task for beginning narrowboaters for several reasons: it is the one canal task that can cause serious damage or injury; despite being a fundamentally simple technology, it can be difficult to understand how it works; and most significantly, it exposes a beginner to ridicule. Unless you have enormous self-confidence, you will approach your first lock fearing the laughter of children and the scorn of your fellow boaters.

note iconPeople who watch canal activity are called gongoozlers (especially if they offer useless advice). Gongoozling is similar to trainspotting (what railroad train watching is called in the UK).

One way to avoid looking stupid is to watch other boaters turn a lock and see how it’s done beforehand. Perhaps you can schedule your vacation so that you can spend a day on the canal before you book the boat. Most people on the canals are happy to talk and offer advice to beginners, as long as you don’t get in the way.

Three-quarter angle diagram (with uphill gate closest) showing the major components of a closed narrow lock: water in the pound, uphill sluices and gear crank, lower gates with gate paddles and beam mounted crank
Diagram of a narrow lock with uphill ground sluices and downhill gate paddles

How a lock works

Because it’s a pretty simple technology, canal locks haven’t changed much in hundreds of years. A lock on the Panama Canal works on much the same principles as a lock on the Leceister Canal. Both canals employ pound locks, meaning that a short body of water (the pound) is contained between two locks (the gates). Technically the gates are the locks, but most people collectively refer to the two gates and the pound as the lock.

For such a simple technology, however, there is quite a variety of locks on the canals. There are single-boat locks, double-width locks and the massive locks on the Thames. Boaters turn most locks themselves, manually turning a windlass to raise paddles, but some are overseen by lock keepers, some are operated by lock keepers and some are operated by electrical motors controlled by boaters or lockkeepers. There are flights of locks, staircase locks, guillotine locks and even diamond locks (but precious few of those).

Water is generally allowed into the lock (on the uphill or higher side) via sluices that are built into the banks of the lock. Water is generally let out of the lock (on the downhill side) via openings in the gates or by sluices built into the bank, just as on the uphill side. In either case, the openings in the gates or the sluices are controlled by paddles. (In actual practice, you’ll see many combinations of gate and ground paddles.)

Diagram showing the parts of a ground paddle crank, including the ratchet and pawl mechanism that keeps the ground paddle from dropping
Detail of a ground paddle crank showing ratchet and pawl

The paddle is connected to a metal rod which in turn is connected to a metal-toothed bar or rack. The rack (and the paddle) is pulled up or down by the pinion, which is a round, toothed gear that meshes with the teeth on the rack. The pinion is turned by a windlass crank (also called a lock key), which is inserted over a spindle or shaft.