Operating Locks on British Canals

The Procedures for Taking a Narrowboat Up or Down a Lock

Nov 13, 2009

Here is an outline of how a lock works and how to operate it safely and efficiently

Operating a lock is a simple process, but it needs to be understood so that boats can make their way through with reasonable speed and thus not inconvenience other canal users.

Operating the Gates of a Canal Lock

The gates are of two types, upstream and downstream. In narrow locks, where there is room for only one standard narrowboat, the upstream gate is single, being opened and closed by pushing a balance beam on one side of the lock.

The downstream gates are double, meeting at an angle that points upstream. This is so that the weight of water in the lock forces them shut. However, each gate has its own balance beam, one on either side of the lock, so the operator of the lock must use the walkway on top of the gate in order to open and close the other gate. Braver souls step across the gap between the open and closed lower gates, and more cautious ones walk all the way round!

In broad locks, the upstream gates are also double. If a single narrowboat is using the lock it is possible to proceed by only using the gates on one side. (It is also possible to only use the paddles on one side, but the water will enter and leave the lock more slowly).

The gates can only be moved when the water level is the same on either side. Experienced lock users have a good eye for judging this, and a sense of when the gate will open and when it will not. Even so, quite a bit of effort is needed to push the balance beam, and most people find that putting their back against it and using leg power is the best way.

Operating the Paddles to Raise and Lower the Water in the Lock

The paddles control the flow of water in and out of the lock. There are two types, gate paddles and ground paddles, which refers to the location of the mechanism that opens and closes.

The paddles are opened and closed by using a windlass (a right-angled metal handle) on a spindle. There are generally two square holes at the end of the windlass to fit the different spindles that are encountered on the British waterway system.

The spindle operates either a rack and pinion mechanism or a hydraulic system. In both cases a safety catch ensures that the paddle stays in place when it is raised, and it is important that the safety catch is used properly.

Spindles for gate paddles are on the gate itself, whereas those for ground paddles are on pillars next to the gates.

The golden rule when lowering a paddle is to do so by winding it down with the windlass, not just release the safety catch and let it drop. This could damage the mechanism.

Another golden rule is never to let water into a lock unless the downstream gates and paddles are closed. If they open, the lock will never fill! Also, before leaving the lock, make sure that all paddles and gates are closed.

The Chamber of the Lock

It is possible to operate a lock single-handedly, but much easier if somebody stays on the boat at all times. For one thing, the boat will move about in the lock as the water flows in, the tendency being to throw the boat forward due to the motion of the water flowing underneath the boat and then back over the top. A boat could damage the gates by hitting them too hard.

A crew member can help to keep the boat in the right position in the lock by standing on the edge and holding the boat with the centre rope. It is not a good idea to tie the boat up when in the lock, because of the rapid descent of the boat as the water empties.

When filling the lock, do so at a speed that is comfortable for the person controlling the boat. They may want the water to be let in slowly at first but then to speed up.

There is a lot to think about when operating a lock, but it all becomes second nature after a while. It is important to bear in mind that locks are dangerous places, and also that other canal users should be inconvenienced as little as possible.

The copyright of the article Operating Locks on British Canals in Boat Safety & Maintenance is owned by John Welford. Permission to republish Operating Locks on British Canals in print or online must be granted by the author in writing.