Canals & Waterways

Locks: Uphill and downhill on a boat

Locks - How They Work

Sketches courtesy of Tel Monks. Dave [email protected] has converted them into a nice animation (68K). I suggest you take a look at the animation, then come back and read this page. [Please note that the sketches and animation are incorrect in one respect. In a real lock, the gates open the other way, toward the high water side.]

Boat descending a lock.

Referring to the picture and sketches, visualize two bodies of water, one whose surface is, say, 8 feet above the other. Visualize a "tank" (the lock) between the two bodies of water. The tank extends a few feet above the higher water surface. Now suppose we are cruising along in our boat on the upper body of water. Suppose also that the water level in the tank is at the same level as we are. Then there is no problem in opening the door (gate) on our side of the tank, and driving ourselves in. Boat approaching a lock.

We close the door behind us. We are now floating in the closed tank. Now what? Well, using an interesting contrivance (a "paddle"), one of our crew starts to let water flow out of the tank into the lower body of water, sort of like emptying a bathtub. As the water level in the tank goes down, our boat naturally descends with it. Boat in a lock.

When the tank is finally drained to the same level as the lower body of water, we can open the door on that side (another "gate"), and steer our boat out. Boat exiting a lock.

For going up, we steer our boat into the drained lock, close the gate, allow water from the upper body of water to flow in. When the levels match, we open the upper gate and drive out.

Now that you've gone through the explanation, you can try to do it yourself using an interactive lock animation, by James Pascoe. Just replace his word "door" with "gate", and his word "sluice" with "paddle". As long as you have not disabled Java on your browser, you should be able to use the animation. (Note that this animation has the same problem as the previous animation and sketches - the gates open in the wrong direction-- but the basic principles are still intact.)

A relative rarity on the canals is a set of "staircase locks." The upper gate of one lock is the lower gate of another. A lock is filled using water from the lock immediately above it; or, from the other point of view, a lock is drained into the lock immediately below it. These locks are ordinarily manned by lock-keepers, since everyone else gets hopelessly confused. You can see if you get totally confused too, by trying the staircase lock interactive animation, from This one should work for you provided you have not disabled Javascript on your browser. (For this one, the labelling is even more confusing for those used to UK canals: once again, the lock gates are called "doors", but this time the paddles are called "gates"!) Once you're flummoxed by the staircase locks, the same site also has a single lock simulation available.

Another relative rarity on the canals are "side ponds" associated with locks. The side ponds allow a full lock cycle (from full to empty to full again) to be done WITHOUT using a whole lockfull of water. This seven minute video on Using Lock Side Ponds New! shows how this works.

[Photo: believe to be the second lock from the bottom of the Atherstone flight on the Coventry Canal.]

Read about how Joan and Pete Payzant first learned how to operate a lock.

Nigel Bromley has a detailed page on Canal Locks - collected thoughts on their theory

Very thorough coverage of locks, in all their variations, may be found on the Wikipedia page Lock (water transport).

Locks - Who Does the Work?

On the U.K. canal systems, your crew will operate the locks yourselves, perhaps with the help of crews from other boats. It can be a nice social occasion. You'll need to drop one or two crew members on shore prior to each lock, and pick them up again after passing through. On river navigations in the U.K. (e.g. the Thames), and on many European canals, the locks are operated by lock keepers.

Lockkeepers in France only require a very small tip for their services. They are well known to offer items for sale: home-made goat's cheese, eggs, fruit, and vegetables.

For another way to get boats up and down hill, see lifts.

For an example of lock repair, see Photographs of Stenson Lock's bottom gates being replaced

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Text and photos Copyright © 1995-2012 by George Pearson.
Page Last Modified: Saturday, 17-Oct-15 5:30 pm EDT