Chapter 3: How a Canal Lock Works

A = Upper Gates B = Lower Gates C = Lower Gate Paddles D = Gate Recces

E = Foot Holds F = Gate Arms K = Upper Gate Paddles

If you look at the plan view above, you will see that the lock gates (A & B ) close in a V shape and that the V points to the highest water level. This ensures that when closed, the weight of the water keeps them tight shut and watertight. In the bottom of each gate is a paddle or valve to let water in and out of the lock ( K & C ). These are opened by turning a handle on the mechanism on top of the gate or at the lock side. Each gate has a long heavy arm at the top which you push to open them. You push by putting your back against the arm ( F ) and pushing with your feet on the ridges ( E ). There are recess’s in the lock walls ( D ) for the gates to fit into when open, out of the way of the boat.

A = Upper Gates B = Lower Gates C = Lower Gate Paddles

G = Bottom of Lock and Lower Canal H = Bottom of Upper Canal

K = Upper Gate Paddles J = Water Duct from Upper Canal into Lock

So how does it work. Like most things, it’s easy once you know how.

Imagine a longboat ( they can be 69ft long ) sailing along on the lower level at the right of the drawing. You tie up and go to the lock. You close the valves (K) and open the lower valves© if necessary. When the water level in the lock is the same as the lower canal, you open gates (B) Then you can sail your boat into the lock.

Next you close gates (B) and then close valves©. Going to the other end of the lock, you open valves (K). Water from the higher canal then flows down pipe (J) and starts to fill the lock. Your boat rises up as the lock fills until it is level with the water in the higher level of the canal.

You can then open the upper lock gates (A) fairly easily ( as long as you are reasonably fit! ) and sail your boat out of the lock to continue your journey. It is etiquette to close the valves before you go.

Most locks will take two boats side by side, but there are single width locks on smaller canals.

If you’ve never seen one in action, it’s well worth taking a walk by your local canal.

A lock uses a lot of water and is very time consuming. There have been alternative ideas over the centuries such as inclined planes and lifts. Two lifts still in use are the magnificent Anderton Lift near Northwich in Cheshire and the spectacular Falkirk Wheel in Scotland. Both of these operate on the same principle as an ordinary pedestrian lift, except that their doors are watertight.

The boat sails into the lift, the watertight doors close and the lift goes up, or down ( or in the case of the Falkirk Wheel, round ) whilst the boat floats stationary in the lift. When the lift stops, the watertight doors open, and you sail out at the new level.

The Falkirk wheel replaces a staircase of eleven locks. ( A staircase of locks is simply a hill of locks, one lock immediately after another, you sail out of one, then sail straight into the next lock. Once you start up, or down, you have to keep going, so a set of eleven could be a half day’s hard work.) It’s also one way, so once you have started up or down, other boats can follow you, but no one can go the other way. There is no such thing as rushing on a canal.

The Falkirk wheel would move a boat the equivalent of eleven locks in half an hour or less and save ten full locks of water every time.

Both the Anderson Lift and the Falkirk Wheel operate tourist boats so you can enjoy the experience. You will find pictures and information on their web sites or on Utube.