As a man-made channel with managed water levels, a canal can’t simply flow downhill like a river. Instead, it uses a series of water-containment chambers called locks. These can vary in length, width and depth (see Narrowboat or barge? Canal boats explained), from a narrow lock that will only take a single 60-foot narrowboat to huge automated locks that can make small leisure boats feel like matchsticks. The specific mechanisms can also vary from lock to lock but in all cases, the underlying principles for how to operate a lock remain unchanged.

How to operate a lock

Locks are a pleasure once you know how to use them.


A lock is simply a chamber with gates at both ends. In each gate are paddles (or sluices) that can be lifted and lowered in order to allow water into and out of the lock. When you drive into an empty lock and fill it with water, your boat will be lifted to the higher level. When you drive into a full lock and empty it, your boat will be dropped to the lower level. When the water level in the lock matches that on the other side of the closed gate, you can swing the gate open and continue your journey on a new stretch of canal. All you really need to master, therefore, is how to open and close the gates and paddles, how to obey canal etiquette and how to stay safe while you do it (and avoid getting into a canal boat disaster like this).


Making your approach

Reconaissance – how to operate a lock

Always despatch your reconnaissance man to go ahead and investigate the state of the lock.

Whether going up or down, reconnaissance is an important part of lock work. Drop your lock man on the towpath and send him ahead to identify whether the lock is empty or full. If you want to go downhill and it is full, you can just open the gates and drive straight in. If it is empty (and there is no boat attempting to come up) you will need to signal to the boat that this is the case and then fill it. Ensure the gates are closed and the lower paddles are shut and then open the upper paddles to allow water in.

Obviously, the opposite applies if you are attempting to go uphill. Send a man ahead and if it is empty, drive straight in; if it is full, open the lower paddles (gently) to empty it while ensuring your boat is comfortably tied alongside so it isn’t bullied out of shape by the water flow (for tips on pulling off this manoeuvre, see: How to drive a narrowboat). Whether going up or down, however, the reconnaissance party should always identify whether there is a boat approaching the lock from the other direction. If there is, then the boat with the water level already in its favour should be given right of way.


Managing the water

Most locks use manually operated rack and pinion systems. You use a windlass (a metal L-shaped device with a square socket to fit onto the winding knob) to lift and lower the paddles. When you wind the paddles up to let water in, do so bit by bit and keep an eye on the boat to see how it is affected by the turbulence.

When the paddles are up, you can engage the safety catch to stop the gears slipping (mind your fingers here) and disengage your windlass. Once the water level has equalised and you are ready to return the paddles to the closed position, do so by releasing the safety catch and winding them back down with your windlass. Don’t just let them drop, as you can damage both the gearing and the paddles. When you have finished with the lock, remember to check for an approaching boat, as it is likely to want to drive straight into the open lock. Otherwise, lower the paddles and close the gates behind you.


Downhill hazards

When you head downhill, the key hazard is the cill. This is a solid protruberance on the inside of the upper gate that can stick out by as much as five feet. It is below the water when the lock is full, so you will only see it as the lock empties. It is therefore vital that you use your engine to stay ahead of the clearly painted cill marker on the lock walls at all times. If you don’t you will get your stern caught and find yourself at an increasingly alarming angle as the lock continues to empty.

Avoiding the cill – how to operate a lock

Use your engine to stop short of the forward gate and keep it running to help maintain position.


Uphill hazards

When you head uphill, the key hazards are turbulence and water ingress at the bow. In order to minimise these, you should position the boat a decent distance back from the front gates and make sure the windlass operator opens the paddles very steadily. Again, use the engine to keep your position steady and (in wide locks) use a line looped around a bollard at bow and stern to prevent the boat clattering sideways into the opposite wall.

Cill marker – how to operate a lock on a canal

Stay alert at the helm and don't forget the cill marker.


Top ten tips

Gates and paddles – how to navigate a lock

An empty lock illustrates the simplicity of the gates and paddles system.

(1) A lock is full of heavy, unyielding machinery so avoid rushing and set aside at least 20 minutes to make your way through.

(2) Engine and water noise can make communication difficult, so a simple signing system between helmsman and lock operator can be very useful.

(3) As regards etiquette: allow a boat going in the same direction to share the lock; avoid queue jumping; and don’t loiter in the spaces on either side of the lock.

(4) Line yourself up early, take it slow and use your engine to stop in the lock, rather than simply smashing into the gates.

(5) While well-serviced gates can be swung with minimal effort, a build up of silt and debris at the end of a season may mean extra elbow grease and some gentle clearance with a boat hook is required.

(6) Stay at the helm with your engine running for the entire process, and make sure you do not stray aft of the cill marker or too close to the gates.

(7) Lift and lower the paddles steadily and under control so that water movement in and out of the lock is measured rather than frantic.

(8) Assuming nobody wants to drive into the lock as you leave, make sure you close the gates and leave the paddles fully shut.

Moving on – how to operate a lock on a canal

Job done - just remember to check for approaching boats before shutting the lock back up.

(9) Locks are dangerous places, so whether it’s a legal requirement or not, do as the professionals do and wear a proper lifejacket.

(10) Read the excellent ‘Boater’s Handbook’ before you go. It’s full of very accessible illustrations and it’s free to download from the CRT website (

For more on the joys of inland waterway boating, see: 10 top tips for enjoying a narrowboat holiday and Your guide to buying a narrowboat.

Written by: Alex Smith
Alex Smith is an ex-Naval officer, with extensive experience as a marine journalist, boat tester and magazine editor. Having raced as a Pilot in the National Thundercat Series and as a Navigator in the inaugural Red Sea RIB Rally, he has now settled in the West Country, where he lives and works as a specialist marine writer and photographer from his narrowboat in Bath.