Cill Related Sinkings – A Reminder

 There have been 25 sinkings related to cill hang-ups in the past 10 years. Many hire operators and private boaters are aware of the risks but cill related sinkings continue to happen. Another incident occurred recently when a hired narrowboat sunk negotiating a lock. The incident happened when travelling downhill through the lock chamber.

sunk boat

It is essential that proper control is maintained over the boat and that it is kept forward of the top lock gate cill. The extent of the cill is marked by white lines on the copings with the word ‘cill’ stenciled on and a warning sign is placed on the gate.

Failure to keep forward of the cill marker can result in the boat sinking at the front and raised out of the water at the stern. This can happen quickly and can result in the boat to sinking or capsizing in seconds.


Handovers to hireboaters should emphasis the proper navigation through locks and the potential risks if the boat is not properly controlled. Private boaters should ensure they remain vigilant to the risk of cills and becoming hung up as the lock empties.

The Boater’s Handbook carries advice to avoid and recover from lock hang-up incidents


Floating freely?

As the water level rises or falls, keep a continual check on your boat.

Is your rudder caught on the cill? (Going downstream)

Close the bottom gate paddles to stop the water falling further. Slowly open the top gate paddles to refill the lock. Check for damage.

Is the side of your boat caught against the lock wall? (Going either upstream or downstream) Refill the lock and check for damage.

Is the front of your boat caught on the top gate? (Going upstream)

Close the top gate paddles to stop the lock filling. Open the bottom gate paddles to allow the water level to fall.

If you’re sharing the lock with another boat, is there a safe distance between you? (Going either upstream or downstream) Use ropes looped round the bollards to keep you in position.

Are your ropes snarled or too tight to let your boat move down freely?

(Going downstream) Slacken them off if you can. If not, refill the lock

The cill position will be clearly marked on the lock coping stones and lock wall and this sign will be on the gate balance beam.









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