Photo of a boat that has sunk after being hung up on the cill on the Bath Flight, courtesy of Canal & River Trust.
When going through locks, to prevent your boat getting hung up on the cill, remember to maintain control of the boat and ensure it is kept forward of the top lock gate cill. Warning signs are placed on lock gates and the word 'Cill' and white lines are marked on the walls of the lock. If a boat is not kept in front of this marker it can result in the boat sinking within minutes.
There is more advice on how to prevent and recover from a lock hang-up in the Boater’s Handbook.
Photo below shows a cill marker on a lock chamber wall, courtesy of Canal & River Trust.
Boats can also get caught on lock gates or stonework when going up or down a lock.
It’s a good idea to always ensure that your boat is moving freely and get ready to close the paddles you are using and open the paddles at the other end of the lock to correct the situation.