Avoiding lock hang ups and sinkings

Every year, lock cills catch boaters unaware, no matter how experienced they are. Once a vessel’s caught on a cill it can cause the rudder to pop out of the cup, which is easily resolved. However in many cases it results in damage to the skeg, rudder and bearings, and the boat needing to be towed and dry-docked to have the damage repaired. There’s also a risk of taking on water and the boat sinking.

Lock cill in a broad lock

River Canal Rescue chief rescue co-ordinator, Pete Barnett, explains what to do if your boat’s caught on a cill:
“Cills protrude below the water, close to the top gates of most canal locks. If you’re travelling downhill in the lock chamber and your stern, ie rudder, gets caught on the cill, when the water recedes only the bow of your boat will lower with the water level, leaving the stern raised up. Sinking or capsizing can happen in seconds.

If you’re aware the stern’s caught, close the bottom gate paddles to stop the water receding further and slowly open the top gate paddles to refill the lock. Hopefully there will not be any damage, or at least you will be able to remove it from the lock and get some technical assistance.”

But if the boat has suffered serious damage and you can’t remove it from the lock Pete recommends that you ensure everyone in your crew is safe and then contact the Canal & River Trust who will send out a team to assess the site, contain pollution and ensure your boat isn’t causing a navigational hazard. If your boat’s on the River Thames or other river navigation you may need to contact the Environment Agency if the CRT does not have jurisdiction. In either case, the EA and CRT should work in tandem with recovery specialists to get your boat moved as quickly as possible.

If you are on a hire boat you must inform the hire firm. If you own the boat you must contact your insurer who will ask for a specialist recovery firm to salvage the craft. It’s likely the RCR Canal Contracting team will appear on the scene as they’re authorised to handle claims for most of the UK’s leading boat insurers.

Once the boat is raised, the cause of the sinking will need to be identified by an engineer or surveyor before the claim’s accepted. All contractors have to meet the CRT’s/EA’s risk management requirements, otherwise they’ll not be given permission to raise the vessel.

Not all lock sinkings are caused by the boat stern sitting on the cill while descending a lock.

A boat going uphill can get its bow or bow fender stuck under a projection on the top gate, leaving the stern to rise with the water level. If this happens, close the top paddles to stop the water level rising and open the bottom gate paddles to allow the water level to fall until the boat can be moved away from the top gate.

Boats can sometimes jam on a projection from a lock wall, especially if your side fenders have not been lifted before locking. When it happens you should drop all the paddles and assess the situation. Then, if the boat is sitting on top of a projection slowly let in more water, or drain water if it is caught beneath a projection.

In broad locks a narrowboat may jam by twisting across the lock, so keep boats roped close to the wall. Two narrowboats sharing a lock canal also become twisted and jam. Drop all the paddles and assess what is happening. Then slowly add or remove water until the boats are free.

If your ropes get jammed or tied when the boat is descending a lock it can cause a boat to get hung up and possibly jammed by the boat listing over. Let water in slowly to see if it frees the boat.

Boats have also been sunk by boaters opening gate paddles too early and swamping the foredeck. If a lock has gate paddles always open the ground paddles first and only open the gate paddles when the water from the gate paddle is below the hull level.

Jammed boats can be under a lot of pressure from the water and their own weight, and this can release violently. Don’t try to force a boat free free using boat poles or ropes. Equalise the water level until the boat(s) floats normally.

Most people consider the safest position in a lock for a leisure boat is in the middle of the lock, not close to the top or bottom gates. Many boaters will use a centre rope to help the engines maintain a central position. See our Safe Locking advice pages.

Thanks to River Canal Rescue for most of the information on this page.