Lock gates maintain a water-tight seal by fitting very closely to the shaped stone work along their hinge line or 'heel' and their bottom edges against wooden blocks bolted to the lock structure forming a 'cill'.
The position of the cill is often marked in paint to warn boaters to keep clear when descending a chamber; avoiding the risk of the stern being caught on the cill.
Recently, at the tailgate of Lock 13W, the bolts securing one of the cill timbers came loose and as the lock filled, pressure of water under gate forced the cill block up and washed it several metres downstream.
The first photo shows the position of the missing wooden block from the lower cill.
The block was retrieved and can be seen propped against the stop planks which form a temporary dam, allowing the chamber to be drained and repairs to take place.
At Lock 17W, the top gate seal is made by thin piece of wood fixed to larger wooden block.
Recently, a boat left the lock while the pound above was low and with limited freeboard, accidentally caught the cill, breaking the thinner piece of wood (see photo, right), thus compromising the seal.
Consequently the lock chamber would not empty easily (with water gushing under the gate) and more seriously, a boat on its descent would be in danger of being swamped.
A similar problem happened with the upper cill of Lock 20E near Slaithwaite, also in June. All of these problems led to stoppages until the repairs were carried out by British Waterways staff.
[Martin Clark]
