Page 4: Variations
Not all locks work exactly as described previously, and the terminology changes, too ...
Single gates on narrow canals (locks approx. 7 feet / 2.1 m wide)
- A few narrow locks imitate wide locks in having paired gates at both ends (eg Bosley, on the Macclesfield canal)
- On most English narrow canals however, the upper end of the chamber is closed by a single gate the full width of the lock. This was cheaper to construct and is quicker to operate, as only one gate needs to be opened.
- Some narrow locks (eg on Birmingham Canal Navigations ) go even further. They have single gates at the lower end also. This speeds up passage, even though single lower gates are very heavy (heavier than a single upper gate, because the lower gate is taller) and the lock has to be longer (a lower gate opens INTO the lock, it has to pass the bow or stern of an enclosed boat, and a single gate has a wider arc than two half-gates).
Alternate forms of gates
- Steel Gates. Some locks (particularly modern commercial ones) use gates made of steel, but even very large locks still use essentially the same swinging gate design, with the exception of some low-head locks that use sliding gates (eg Kiel Canal).
- Guillotine Gates. Some locks have vertically moving steel gates - these are quite common on river navigations in East Anglia. Sometimes just one of the pairs of swinging gates is replaced by a guillotine: for instance at Salterhebble Locks, where space is restricted by a bridge.
Alternate paddle gear
- Some manually-operated paddles do not require a detachable handle ( windlass ) because they have their handles ready-attached.
- On the Leeds and Liverpool Canal, paddles are raised by turning what is in effect a large horizontal wingnut (butterfly nut) lifting a screw-threaded bar attached to the top of the paddle.
- On the Calder and Hebble Navigation, some paddle gear is operated by repeatedly inserting a Calder and Hebble Handspike (length of 4" by 2" hardwood) into a ground-level slotted wheel and pushing down on the handspike to rotate the wheel on its horizontal axis.
Some locks are operated (or at least supervised) by professional lock keepers. This is particularly true on commercial waterways, or where locks are large or have complicated features that the average leisure boater may not be able to operate successfully. For instance, although the upper Thames (England) is almost entirely a leisure waterway, the locks are usually staffed.
On large modern canals, especially VERY large ones such as ship canals, the gates and paddles are too large to be hand operated, and are operated by hydraulic or electrical equipment. Even on smaller canals, some gates and paddles are electrically operated, particularly if the lock is regularly staffed by professional lockkeepers. Powered locks are usually still filled by gravity, though some very large locks use pumps to speed things up.
The construction of locks on rivers obstructs the passage of fish such as trout going upstream to spawn. Measures such as a fish ladder are often taken to counteract this.
Page 1 - Introduction & use of locks...Go
Page 2 - Basic construction and operation...Go
Page 3 - Details & Terminology...Go
Page 4 - Variations...(Current page)
Page 5 - Illustrations...Go
Page 6 - History & Development...Go
Page 7 - Use of water...Go
Page 8 - Alternatives...Go