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Canal Locks: Variations

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Variations exist for types of locks and the terminology used for them.

  • Single gates on narrow canals locks approx. wide
  • On most English narrow canals, 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 with a small crew, as only one gate needs to be opened.
  • Some narrow locks e.g. 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 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.
  • A few narrow locks imitate wide locks in having paired gates at both ends. An example is the Bosley Lock Flight on the Macclesfield Canal.

  • Steel gates. Steel gates and/or balance beams are frequently used nowadays, although all-wooden versions are still fitted where appropriate.
  • Swinging gates. Even very large steel-gated locks still can use essentially the same swinging gate design as small 250-year-old locks on the English canals. On English canals, steel gates usually have wooden mitre posts as this gives a better seal.
  • Sliding gates. Some low-head locks use sliding steel gates see 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 to swing the balance beams of bottom gates of the lowest lock was restricted by bridge widening. On the River Nene most locks have this arrangement as in time of flood the top mitre gates are chained open and the bottom guillotines lifted so that the lock chamber acts as an overflow sluice. Guillotine gates are also used on the downstream side of larger locks such as the 23m Bollène lock on the River Rhône, the aperture being large enough for a boat to travel under it.
  • Vertically rotating gates American usage: Drop gates are gates which, when open, lie flat on the canal bed and which close by lifting London Flood Barrier. Some of these were installed on the Chesapeake and Ohio Canal in the congested 7 Locks area since they could be operated by one man and also could speed up traffic.
  • Rotating-sector gates. Some of these work very like traditional swinging gates, but with each gate in the form of a sector of a cylinder. They close by rotating out from the lock wall and meeting in the centre of the chamber. Water is let in or out by opening the gates slightly: there are no paddles or other lock gear. The lock at Limehouse Basin, which gives access to the River Thames, is an example. A dramatically large one can be seen at the Rotterdam flood defences huge flood gates. There is a different type at the sea lock on the Ribble Link: this is a rising sector gate, which has a horizontal axis: the gate drops to the bed of the river to allow boats to pass.

  • 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 there is a variety of different lock gear. Some paddles are raised by turning what is in effect a large horizontal wing nut butterfly nut lifting a screw-threaded bar attached to the top of the paddle. Others are operated by lifting a long wooden lever, which operates a wooden plate which seals the culvert. These are known locally as "jack cloughs". Bottom gate paddles are sometimes operated by a horizontal ratchet which also slides a wooden plate sideways, rather than the more common vertical lift. Many of these idiosyncratic paddles have been "modernised" and they are becoming rare.
  • 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.
  • On some parts of the Montgomery Canal bottom paddles are used in place of side paddles. Rather than passing into the lock through a culvert around the side of the lock gate, the water flows through a culvert in the bottom of the canal. The paddle slides horizontally over the culvert.

  • Composite locks. To economise, especially where good stone would be prohibitively expensive or difficult to obtain, composite locks were made, i.e. they were constructed using rubble or inferior stone, dressing the inside walls of the lock with wood, so as not to abrade the boats. This was done, for instance, on the Chesapeake and Ohio Canal with the locks near the Paw Paw Tunnel and also the Chenango Canal Because the wood would swell making the lock space smaller or rot away, the wood was often replaced by concrete.

  • Lock keepers. Main article: Lock keeper 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 Thames above Teddington England is almost entirely a leisure waterway, the locks are usually staffed. Only recently have boaters been allowed limited access to the hydraulic gear to operate the locks when the keeper is not present.

  • Powered operation. 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 lock keepers. On the River Thames below Oxford all the locks are staffed and powered. Powered locks are usually still filled by gravity, though some very large locks use pumps to speed things up.

  • Fish Ladders. The construction of locks or weirs and dams on rivers obstructs the passage of fish. Some fish such as trout and salmon go upstream to spawn. Measures such as a fish ladder are often taken to counteract this.

  • Weigh lock. A weigh lock is a specialized canal lock designed to determine the weight of barges to assess toll payments based upon the weight and value of the cargo carried. The Erie Canal had a weigh locks in Rochester, Syracuse, and West Troy New York. The Lehigh Canal also had weigh locks see photo on right.

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