A narrowboat beginner’s guide to a “typical lock”

There is no such thing as a typical lock. Even on the same canal, each lock has some individuality and it’s amazing the variety you’ll encounter, but I’ll try to imagine what a typical lock might look like while pointing out the differences you might find on various canals.

Narrow vs wide

Most canals are narrow, meaning locks on that canal are just wide enough to accommodate (sometimes just barely) a seven-foot-wide narrowboat (most boats are about six feet, 10 inches wide). So we’ll consider a narrow lock to be typical. Most narrow locks are just long enough for a 60- or 70-foot-long boat, but don’t worry about this. Your boat hire won’t rent a boat too long to fit in the locks of the canal(s) the boat hire serves.

On narrow locks, most likely the uphill gate will be a single gate with ground paddles on either side of the lock chamber. These paddles open and close underground sluices that let water from the pound (the stretch of water between locks) into the lock chamber. On a bog standard narrow lock, those paddles will be raised and lowered by rack and pinion gearing turned by a metal L-shaped windlass key or handle (provided with the boat). On some staircase locks, you might encounter hydraulically operated paddles with a housing resembling a tall, black-and-white fire hydrant, probably sitting at a jaunty angle.

Wide locks, of course, can accommodate boats wider than a standard narrowboat and usually can allow two narrowboats at a time to pass through. A single narrowboat in a wide lock unfortunately is a lot harder to control and of course it’s not as economical in terms of water consumption. There’s not really a hard and fast definition of how wide a wide lock is, but there’s also no standard width for a wide beam barge. Typically wide beam barges are about 10 to 12 feet in width. Again, you’re unlikely to be rented a barge too wide to pass through the locks on a particular canal.

Mitered vs flat

The rear gate of a standard narrow lock will probably be two mitered gates with paddles in the gates, and the paddles will probably be raised/lowered by rack and pinion gearing mounted to the balance beams that move the gates. Some gates with unusually heavy paddles will have hydraulic cylinders to raise/lower paddles. These are still usually operated by a windlass key, but some locks will have permanently applied wheels to turn the hydraulics.

On some narrow locks, the downhill gate might be a single gate. All the locks on the South Stratford Canal have single gates. Every wide canal lock (to my knowledge) uses a pair of mitered gates at either end. I haven’t encountered any, but I believe there are narrow locks with mitered gates on both uphill and downhill sides.

Ground paddles vs gate paddles

Some locks have gate paddles on both uphill and downhill gates and I suppose there are locks with only ground paddles, but in general there are ground paddles on the uphill and gate paddles on the downhill side. Paddles, incidentally, are usually large wooden (once elm, now oak) shutters. They weigh quite a lot and it’s important not to let them drop uncontrolled as it might damage the paddle.

Some wide locks will have both ground and gate paddles to fill and empty lock chambers more quickly. Generally it’s a good idea to open the uphill ground paddles before the gate paddles—you want the front or rear of the boat raised enough to avoid being swamped by water coming in through the gate paddles.

Deep vs shallow

I’m not sure what’s the average depth of a canal lock, but if I had to guess it’s 8–9 feet. The deepest lock is the Tuel Lane lock on the Rochdale Canal, dropping 19 feet 8 inches or six meters, although the effect is lessened by being a wide lock. Unusually deep locks often occur when a single lock replaces two previous locks. I can’t say what the shallowest lock is but I know some locks, like the Graham Palmer lock on the Montgomery, drop only a matter of inches.

Balance beams

Gates are moved by the attached balance beams. These are long wooden beams, perhaps a foot square in cross section and angled slightly upward. They are often moved by putting a backside against the beams, but a handle is provided on top to pull the beams away the side of the lock chamber. Some balance beams are bent because of some restriction, usually a wall or other obstruction, and some locks have no balance beams altogether, for the same reason. The gates must be opened/closed with gearing.

Bridges and walkways

One of the challenges in turning a lock is to get from one side of the lock chamber to the other because the paddles are on either side. Usually one crosses a narrow walkway attached directly to the outside face of the gates. On the uphill side, that means you’re crossing only about a foot above the surface of the water, but on the downhill side you might be facing a ten-foot drop. There are handrails attached to the balance beams and there is a non-slip coating applied to the walkway, but it can still be an exhilarating experience. On a narrow lock using single gates, the walkway might be the top of the balance beam.

You might be lucky, however, and find a catwalk or bridge crossing the downhill side of the lock, making it easy to get from one side to the other. Locks and bridges often go together, but the magnificence of the bridge varies. In some cases the bridge is little more than a catwalk spanning the downhill side, but often there’s a stone bridge. Out in the countryside, this might be a footbridge farmers use to cross cattle, but it’s quite common near a major road. There will still be a walkway attached to the gates even though the stone bridge provides a way to cross.

There are even some locks with a swing or lift bridge next to the lock and even the occasional movable bridge spanning the lock chamber. You’ll probably find a sign next to these bridges indicating whether or not you should leave these bridges spanning the canal as you leave.

Ladders

Locks will always have ladders inset into the walls of the chamber, both for the safety of boaters who fall into the water and for the use of one-person boat crews. Lock ladders, however, are usually slippery because the rungs are often underwater The ladders will be on one or both sides of the lock chamber and often offset, about a fourth of the way from the gate. This makes it easy for a person standing at the tiller to climb up and turn the lock. (On locks with the ladder in the middle, a single person will have to walk on the roof of the boat to reach the ladder.)

Brickwork, grass, steps

A narrow lock in the middle of the countryside probably has a minimum of surrounding brickwork, just the stones and brick of the lock chamber itself. You’ll find well-worn grass next to these locks, but there will still be bricks embedded in an arc under the balance beams to provide traction while pushing or pulling the beams. A country lock may just have the packed sand or gravel towpath descending the downhill side of the lock, but a grander lock might have brick or stone steps (very common on staircase locks).

One convenience on some locks are stone or brick steps on the downhill side, allowing boat crew to leave or return to the boat without needing to first moor. It does take some dexterity, however, to return to the boat while the boat is moving.

Rings, bollards or posts

There’s always some means of loosely securing a boat within a lock, generally for the convenience of a single person handling a boat. You would pass the centerline of the boat through a ring or around a bollard or post. I’ve never had to secure a line around a square post and wonder if it’s as convenient as a bollard. A ring, bollard or post makes it easier to secure a single narrowboat passing through a wide lock. The water rushing into a wide lock through the paddles can buffet a single narrowboat in a wide lock.

There are always rings, bollards or posts before a lock, both uphill and downhill, to let crew off to turn the lock. Usually the towpath side also has stones or timbers protecting the bank as well.

Straight, curved or diamond-shaped

The overwhelming majority of lock chambers are straight sided, but there are some curious exceptions such as the two diamond-shaped locks on the Oxford Canal. The odd shape reportedly let the lock hold more water for the convenience of subsequent downhill locks. The same is probably true of curved locks chambers. I’ve yet to encounter a diamond or curved lock chamber, but it looks as if it would be difficult to keep a boat centered in one.

Diversion weirs and side pounds/ponds

Sometimes there isn’t enough water in the uphill pound to provide water to turn a lock and the reasons for this and strategies to cope with this problem will be addressed in a future article. The most common way to ensure that each pound has enough water is the diversion weir that runs beside a lock. This is usually just a shallow trough next to the lock that allows excess water to flow around the lock even when the gates are shut. This ensures that the uphill pound does not flood and it supplies the downhill pound with water. Not every lock has a diversion weir; they’re most common next to narrow locks or closely spaced locks. Of course some water makes it past even closed lock gates because paddles and gates invariably leak.

Side pounds are also used to ensure a plentiful supply of water and this is most obvious on the tightly packed flight of 16 locks on Caen Hill near Devises, Wiltshire. The pound between locks is very short and large side pounds increase the storage capacity.

Side ponds are a similar concept but they’re directly connected to a lock chamber. The idea is that while emptying the lock chamber, that water is first diverted to the side pond. (A diversion weir also directs water into the side ponds.) When the lock chamber needs to be filled, the water in the side pond is used before opening the uphill paddles. Water entering or leaving the side pond is controlled by a separate paddle and gearing. At the moment, only the Hanbury locks on the Droitwich Canal still use side ponds, although there are disused side ponds on locks on the Macclesfield Canal.

Anti-vandal safeguards

Many locks, especially those in urban area, are fitted with anti-vandal safeguards, usually requiring a special key to unlock the paddle gearing. The most common is the handcuff key, which looks nothing like a modern-day handcuff key (it more closely resembles the key used to open “darby” handcuffs). These keys basically release a latch that makes it possible to turn the spindle that raises/lowers the paddles. The gates themselves are usually not locked because if you can’t open the paddles, you’ll never be able to open the gates. However you might find additional security measures applied to a lock gate to prevent anyone other than canal authority workers from turning the lock. The Canal & River Trust, for instance, limits access to the Montgomery Canal because of its rural nature and protected habitats.

Signs and numbers

Every lock I’ve encountered has been identified with the number of that lock painted on the balance beams. The numbering schemes of locks varies depending on what end the canal was started, whether the canal joins or intersects with another canal and whether the segments of the canal were completed by different companies. Most every lock has a name, sometimes forgotten, often nonsensical or no longer appropriate. Generally the top (highest) and bottom (lowest) locks of a flight will have a sign proclaiming that status, but many locks are nameless unless you view the maps maintained by the appropriate navigational authority. You’ll also usually find a sign indicating when the lock gates were last replaced.

Staircase and lock flights

Staircase locks are definitely not typical, although you’ll often find that each step of a staircase locks is a typical lock. It’s just that the bottom gate of one lock is the top gate of the next lock (or vice versa). Staircases are rare and even rarer are canals with multiple staircases. In contrast, lock flights are common and often provide the most examples of a typical lock. Usually every lock in a flight is identical to every other lock in the flight and most canals have at least one flight. (A lock flight is nothing more than a series of locks spaced closely enough that they’re considered a unit.)

So what is a typical lock?

In my mind, a typical lock is to be found in the countryside, the canal running beside farm land and the towpath bordered by blackberry bushes—where it’s not bordered by stinging nettles. A few trees growing along the opposite bank of the canal shelter cows placidly standing and observing the lock activity. There’s undoubtedly a stone bridge across the canal not far from the lock but a road no longer connects to the bridge. Perhaps it was once used to move cattle from field to field but is no longer needed for that purpose and there’s no break in the bushes along the towpath allowing access. Stones or timbers line the canal along the towpath on the approach to the lock and rings or bollards provide temporary mooring for three or four boats.

This far in the countryside, there is no brickwork leading up to the lock—which isn’t missed because it‘s not a particularly deep lock—and the dirt towpath gently climbs up the bank of the bottom gate. It’s a narrow lock with a single uphill gate and a pair of mitered downhill gates. The lock chamber is lined with brick with larger stones lining the edges, but otherwise grass grows right up to the lock chamber. White metal bollards, sunk into concrete, are on one side of the lock chamber to hold a boat in place. There’s a moderate cill projecting into the chamber next to the top or uphill gate.

The lock is controlled by ground paddles next to the top gate and gate paddles on the bottom gate. Unfortunately there is a plastic grocery bag wrapped tightly around the winding gear of one of the top paddles, which draws attention to the fact that the pawl, which prevents the rack and attached paddle from dropping, is broken and won’t engage the ratchet. The metal tooth of the pawl has sheared off after possibly hundreds of years of service. Only one working paddle means it will take a while to fill this lock chamber. Fortunately the gate paddles, also raised by rack and pinion gears, are still working, if a little stiff to turn.

One of the balance beams is noticeably different; it’s missing its black and white paint indicating the beam has recently been replaced. The beams sometimes rot and break and sometimes vandals are to blame. It was probably an emergency repair and there’s probably a sad story of a boater unable to turn the lock.

Crossing this lock is accomplished by using the walkways attached to the gates. Unfortunately the non-slip coating is missing in a few places, but the handrails attached to the balance beams make it easy and safe to cross. Not too surprisingly, there’s no large arc of bricks under the balance beams, just a quarter circle of brick directly under the path of the handles attached to the beams.

One of the nice features of this lock is the sign giving the name of the lock, a little surprising as it’s just an anonymous lock in the middle of a short flight. The lock number is on a plaque on the balance beam, but it adds a personal touch to know the name. An additional sign also lists the date the lock gates were replaced, and that date is twenty years past, which explains why the gates are badly leaking. There are offset ladders on either side of the lock chamber. There is not a diversion weir to allow water to bypass the top gate and continue to the next lock in the flight.

Another thing that makes this lock a little atypical is a dilapidated wooden bench next to the lock chamber. The bench looks to be 50 years old, but a plaque dedicates it to the memory of someone who died five years before. It’s subtle reminder of how timeless a canal lock can be. Many were built two hundred years earlier and some survive today almost unchanged except for the replacement of lock gates. Anything added to a lock quickly comes to look as ancient and as serviceable as what was there before. Each lock is typical and yet each is unique.