A lock is a device for raising and lowering a boat, ship or other craft between stretches of water which has different levels on canals and rivers, effectively making the river navigable..
There are many different types of locks but all have the same principle of use.
Locks on canals and rivers in UK are now all Pound Locks.. The lock has a chamber with gates and paddles at both ends where the level of the water can be controlled. Some locks in the early days were called Flash Locks and had a single gate. On “narrow” canals, locks are big enough for just one narrowboat at a time. On the “broad” canals and most rivers, vessels of much larger dimensions are accommodated.
The Chamber is the main feature of the lock as it is (or should be) a watertight enclosure constructed of masonry, brick, concrete or sometimes steel. An average lock rise/fall is around 6-7 ft (2 metres), with Fenny Stratford (Grand Union) at 1 ft and Bath Deep Lock (Kennet & Avon) being over 19 ft deep.
Boats enter through a pair of gates at either end. The gates seal the chamber at both ends and are usually made of oak or elm or sometimes steel. When the gates are closed the pair meet at an angle like a chevron pointing upstream and only a small amount of water is needed to squeeze the gates together. A lower gate is always taller than the upper gate because the lower gate needs to seal off the whole chamber whereas the upper gate has only to be tall enough to close off the upper pound of water.
Pound locks were first used in China between 960 and 1279AD. In Europe a type of pound lock was built in 1373 in the Netherlands.
Locks bypass an obstruction such as a rapid, dam or weir. In large scale river navigations such as the River Thames, the locks are used together with the weirs. A weir will increase the depth of a shallow stretch of water and the lock will be either built in a gap in the weir or at the downstream end of an artificial cut.
When we cruise the Kennet and Avon Cana , we see some unusual locks. There are two remaining turf sided locks, seen at Garston Lock and Monkey Marsh Lock. Both were originally built between 1718 and 1723. They need significantly more water to fill them as part of the sides are walls like other locks but part of the sides are partly filled with vegetation. Steel railings and posts ensure that boats stay in the centre of the lock. These locks are Grade2 listed.
Sheffield Lock in the parish of Burghfield in Berkshire was built around the same time and was originally a turf sided lock but it now consists of brick chamber walls of 11 scalloped bays. This lock is also grade 2 listed. There is a similar lock construction at Aldermaston.
Once in a lock, to raise or lower the water level, ‘paddles’ are used, using a ‘windlass’ or ‘lock key’. Paddles can be of various types, with some located in the gate and some on the lock side. Either may be completely manual, hydraulic assisted or electric powered. We like electrically operated locks!
Some flights of locks form a Staircase, where the top/bottom gates of a lock are also the bottom/top gates of the next chamber. Good examples are at Foxton and Bingley. Boats travelling in the opposite direction must wait for boats to complete all the locks before it becomes their turn.
On some rivers the gates are known as doors. And at some locks, the gate may be a guillotine type of steel construction. On these, beware of drips!
The northern part of the Grand Union Canal from Calcutt heading towards Birmingham (previously the Warwick and Napton Canal) has hydraulic-assisted paddles. These are posts where you raise the paddle with your windlass, then attach a C-shape clip to the spindle to hold it in place. Although easier to operate than most manual locks, they do have a tendency to lose pressure, so you need to keep an eye on the falling rod and know the paddle is closing before it needs to. Then wind it a bit further!
River Thames Locks between Teddington and Godstow, just above Oxford, are all electrically operated. Normally, Lockkeepers are in attendance, but occasionally locks are on “self-service”, so boat crews must operate the buttons themselves. It is a relatively straight-forward process, but occasionally operators can “confuse” the lock mechanism by repeatedly pressing, holding in the buttons and randomly pressing, expecting the mechanism to understand what the operator is expecting it to do. At that point, the mechanism says “No more” and shuts down. You then must wait about 45 minutes for the system to re-set.
Above Godstow, starting at Kings Lock, the locks are all manual. Usually the friendly Thames lockkeeper will be in attendance, but at lunch times or when keepers are attending the weirs or doing another task, self-service rules apply. The mechanism on the manual locks is a wheel to lift the paddles and an aluminium pole to pull or push the other gate. Incidentally, Kings Lock is the most northern point of the River Thames – so now you know!
We have found all Lockkeepers on the Thames to be helpful and friendly, but must admit that above Oxford, not only the personality of the river changes. The keepers do too!
Limehouse Lock onto the Thames is operated by Canal & River Trust staff. The lock gates here do not have paddles, and the gate resembles a curved curtain which opens to allow the water to escape into the river. The gap is “managed” by the keeper and at the right time, the gate will be fully opened to allow boats to access the Thames.
The first time we cruised from Limehouse heading upstream was eventful. The lock gate was under repair and could not be opened slowly. It was “all or nothing”, so as the gate was opened, Kailani tipped forward and resembled a downhill sledge entering the Thames. We remember it well!!
Etiquette at locks is an important matter! It doesn’t mean “first come, first served”, as with other matters. On reaching a lock, if your end can be opened without filling or emptying the lock, you have the right to enter and proceed to fill/empty it. But if another craft is approaching from the opposite direction and the water is in their favour, you must wait for them to come through the lock first. Then it’s your turn to proceed. In short, this method saves water – usually a precious commodity on the canals. A major way to save water is to share the lock. Not easy when you have a wide beam boat, but on the wider canals, two narrowboats can share a lock
On rivers a number of boats can be waiting to enter a lock. The lockkeepers may decide to fill the lock in a particular order, so you must await their signal to enter. If a boat attempts to enter a lock before being asked in, “beware the wrath of the keeper.”
On Kailani we are always grateful when guests are willing to help with locks. We believe it is part of the waterways experience and guests have said they are pleased they were able to get involved. We always show guests how to safely operate locks, paddles and use their windlass and most pick up the skill quickly. Unfortunately, some are none the wiser after a day operating the locks, so we tactically suggest they take a rest on the bow deck and watch others do the work! Thanks for trying, but we don’t want you to get hurt!
We fondly recall Daisy, 9-year old daughter of a couple who would not allow her dad to help with the locks. She was determined to lock-wheel at every lock on the family’s cruise with us. She also slept well.
We cannot write about locks without mentioning the wonderful team of unpaid volunteers, either on CRT or Environment Agency waterways, who attend locks and give their time and experience to help boaters through the process of locking through. Many are present or past boaters, or even willing local people who give a day every week or occasional help – many thanks to you all; to us you’re all winners!
To all guests who help us, we ask just one thing .…… “Whatever you do, don’t lose your windlass!!”