Wednesday, 15 June 2011

Particular Intricacies Of Locks For Those Who Are Unfamiliar With The Process

Canals and locks are a mystery to some people. This doesn’t particularly surprise me, since before last year they didn’t really exist in my world – I would have been hard pressed to remember what a lock was called, let alone explain how it worked. But there are a growing number of friends, guests, passersby etc who ask us to describe what’s going on and how it happens. So here goes...it might be a very long-winded way to explain an incredibly simple process, but I think it covers most things.

The canal system in the UK is a mish-mash of interconnected rivers and passages, developed over a long time (it’s still going on today, although it’s mostly restoration and not creation). I don’t have the space to go into the entire history of locks but there are heaps of websites and books devoted to the topic – if you’re interested in a brief overview that isn’t country-specific, try Wikipedia’s entry.

Our country isn’t flat. There are hills and undulations and valleys, and there had to be some way of overcoming this if we were ever to use boats as long-distance transport (obviously these were the days before trains, planes and automobiles; cargo businesses on canals and rivers are now only a tiny fraction of what they once were). So locks were used, and standard sizes put into place by Brindley. Lock sizes vary from canal to canal, with big Thames locks able to accommodate lots of boats at once and “narrow locks”, which are about 7’ by 70’, only generally meant for one narrowboat. The locks Tranquil Rose can go through have to be over 12’ wide, so we can’t go further north than Warwick as they tend to narrow after this.

The basic idea of a lock is that a vessel can be lifted up from one level of water to the next, so the whole waterway system is a series of steps. There are various ways other than locks to do this – for example the Anderton Boat Lift or the Falkirk Wheel - but these are few and far between.

So, how do we work them? When you’re approaching a lock in your boat, it’s a good idea if you can spare someone to jump off (onto the bank, obviously) and run ahead to set it. Setting it means making sure the level of water in the lock is the same as the level at which your boat is sitting, so that the gates can open and the boat can enter. To do this you use a windlass, which is a right-angled “key” which fits onto the spindle attached to a paddle built into the gate. When you wind the spindle round with your windlass, it raises or lowers the paddle, either letting water in or keeping it out.

With me so far?

When you’ve equalled out the levels of the water, it should be easy enough to open both of the gates. It’s nice to have a person on each side so you don’t need to run down to the end gates and over the lock to open the second one yourself – although on the narrow locks, given a bit of bravery, you can jump the three or so feet from the gate you’ve just opened to the edge of the one on the opposite side, negating the need for all the running about.

Then the boat can get into the lock, and you shut the gates behind it, remembering to wind the paddles back down. If you leave the paddles up, then start letting water in the other end, it’ll go straight through the lock, the boat’ll go nowhere, and you might flood the pound – stretch of water between locks – below. There’s a cill under the water at one end (it means sill. I have no idea why they spell it cill. But they do) which is the bottom of the higher bit of canal, so if you’re going downhill you need to make sure the boat has the space to be away from that; if the water is let out and the stern of the boat gets stuck on the cill while the bow is still going down...well, it’s not good. Picture it.

So the boat’s in the lock - let’s say at the bottom, so you’re going uphill. The person with the windlass, after making sure the paddles in the bottom gates are now closed, goes to raise the paddles in the top gates, letting water in so that the level in the lock gets high enough to be equal to the level in the pound above. Depending on the depth of the lock and the size of the boat, this can be done with varying amounts of speed. Top gates can have ground paddles and/or gate paddles. Ground paddles are channels from the pound into the lock going through the brickwork of the sides, so the water flows underneath where you’re standing – this is a safer/slower method of getting water in, and should always be used first. Gate paddles are, as it sounds, paddles built into the gate, so if you’ve got people sitting in the front of your boat and you open the paddles while they’re still above the water level, those people have got a bit of a soaking in store. Generally you open the ground paddles and wait until the water covers the gate ones, then you can open them with minimum splashing!

When the water has risen enough to be level, you open the top gates, allowing your boat to exit the lock, and away you go. On most canals the etiquette is to wind the paddles back down and close the gates after you, although there are a couple of exceptions – the Wey Navigation in Surrey, for example, is one waterway where you leave open whichever gates you’ve exited (although still winding the paddles down), ready for the next boat to come in the opposite direction. Obviously if there’s a boat on the horizon heading towards you on other canals, it’s a bit mean to close the gates right in front of them so in that case it’s fine to leave them open!
The easiest way to remember the tos and fros of it is just to do it, but it does help to have a basic understanding. So if you’re planning on boating in the near future, I hope it’s been of some use. If it hasn’t, don’t worry, I’ll go back to writing poems in a day or two.

1 comment: