How locks work
Water doesn't go up and down hills very well... well, not so a boat could sail on it, but canals do up and down hills, so how do they manage it? In some places, special machines were build to move boats up and down, but most of the time the canal builders used something called 'locks'.
Although locks can be quite scary places; lots of water, weeds and funny smells, they're really quite simple. A few pictures will help me explain how they work.
I want to go down the lock. The lock is full of water and both gates are closed.
Lets' open the top gate and let the boat sail in...
Those gates have to be really strong because there's a lot of water pressure behind each one. They're usually made of oak - a strong heavy wood. Sometimes the long bars across the top - the balance beams - are wooden; sometimes they're made of metal.
If you look at the next picture, you can see we've closed the top gate, and if you look closely, we've opened a gap in the bottom gate to let the water out. All the lock gates have things called 'paddles'. These are wound up and down with a special handle called a windlass. You might see my crew carrying them - they look like big crank handles.
Anyway, once that paddle is open (making sure that the top ones are closed, otherwise all the water runs out of the canal), the water level in the lock will drop to the same as the level of the lower part of the canal.
There. We're at the right level. We can close the paddles now and...
...open the gate and out we go.
We must remember to close the gates before we go...
...,making sure that we've closed all the paddles.
There. that wasn't too difficult was it?
Putting all that lot together, David has made a little animation that shows it all happening. It doesn't happen this quickly in real life though... he's speeded things up! It can take 15 minutes to go up or down a lock, so you'd better not be in a hurry.
If you look carefully, you might see that I get right to the front of the lock. This is to avoid the thing that sticks out at the back that the gate rests on. This is called the 'cill'. If I was over the cill when the water started pouring out of the lock, my stern could get caught and I'd end up in a right old mess with my nose in the water and my bum on the cill! This could also be dangerous, so I have to keep a careful eye on my crew!
Remember. Locks are deep and may have hidden obstructions under water. It's never safe to play near locks. Accidents can happen and I'd hate to hear of any of my friends getting themselves injured or worse. Take the advice of my crew: don't run on lock sides and don't play on the gates.
Enjoy the canals, but treat them with respect.