Why do locks have cills?

[Chris J W]

Ok, maybe it is a stupid question - but why do locks have cills? Obviously our Industrial Revolution Engineers decided they had to be there, but, well, why? Can't for the life of me figure that bit out.

[minerva]

To make boaters look stupid?

[carlt]

To provide a foundation to hang the gates on.

[Chris J W]

To provide a foundation to hang the gates on.

 

Ok. So why INSIDE the lock where they can cause problems and not outside?

[denboy]

Ok. So why INSIDE the lock where they can cause problems and not outside?

stops the water pressure on the high side of the lock from pushing the gates in the wrong direction ie its basicly a door stop and it prevents the errosion of the canal bottom under the gates

Edited July 2, 2007 by denis boyle

[Yamanx]

It probably has something to do with the construction methods at the time. On the Huddersfield Narrow theres a brand new lock made from re-enforced concrete, using modern construction methods. I'm reasonably certain it doesnt have a cill.

 

I have noticed that some cills are retractable and have lifting eyes fitted. They are dropped into slots. I cannot guess why this is so?

[carlt]

I have noticed that some cills are retractable and have lifting eyes fitted. They are dropped into slots. I cannot guess why this is so?

This is so that the lumps that get the wear, from water erosion and boats bashing into them, can be craned out and repaired/replaced.

[bristol & argo]

It probably has something to do with the construction methods at the time. On the Huddersfield Narrow theres a brand new lock made from re-enforced concrete, using modern construction methods. I'm reasonably certain it doesnt have a cill.

 

I have noticed that some cills are retractable and have lifting eyes fitted. They are dropped into slots. I cannot guess why this is so?

 

Do you step down out of your front door? then you have a cill. It's just the same as the lock, think of the top gates as your front door.

Depending on the construction materials, and the nature of the ground you could get a very short cill, in fact only just enough for the bottom of the gates to seal against.

You wont even see the cill on many shallow locks - which is where the problem comes when the unwary come to a deeper lock.

 

Was the retractable cill with lifting eyes made of timber? if so it's not the cill, it's a timber bulk to act as a fender, and stop 40 tons of narrowboat from cracking the real cill if it hit it at full speed!

 

Simon.

[fender]

Do you step down out of your front door? then you have a cill. It's just the same as the lock, think of the top gates as your front door.

Depending on the construction materials, and the nature of the ground you could get a very short cill, in fact only just enough for the bottom of the gates to seal against.

You wont even see the cill on many shallow locks - which is where the problem comes when the unwary come to a deeper lock.

 

Was the retractable cill with lifting eyes made of timber? if so it's not the cill, it's a timber bulk to act as a fender, and stop 40 tons of narrowboat from cracking the real cill if it hit it at full speed!

 

Simon.

 

As Simon says they are there to stop boats cracking the cill.

 

I dont think there's any way a lock can work without a cill. Its not just the top gates that have cills, but the bottom gates too.

[andywatson]

Ok, maybe it is a stupid question - but why do locks have cills? Obviously our Industrial Revolution Engineers decided they had to be there, but, well, why? Can't for the life of me figure that bit out.

 

My 2 pennorth as an engineer not canal expert is as follows........

 

I see no reaon why a lock could not be built with the cill on the outside of the gate and still work. However:

A-more ground would need to be excavated and then lined.

B-the top gates would need to be as deep as the lower level/gates.

C-the lock would be slightly weaker unless stregthened to take account of the 2 above

D-the chamber between the larger upper lock gates and exterior cill would probably be more sensitive to silting up and debris collection

 

Since the first 3 items above have (increased ) cost implications I am not surprised that locks are built the way they are. The canals were built at minumum cost for professional use use not by us lot.

Edited July 2, 2007 by andywatson

[sleeper]

Some cills are so low down you never see them?

[carlt]

Some cills are so low down you never see them?

Eh? You don't see the lower cills because they're at least 3' below water all the time and you always see the upper cills when the lock is empty, except, maybe, at stop locks with very little drop.

[fender]

Eh? You don't see the lower cills because they're at least 3' below water all the time and you always see the upper cills when the lock is empty, except, maybe, at stop locks with very little drop.

 

Some you can see - p'haps when the canal is dewatered. Others regularly - like at Thames Lock Brentford when the tide is out the lower cills are exposed.

[Dave-Shrop]

The cill is the change in level of the canal, ie the bottom of the canal is lower on the down side than above and it has to be at the gate.

[carlt]

Some you can see - p'haps when the canal is dewatered. Others regularly - like at Thames Lock Brentford when the tide is out the lower cills are exposed.

Yes but if you're going downhill and you want to exit a lock and you can see the lower cill, unless the water is crystal clear (unlikely after churning it about emptying the lock), you've got a problem.

[fender]

Yes but if you're going downhill and you want to exit a lock and you can see the lower cill, unless the water is crystal clear (unlikely after churning it about emptying the lock), you've got a problem.

 

All cills cause problems when the circumstances are right - or wrong!

[Chris J W]

Blimey - ever get the feeling you really shouldn't have asked a question?

 

 

Thanks for all the answers .. but getting the feeling that this is a real "banter" conversation where someone could start scribbling diagrams on backs of beer mats ...

 

 

So maybe I should rephrase the question - Do locks HAVE to have cills?

 

 

[edit for typos]

Edited July 2, 2007 by Chris J W

[KenK]

Blimey - ever get the feeling you really shouldn't have asked a question?

So maybe I should rephrase the question - Do locks HAVE to have cills?

[edit for typos]

 

I'd agree why did you ask the question, what's the point. The system is over 200 years old, there are many different types of lock but they are all still functional, many after decades of neglect. I'm sure with modern engineering methods and techniques a better method could be devised but why? Most of us are romantics otherwise we wouldn't spend a small fortune trying relive the past. The waterways network is all about, for me, stepping back in time to a slower pace of life, relaxing, etc. If the worst I have to worry about is keeping clear of the cill and of course how far to the next pub, then that's just fine.

 

Don't question it just enjoy it and try to preserve it.

 

 

Ken

[Chris J W]

I'd agree why did you ask the question, what's the point. The system is over 200 years old, there are many different types of lock but they are all still functional, many after decades of neglect. I'm sure with modern engineering methods and techniques a better method could be devised but why? Most of us are romantics otherwise we wouldn't spend a small fortune trying relive the past. The waterways network is all about, for me, stepping back in time to a slower pace of life, relaxing, etc. If the worst I have to worry about is keeping clear of the cill and of course how far to the next pub, then that's just fine.

 

Don't question it just enjoy it and try to preserve it.

 

 

Ken

 

Erm - I asked because I've an enquiring mind that accepts that engineering techniques have moved on over the years, but with all real respect to the folks that sweated blood to make these water ways I'm still not clear about "why" the cills are there, even understanding the 'foundation' aspect.

[KenK]

Erm - I asked because I've an enquiring mind that accepts that engineering techniques have moved on over the years, but with all real respect to the folks that sweated blood to make these water ways I'm still not clear about "why" the cills are there, even understanding the 'foundation' aspect.

 

OK. I am an engineer not however a civil engineer. A door because that's what a lock gate is, needs to be sealed, against in the case of a house against the ingress of wind and rain. A lock gate needs to be sealed against the ingress of water. If the bottom of the gate does not rest on something soild originally stone latterly concrete then water would wash away the bed of the canal / river and the lock would leak. Eventually the lock would cease to function because the amount of water entering the lock even with the gates closed would be greater than the paddles at the other end could remove. Or both sets of gates would leak and the pound would empty. Why build the cill inside as well as outside the lock, I suspect because it looked to the original designers like the best method and it helps to protect the gates from impact by the boats. Originally the boat was powered by the horse but stopped by ropes, get it wrong and you crashed into the lock gate. Don't forget most of the early canal designers / builders were not engineers, they were self taught, they made it up as they went along. If it worked they used it if not they tried again, I guess the cill worked.

 

That's my explanation, might be right possibly wrong. There may be a historian who has a better explanation if so I for one would be interested.

 

 

Ken

[gaggle]

boaters go bashing into whatever is in front of them , so the cill is a buffer zone , boats can bash it and if they bash it hard enough and knock out some stonework the water above will not cascade through the gap as the cill protrudes out from the vertical line of the gate.

[Alistair]

Lock gates have cills so the gates don't leak (or burst) at the bottom.

 

Just as the side of a gate must push against something strong when the gate is closed and under pressure (differing water levels = pressure), so must the bottom. So you make a thing called a cill for the water to push the bottom of the gate against.

 

Empty the lock (or the next pound), take the cill away and the bottom of the gate has nothing to push against.

But you never see the cill when you empty the lock so it will never have to hold all the water back so it'll be fine without it.

 

Sure. When you're cruising normally, you only see the cill for the top gate in a deep lock. Indeed that's the only time you worry about the cill. Take that cill away and the top gate bursts.

 

Now try pumping out a lock, or dewatering a pound, without cills for top and bottom gates. And if you get a leak in your canal and the cills don't hold at the first lock up you've got another leak.

[denboy]

boaters go bashing into whatever is in front of them , so the cill is a buffer zone , boats can bash it and if they bash it hard enough and knock out some stonework the water above will not cascade through the gap as the cill protrudes out from the vertical line of the gate.

 

rochdale canal 2 years ago a boat hit the cill so hard it knocked the cil out emptied the pound i was stuck for 3 days while BW put it back they were not impressed if they had of caught the boater they would have hung him

[gaggle]

i have only seen flat stones with a small seeling strip of wood that meets the bottom of the gate , never seen a cill "ledge "behind the gate for it to push against and seal it.

 

dennis i can well believe it has happened in the past and without the cills it would no doubt happen on a regular basis.

[GRPCruiserman]

Tarleton Sea lock has no cill, the canal gradually gets as deep as the river bottom (or at least the river side of the lock), and the lock gates top and bottom are the same depth, so you can't get stuck on the cill. You could get caght on the gate sross braces though!!

 

Onthe river side of the lock there is a kind of cill, but the tide would have to be very low for you to hit it, and I've seen deep draft boats get in much later than you'd expect before now, so it's pretty low down. You can see it when the tide is out.