Canal Lock Gates

[Mimi]

Daft question alert! I know there is probably a simple reason but I cant work it out. Can anyone tell me why most canal locks have one gate at one end and two at the other? (obviously two each end if its a double).

 

[Paul C]

The double gate are taller because they've got to go down to the depth of the lower pound, whereas the single gate only has to go down to the depth of the upper pound. Obviously they both have (approx) the same level at the top of them. So on many canals they're double so they're not too heavy. There's narrow canal locks with singles at both ends (eg loads in Birmingham) and ones with doubles at both ends. (And of course broad canals, rivers etc where they're both double).

Edited March 15, 2015 by Paul C

[Rich]

Daft question alert! I know there is probably a simple reason but I cant work it out. Can anyone tell me why most canal locks have one gate at one end and two at the other? (obviously two each end if its a double).

 

Possibly because the bottom gates open into the lock and therefore being narrower will occupy less of the lock length meaning that you get longer boats in shorter locks, or summat.

[Flyboy]

Another good reason to have double bottom gates on a narrow lock is that the lock chamber can be shorter. This saved on building costs, reduced the amount of water used so emptying & filling would be slightly quicker,

[Guest]

Daft question alert! I know there is probably a simple reason but I cant work it out. Can anyone tell me why most canal locks have one gate at one end and two at the other? (obviously two each end if its a double).

 

 

Have a read of this thread I started on the exact same point (five years ago now...how time flies)

 

http://www.canalworld.net/forums/index.php?showtopic=28344&hl=gates

Edited March 15, 2015 by MJG

[OldGoat]

Firstly it's not all narrow canals that have a single top gate (but most do). Some shallow locks have single gates at the top and bottom -e.g. those below Banbury on the Oxford

Secondly having double bottom gates is not so much a possible saving in lock chamber length but more of:-

• the extra weight and cost of heavier timbers in a single gate
• a double gate with a mitre is more efficient to seal than a single gate with a butt seal

A good example of a heavy (!) and cumbersome gate is Somerton deep on the Oxford.

[Mac of Cygnet]

Firstly it's not all narrow canals that have a single top gate (but most do). Some shallow locks have single gates at the top and bottom -e.g. those below Banbury on the Oxford

 

 

And some rather deep ones too! e.g. the Diggle flight on the HNC.

[OldGoat]

 

And some rather deep ones too! e.g. the Diggle flight on the HNC.

 

Yes - but I've never been able to go there - probably need a passport. (I'm darn sarf...)

[Theo]

And Bosley has double gates at the top. It makes for very light locking!

 

N

[Idunhoe]

And Bosley has double gates at the top. It makes for very light locking!

 

N

And quite a lot of walking if you are single handed

[furnessvale]

And quite a lot of walking if you are single handed

Use a "Bosley" shaft. Long but light enough to carry with you to open or close offside gates as required.

 

George ex nb Alton retired

[MtB]

Or just step across the gap

[Scholar Gypsy]

Firstly it's not all narrow canals that have a single top gate (but most do). Some shallow locks have single gates at the top and bottom -e.g. those below Banbury on the Oxford

Secondly having double bottom gates is not so much a possible saving in lock chamber length but more of:-

• the extra weight and cost of heavier timbers in a single gate
• a double gate with a mitre is more efficient to seal than a single gate with a butt seal

A good example of a heavy (!) and cumbersome gate is Somerton deep on the Oxford.

I am not sure I would buy the point about sealing. A well installed & maintained single gate can be completely watertight, while mitre gates always seem to leak a bit (and sometimes a lot!) Edited March 15, 2015 by Scholar Gypsy

[MtB]

Firstly it's not all narrow canals that have a single top gate (but most do). Some shallow locks have single gates at the top and bottom -e.g. those below Banbury on the Oxford

 

I've just transited Pigeon's Lock with a single gate at each end and I wouldn't describe it as 'shallow'!

[OldGoat]

I am not sure I would buy the point about sealing. A well installed & maintained single gate can be completely watertight, while mitre gates always seem to leak a bit (and sometimes a lot!)

 

 

Damn......

 

Oh, umm - how about this then:-

It's easier to get a good seal for a mitred pair on the mitre and the heel on the landward side - because the mitre is arranged such that the closed gates also exert a force against the heel and whatever the curbed-socket-bit is called in the loch wall.

 

I submit m'lud that the single gate doesn't do that as well??

[furnessvale]

Or just step across the gap

There aren't many prepared to step across the gap on Bosley top gates.

 

I've never done it and I've never seen it done.

 

I have however routinely walked over the CLOSED gates when younger, but getting closer to 70 by the day, I now wait for the boat to rise and use the top plank or roof.

 

George ex nb Alton retired

[OldGoat]

 

I've just transited Pigeon's Lock with a single gate at each end and I wouldn't describe it as 'shallow'!

Well 'tis not deep either - what's the fall? Oh well there must be another reason 'cos there are more than one deep-ish locks on t'Oxford with single bottom gates. Preps its about the wood

(You just can't get the wood, Minnie)

[Guest]

There aren't many prepared to step across the gap on Bosley top gates.

 

I've never done it and I've never seen it done.

 

I have however routinely walked over the CLOSED gates when younger, but getting closer to 70 by the day, I now wait for the boat to rise and use the top plank or roof.

 

George ex nb Alton retired

I've said this before on here and got stick for it but I have never stepped across a gap on any locks. I just have never felt in that much of hurry, the stick I got was around 'did I not want to take pride in moving through a lock efficiently as possible?'. Well back in the working boat days when there was a need for 'efficiency' I probably wouldn't have got a job, fair enough.

 

But nowadays I have never felt the need to take what I consider an uneeded risk, of falling in spectacularly.

[magpie patrick]

Single top gates were the innovation, until narrow locks came along then almost all locks had double gates at both ends.

 

Narrow locks are small enough to make a single gate practical, in terms of being light enough to open and close easily, and also take the load. Bear in mind that mitre gates transmit the load into the lock wall at an angle, whereas single leaf transmit the load down the lock wall. Also, the mid point of a gate is reliant upon the strength of the gate to take the load, with single leaf gates this means stronger gates are needed. But again narrow locks are small, most broad lock gates, despite each being one of a pair, are bigger than single leaf narrow lock gates.

 

But, at the bottom, the gates open into the lock (and the load is greater). Opening into the lock adds length that the boat can't occupy, which uses water. But as I say, it was the single gate that was the innovation

 

Some narrow locks have single bottom gates: the main reasons are ran out of money and it was presumably cheaper (southern Stratford and South of Banbury on the Oxford), speed of operation (BCN) and putting everything on the non-towpath side (Diggle locks HNC).

[Scholar Gypsy]

 

 

Damn......

 

Oh, umm - how about this then:-

It's easier to get a good seal for a mitred pair on the mitre and the heel on the landward side - because the mitre is arranged such that the closed gates also exert a force against the heel and whatever the curbed-socket-bit is called in the loch wall.

 

I submit m'lud that the single gate doesn't do that as well??

 

I don't think that is correct. The plane of the seal at the heel post is parallel to the gate: the pin at the foot of the gate and the collar etc at the top of the gate are what transmit the horizontal thrust from the lock sides on the gate (in the plane of the gate). There's another thread about the forces on lock gates that I will try to find sometime ..

 

S

[Tacet]

How many locks have a pair of top gates and single gate at the tail end?

[Scholar Gypsy]

How many locks have a pair of top gates and single gate at the tail end?

 

Most of the locks on the Nene; and some on the Bedford Ouse (eg St Neots, St Ives)?

[magpie patrick]

How many locks have a pair of top gates and single gate at the tail end?

 

If you mean canal locks, 1, Hall Green, but I like Scholar Gypsy's answer because I hadn't thought of it!

[Pluto]

With a single gate, the all the force created by water pressure is in line with the lock side, while with a mitre gate the force is divided, partly in line with the lock and partly at right angles and thus pushing into the lock sides. As a result, single-gated locks tend to have longer lower ends below the bottom gate as a way of making them sufficiently strong to withstand the pressure. Mitre gated locks could be shorter here, but needed more strengthening of the walls at the quoin to withstand the outward thrust.

[Mac of Cygnet]

 

Most of the locks on the Nene; and some on the Bedford Ouse (eg St Neots, St Ives)?

 

Is a guillotine a gate? Just being picky but to me a gate has to swing.