Simple question relavent to all.

[SoJo]

Why do narrow locks have a single gate at the top and two gates at the bottom?Got to be a simple answer.

[BlueStringPudding]

Why do narrow locks have a single gate at the top and two gates at the bottom?Got to be a simple answer.

 

Excellent question which I never thought to ask.

 

Reveal wise sages!

[Tusses]

Excellent question which I never thought to ask.

 

Reveal wise sages!

 

 

I would GUESS ! that once you are in the lock - the split gate takes up less(half) room as it opens, leaving room for a longer boat - or shorter (cheaper) lock

[BigRoj]

This is a guess, but I would imagine that when the lock is full, and the single gate is opened, all the water of the previous pound is up against the end gates. If it was a single, there would be a lot of strain/pressure on that gate. However, a double gate is wedged in a V shape, and is thus more able to accept this pressure, and make it more water-tight than a single gate would. The only time all the previous pounds water pressure is on the single gate is when a boat is exiting the bottom gates. (which is why you should keep the gates closed to conserve water)

 

I suspect also that double gates will be used where there is a long pound and a deep lock.

 

Possibly.

[Bones]

This is a guess, but I would imagine that when the lock is full, and the single gate is opened, all the water of the previous pound is up against the end gates. If it was a single, there would be a lot of strain/pressure on that gate. However, a double gate is wedged in a V shape, and is thus more able to accept this pressure, and make it more water-tight than a single gate would. The only time all the previous pounds water pressure is on the single gate is when a boat is exiting the bottom gates. (which is why you should keep the gates closed to conserve water)

 

I suspect also that double gates will be used where there is a long pound and a deep lock.

 

Possibly.

 

impossible - somerton deep lock is single gates both sides. Sugg has just pointed out that the doubles are north of banbury and has an eleborate theory he will have to write himself, but it sounds viable. something to do with length of the boat, horse drawn boats and the co-op.

[BigRoj]

As I said, it was just a guess. After all, I am just a mere Mechanical Engineer, what would I know?

[Moley]

Sugg has just pointed out that the doubles are north of Banbury

 

Birmingham's north of Banbury, and there are single gates top and bottom on one stretch around the BCN, Fazeley side I think, but don't hold me to that one.

[fender]

The Macclesfield has double gates top and bottom - and its a narrow canal too!

[giveitsomeoil]

I would say; that when the top gate (single) is closed and the lock is empty the seal for the single gate is supported by 75ft of high ground ie. the lock side. If this were the case at the tail end of the lock, the sealing wall would have no support. By having a pair of V gates wedging together the lload is spread outwards across both walls evenly. I know exceptions exist in short pounds or possibly areas of different gound make up.

[SoJo]

Thats my favorite so far.

[Scotty]

impossible - somerton deep lock is single gates both sides. Sugg has just pointed out that the doubles are north of banbury and has an eleborate theory he will have to write himself, but it sounds viable. something to do with length of the boat, horse drawn boats and the co-op.

lol I was just going to say that as I did Somerton Deep this morning,

it's 12ft deep and I can confirm has single gates top and bottom, a lovely cottage too

 

Birmingham's north of Banbury, and there are single gates top and bottom on one stretch around the BCN, Fazeley side I think, but don't hold me to that one.

I think Bones was refering to the Oxford, where they are single gates south of Banbury

[Keeping Up]

I've often heard it stated that they used a pair of gates at the bottom so they could have a shorter lock and save some money (not having to make the lock long enough to leave room to open the gate when there's a boat inside) but then that doesn't explain why some locks have single gates at both ends.

[carlt]

I've often heard it stated that they used a pair of gates at the bottom so they could have a shorter lock and save some money (not having to make the lock long enough to leave room to open the gate when there's a boat inside) but then that doesn't explain why some locks have single gates at both ends.

More affluent canal companies?

[adam1uk]

My understanding is that they had two gates at the bottom because they're lighter than one big gate and thus easier to install and operate. Weight isn't a problem at the top end, as the gate is usually quite short.

 

However, it was cheaper to make one single gate than a pair, so when the canal companies needed to save money they went for that option. I'm pretty sure the explanation in the Pearson's guide to the Oxford canal says the single gates south of Banbury were for financial reasons.

[bargeeboy]

Why do narrow locks have a single gate at the top and two gates at the bottom?Got to be a simple answer.

 

I am now looking for the relevant explanation as recorded by Henry de Salis in Bradshow's Canals and Navigable River 1904./

 

I will post after I hand over a new Narrowcraft Classic narrowboat to its new owners. This can now be seen on our new office/craning cam from our website. Live craning next Saturday when 2 more arrive.

 

I hope your boat is still up to expectations Sojo. It must be over a year since you took delivery

Edited March 29, 2008 by bargeeboy

[Hairy-Neil]

Birmingham's north of Banbury, and there are single gates top and bottom on one stretch around the BCN, Fazeley side I think, but don't hold me to that one.

 

The Wolverhampton '21' has both types on the same flight......

[fender]

This question has come up in the past, there was a feature in WW some years ago. No answers can be found apparently, it just seems to be the canal companies expectations and whims, and what the canal builders could offer.

 

Single gates generally cost more because extra land and bricks is required for the lock chamber, whilst double gates dont require longer lock chambers thus saving on potential land costs. The ironic thing is double gates usually cost more than single gates to make! And one more thing, transporting of single gates were more difficult and costly than those for double gates

 

We like to think that the early canal builders had a rationale but if you look closely you'll find that much of it was just decided on the spot, not planned beforehand.

 

Ends

[SoJo]

Boat's still great Bargeeboy,keep up the good work!

[Dominic M]

Why do narrow locks have a single gate at the top and two gates at the bottom?Got to be a simple answer.

Reasons of economy - it was cheaper to have a single gate.

 

The Oxford Canal south of Banbury has single gates at both ends also for reasons of economy. The Oxford Canal Co reached Banbury from its junction with the Coventry Canal in 1778. At this point the funds had dried up, and the canal did not reach Oxford and the Thames for another 12 years. The Banbury - Oxford section was built as cheaply as possible, hence the single bottom gates, and also the large number of the lift bridges on that stretch, which were far cheaper to build than brick ones, although they slowed the progress of boats significantly.

[magnetman]

I noticed the other day that the stop lock at Hawkesbury Hairpin has single gates both ends. Being a shallow lock there is no exposed cill - if there had been my boat would not have passed the lock, going down, as the single bottom gate needs a lot more space to open. I imagine original design was dictated by the engineer in charge and opinions do tend to vary :banghead:I noticed the other day that the stop lock at Hawkesbury Hairpin has single gates both ends. Being a shallow lock there is no exposed cill - if there had been my boat would not have passed the lock, going down, as the single bottom gate needs a lot more space to open. I imagine original design was dictated by the engineer in charge and opinions do tend to vary

[fender]

Hawkesbury lock has small cills. I have photos from a stoppage when it was drained for works.

 

The other thing is there was no lock was not at Hawkesbury originally. It cannot be said that it was the designers who thought of the single gates here.

 

It was built when the Oxford and Coventry canals agreed to move their junction from Longford to Hawkesbury.

 

PS Autherley, Marston and Hawkesbury all featured single gates top and bottom

Edited March 30, 2008 by fender

[RobinR]

Excellent question which I never thought to ask.

 

Reveal wise sages!

 

Probably based on the informed decision of the design engineer or the then current policy of his (her) employer at the time and to address specific percieved construction challenges at the respective locations. These will have changed with time and experience dependant on current operating practice and available funds. This is the normal development process which continues to the present day! May be archive records, where they still exist, would be the closest to answering the question.

[Proper Job]

I noticed the other day that the stop lock at Hawkesbury Hairpin has single gates both ends. Being a shallow lock there is no exposed cill - if there had been my boat would not have passed the lock, going down, as the single bottom gate needs a lot more space to open. I imagine original design was dictated by the engineer in charge and opinions do tend to vary :banghead:I noticed the other day that the stop lock at Hawkesbury Hairpin has single gates both ends. Being a shallow lock there is no exposed cill - if there had been my boat would not have passed the lock, going down, as the single bottom gate needs a lot more space to open. I imagine original design was dictated by the engineer in charge and opinions do tend to vary

I see you still havn't shaken off that stutter yet

[hnb2907]

The Macclesfield has double gates top and bottom - and its a narrow canal too!

...except the stop lock at Hall Green, which has 2 top gates and single bottom one

[Keeping Up]

I see you still havn't shaken off that stutter yet

Maybe that's how you get double gates ?