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Fierce gate paddles...


magpie patrick

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Looks to be pretty standard exit speed for fully open Du Midi locks bottom paddles although that's at least a 2rise' that was my point in a earlier post/thread about a narrow boat not being an ideal french canal boat

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The riser locks on the Canal du Midi were designed to be operated by draining the chambers completely when descending. When the rise was three chambers or more, the centre chambers were built shallower than the top and bottom chambers by the navigable depth of the canal. This has the possible advantage of ensuring that no rubbish collects in the central chambers which can damage the cill or mitre when the gates close fully under water pressure. In England, riser locks were designed such that the chambers always kept a navigable depth when empty, with the fall of each chamber being the same. This does mean that rubbish can be retained within the chamber and this can cause damage to the gates if caught on the cill.

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To add to Pluto's comment, this means that, when ascending, a boat doesn't come anywhere near the gate paddles filling the lock, except in the top lock which they are very careful with! 

 

That said, when filling Fonserrannes these last few days, only the chamber ahead of the boat has been drained, but then, there have been boats following each other up the staircase.

 

The picture was taken with a boat descending. 

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At least with most locks the lock keepers are employed & are usually confined to a small area living in the lock cottages the ones Ive dealt with are well clued up on the foibles of their lock/s & can very quickly suss out the boaters capabilities & react accordingly

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On 28/10/2018 at 12:27, Pluto said:

The riser locks on the Canal du Midi were designed to be operated by draining the chambers completely when descending. When the rise was three chambers or more, the centre chambers were built shallower than the top and bottom chambers by the navigable depth of the canal. This has the possible advantage of ensuring that no rubbish collects in the central chambers which can damage the cill or mitre when the gates close fully under water pressure. In England, riser locks were designed such that the chambers always kept a navigable depth when empty, with the fall of each chamber being the same. This does mean that rubbish can be retained within the chamber and this can cause damage to the gates if caught on the cill.

Having looked at these locks a lot over the last four days I'm not convinced this is true at Fonserrannes though. At first I though the top chamber was deeper, as it has more steps at the bottom end then the rest, but realised it has nearly four feet of freeboard when full, whereas the other locks are operated with less than a foot of freeboard. I also counted the footholds/handholds on the  lock ladders last night when the whole flight was drained (they seem to drain it every night) and with all the chambers drained the top 4 chambers all had 15 hand/footholds that were wet - there were a few more dry ones in the top chamber because of the freeboard.

 

Of course it is possible they all originally operated with a lot of freeboard - the top chamber is deeper than the others, but it doesn't currently lift more than the others. 

 

The fifth and sixth chambers are affected by the changes made in the mid-19th century, which leave the sixth chamber with a fall of (I guess) about 3 feet and means the fifth chamber doesn't fully drain. 

 

I haven't actually made it out  of Beziers yet...

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20181028_174733.jpg

Edited by magpie patrick
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1 hour ago, magpie patrick said:

Having looked at these locks a lot over the last four days I'm not convinced this is true at Fonserrannes though. At first I though the top chamber was deeper, as it has more steps at the bottom end then the rest, but realised it has nearly four feet of freeboard when full, whereas the other locks are operated with less than a foot of freeboard. I also counted the footholds/handholds on the  lock ladders last night when the whole flight was drained (they seem to drain it every night) and with all the chambers drained the top 4 chambers all had 15 hand/footholds that were wet - there were a few more dry ones in the top chamber because of the freeboard.

 

Of course it is possible they all originally operated with a lot of freeboard - the top chamber is deeper than the others, but it doesn't currently lift more than the others. 

 

The fifth and sixth chambers are affected by the changes made in the mid-19th century, which leave the sixth chamber with a fall of (I guess) about 3 feet and means the fifth chamber doesn't fully drain. 

 

I haven't actually made it out  of Beziers yet...

 

I am only going off the description in Maillard's book on canal building where he gives the two variations, depending on whether the chamber is drained or continues to have navigable water depth when emptied - what's the French for a tape measure, then you can buy one and get more exact details. The variation in freeboard you mention does suggest that there may have been some alterations when the aqueduct was built. There also seem to have been problems with leakage on the southern end of the canal in the late 18th century, so water levels could have been altered. They did not have a suitable source for clay for puddle and seem to have used a particular type of earth mixed with small stones, which was not that effective. The development of puddle is something I keep meaning to do a bit of research on. Hopefully they will have some information in the Canal du Midi Archive in Toulouse.

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20 minutes ago, Pluto said:

I am only going off the description in Maillard's book on canal building ....

Which is on my wish list once your translation hits the bookshops...

 

I've been so fascinated with the set up that I've only so far looked at the canal between L'ecluse Bezier (the western end of the Orb aqueduct diversion) and the top of the Staircase, about four miles of canal and river if you include both routes. It's intriguing watching boats go up and down and, on Saturday, boats were following each other up and down which probably means the regime is varied from that of a single boat passage. In any event, there is a difference between how the locks were intended to be worked when they were designed and how they end up being worked now. 

 

There is also the complicating issue of the change at the bottom with the locks being converted from an 8 rise to a 6 rise, with the seventh chamber becoming  a triangular lock quite a bit deeper than the original. It is no longer possible to descend the 7th and 8th chambers and the 6th chamber has only a small fall - this will have a knock on effect back into the 5th and 4th chambers as the 5th chamber can't completely drain and thus the 4th chamber seems to overfill the 5th. Most boats are fairly shallow draft, so they probably don't need to be too precise on levels, and certainly the lock keepers seemed fairly relaxed about whether there was a foot of freeboard or whether water was cascading over the lock gates. 

 

I haven't seen them set up the flight at the start of the day, but at lunch time today (1pm to 2pm sharp) the flight had some water in each lock, and just after lunch a maintenance boat came down. But there may have been boat movements before them. I noticed the lock keepers didn't seem to correct the set up when boats followed each other or changed direction, other than when ascending they made sure that the chamber ahead of the boat was drained, presumably in part for safety reasons given the way the gate paddles work. There is a control pedestal at each pair of gates, but these can work the paddles on more than one lock, last night the entiire flight was drained by the keeper opening all the paddles from one pedestal! (and there was a heck of a lot of water at the bottom for a few minutes!). This means that the lock keepers  can do a lot of tinkering with the levels without it being that obvious.

40 minutes ago, Pluto said:

what's the French for a tape measure, then you can buy one and get more exact details. 

? I would put the clappy hand smiley but I can't find it!

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Ifyou can get there, the Libron crossing will certainly intrigue you. It is less than a mile from the town/village of Vias, on the way to Arles. The structure, including a floating river channel, allowed the canal to remain undamaged even when the River Libron was in flood and likely to overflow into the canal. The river is divided into two channels which normally pass through the canal. During floods, the boat is moved into place over one of the channels and the flood waters allowed to pass over the canal through the channel on the boat. Andreossy's drawing published in 1804 is below.

Libron crossing.jpg

Edited by Pluto
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15 hours ago, magpie patrick said:

Which is on my wish list once your translation hits the bookshops...

 

I've been so fascinated with the set up that I've only so far looked at the canal between L'ecluse Bezier (the western end of the Orb aqueduct diversion) and the top of the Staircase, about four miles of canal and river if you include both routes. It's intriguing watching boats go up and down and, on Saturday, boats were following each other up and down which probably means the regime is varied from that of a single boat passage. In any event, there is a difference between how the locks were intended to be worked when they were designed and how they end up being worked now. 

 

There is also the complicating issue of the change at the bottom with the locks being converted from an 8 rise to a 6 rise, with the seventh chamber becoming  a triangular lock quite a bit deeper than the original. It is no longer possible to descend the 7th and 8th chambers and the 6th chamber has only a small fall - this will have a knock on effect back into the 5th and 4th chambers as the 5th chamber can't completely drain and thus the 4th chamber seems to overfill the 5th. Most boats are fairly shallow draft, so they probably don't need to be too precise on levels, and certainly the lock keepers seemed fairly relaxed about whether there was a foot of freeboard or whether water was cascading over the lock gates. 

 

I haven't seen them set up the flight at the start of the day, but at lunch time today (1pm to 2pm sharp) the flight had some water in each lock, and just after lunch a maintenance boat came down. But there may have been boat movements before them. I noticed the lock keepers didn't seem to correct the set up when boats followed each other or changed direction, other than when ascending they made sure that the chamber ahead of the boat was drained, presumably in part for safety reasons given the way the gate paddles work. There is a control pedestal at each pair of gates, but these can work the paddles on more than one lock, last night the entiire flight was drained by the keeper opening all the paddles from one pedestal! (and there was a heck of a lot of water at the bottom for a few minutes!). This means that the lock keepers  can do a lot of tinkering with the levels without it being that obvious.

? I would put the clappy hand smiley but I can't find it!

A tape measure in French is “un mètre”.

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I arrived at the locks this morning (I'm staying about 5 minutes walk away) to see  maintenance boat just finish the descent and then two hire boats go up. Regarding the operaion I noticed they "set" the flight for the ascent by filling the top four chambers to the brim, The keeper then filled the bottom (sixth) chamber from the fourth, fifth from the third etc, rather like we operate staircases except with a chamber gap between the boats and the chanber being emptied. 

 

Edited to add - I think I've got the sums right  in my head - this is what I observed and it should work - draining say, the 2nd lock completely will fill the fourth from navigable depth and also put navigable depth in the third, but with the control panels the lock keeper can get extra water down without anyone notcing much.

 

The lock keeper was rather cavalier about the exact levels for the passage, lertting boats move between chambers when there was still a lot of water coming through. 

 

I was going to take the bus to Colombiers, but the weather has been beatiful today, and a kiosk by the locks was selling good coffee, and boats were going up and down....

 

I have "done" the Beziers section these few days, but not left the town, tomorrow I must travel to Perpignan to meet friends for the remainder of my trip. I have resolved to come back and do it properly, possibly even in a boat. Ryanair fly from Bristol, £10 and I can bring a camera and a change of socks- for rather more I can bring some luggage.

 

I've ordered LTC Rolt's from Sea to Sea, to make sure I'm better informed next time - I'll probably tap up Pluto for some extra info as well!

 

 

 

Edited by magpie patrick
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My wife and I hired a boat on the Midi from just below Montpellier to Negra in 2016, a one way trip. Your photograph brought back memories of that trip, especially passing through those locks. The keepers don't mess around, once the next chamber was half empty they opened the gates, high speed locking. I don't know whether it is the shape of the lock chamber but it didn't throw the boat around. A wonderful canal and if you think hire boaters provide entertainment on the UK canals you haven't seen anything until you visit the Midi.

 

Ken 

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