Trent & Mersey locks

[nicknorman]

6 minutes ago, David Mack said:

I believe Perry Bar were built with multiple top paddle outlets along the length of the lock including one behind the bottom gates. This was done to save the boatman time since raising the top paddles would shut the bottom gates automatically. But these outlets have been blocked off due to the risks of balance beams moving and striking a person when there is nobody working the lock nearby.

Also on the Garrison locks, and some of these still work.

14 minutes ago, IanD said:

I don't think it's Bernoulli because the water speed is far too low, it's that if the paddles direct water down the lock under the boat it piles up at the bottom of the lock and lifts the stern, which pushes the boat forwards in the lock as it slides down the slope.

 

If you watch the level of the boat compared to the (level) joints in the stonework you can see this happen as the boat tilts up at the stern -- by which time it's often too late as the boat accelerates towards the cill... 😞

I disagree. If it were as you say, the effect would be at a maximum near the back of the lock, whereas in fact it is at a maximum near the front of the lock. With a dense fluid (the water) and much less dense fluid above (the air) the effect doesn’t require a high water velocity to create the sloped interface (and let’s bear in mind the slop is only a few degrees).

There is a general increase in level caused by the water flowing in, but then the bow dips

[ditchcrawler]

12 minutes ago, nicknorman said:

Also on the Garrison locks, and some of these still work.

 

I would say most of them. Also one up the Caldon has multiple outlets as do the GU wide locks at Stockton  

[Captain Pegg]

9 minutes ago, ditchcrawler said:

I would say most of them. Also one up the Caldon has multiple outlets as do the GU wide locks at Stockton  

GU Birmingham line locks have four (I think) outlets along the length of the opposite wall to the paddle. Hence you only work the side the boat is on when ascending with one boat.

 

Wonderfully controllable locks. Four turns to gently close any gates that have drifted partially open and another four to bring the boat gently against the side. Then the rest.

 

Beware Bascote staircase and Knowle. Different paddle sizes and gearing on those but they work the same way.

[stagedamager]

The Cheshire locks have the paddle holes further back I believe. The knobstick boats were build with massive deck beams and strong fore end knees to take the shock of the surge of water slamming the boats into the cill.

 

Kind regards

 

Dan

[IanD]

7 hours ago, nicknorman said:

Also on the Garrison locks, and some of these still work.

I disagree. If it were as you say, the effect would be at a maximum near the back of the lock, whereas in fact it is at a maximum near the front of the lock. With a dense fluid (the water) and much less dense fluid above (the air) the effect doesn’t require a high water velocity to create the sloped interface (and let’s bear in mind the slop is only a few degrees).

There is a general increase in level caused by the water flowing in, but then the bow dips

That's not the Bernoulli effect, which is a drop in pressure within a confined body of liquid as the velocity increases -- for example, when liquid travels through a constriction.

 

Wherever it happens in the lock -- front or back -- the cause is indeed a slope in the water surface which the boat slides down, but this is simply caused by the water flowing into the lock and then slowing down. You'd see the Bernoulli effect inside the ground paddle sluices if you measured the pressure inside them. 

[davidg]

9 hours ago, Captain Pegg said:

GU Birmingham line locks have four (I think) outlets along the length of the opposite wall to the paddle. Hence you only work the side the boat is on when ascending with one boat.

 

Wonderfully controllable locks. Four turns to gently close any gates that have drifted partially open and another four to bring the boat gently against the side. Then the rest.

 

Beware Bascote staircase and Knowle. Different paddle sizes and gearing on those but they work the same way.

 

The outlets are on the same side as the paddle. The water flows out, under the boat if there is one in the lock, hits the opposite wall and boils up there; you can see this happening in sequence down the lock when you lift a paddle. They are wonderful, controllable and quick - Hatton in 90 minutes, what would Canalplan say?

[nicknorman]

2 hours ago, IanD said:

That's not the Bernoulli effect, which is a drop in pressure within a confined body of liquid as the velocity increases -- for example, when liquid travels through a constriction.

 

Wherever it happens in the lock -- front or back -- the cause is indeed a slope in the water surface which the boat slides down, but this is simply caused by the water flowing into the lock and then slowing down. You'd see the Bernoulli effect inside the ground paddle sluices if you measured the pressure inside them. 

You’ve more or less just said it’s Bernoulli!

 

I think your experience of Bernoulli is limited to eg a carburettor or Venturi pump, where the fluid is contained in a pipe etc. When the fluid is not contained and there is a boundary with another fluid of different density (the air above) then things are slightly different. The air pressure remains constant as it has no flow (massive velocity gradient at the interface between the different fluids) but the water pressure decreases with its velocity (conservation of energy aka Bernoulli) and so the air pressure above pushing down causes the boundary to lower near the front. Nearer the back of the lock the fluid has slowed as its dispersed into the increasing volume of water, the effect becomes less.

 

same sort of concept as how a ping pong ball on a string is counter-intuitively sucked into a flow of water from a tap, as opposed to being pushed away by the water.

 

Edited June 6, 2023 by nicknorman

[Arthur Marshall]

Interesting and educational, this thread. I'd always assumed that the water comes in and makes a wave, the boat sits on that and goes to the back of the lock on it and then rides it forward when it bounces off the back gate. Never thought of a slope.

Glad I finally, after all these years, got round to asking .

[Captain Pegg]

3 hours ago, davidg said:

 

The outlets are on the same side as the paddle. The water flows out, under the boat if there is one in the lock, hits the opposite wall and boils up there; you can see this happening in sequence down the lock when you lift a paddle. They are wonderful, controllable and quick - Hatton in 90 minutes, what would Canalplan say?

I wasn’t sure they were deep enough for that. But it is the case that even if you open the opposite paddle when the lock is mostly full it will still push the boat away from the wall and that’s much better explained by it flowing underneath and back.

[ditchcrawler]

If you go right to the front of the lock in gear and stand on the stern while someone draws the paddle, not one click and go for a cupper, a steady wind, you will see the bow rise a bit and the boat start to move back, but then it will drop by several inches and the stern will lift several inches and regardless of what you do the boat will stay against the top gate. The slope is very pronounces, a single hander working the lock their self would not see this.

[Pluto]

On L&LC locks a cleat was provided so that the boat could be held forward by a line from the ludget - the towing mast on a narrow boat, but mainly used for control in locks on the L&LC, which is why motor boats had them. You can also see the slapping post which stopped the balance beam in the same position when closing the gates and ensured a good fit to the mitre every time. I believe a pleasure boater was killed by trapping around 1960 as almost all of them were removed around that time. On the towpath side, an iron bar from the mitre post helped keep the towing lines clear of the paddle, while the staple on the offside was the final rung in a series which allowed boatmen to climb up the gates. They certainly made it easier to work locks when single-handed.

[Captain Pegg]

13 minutes ago, ditchcrawler said:

If you go right to the front of the lock in gear and stand on the stern while someone draws the paddle, not one click and go for a cupper, a steady wind, you will see the bow rise a bit and the boat start to move back, but then it will drop by several inches and the stern will lift several inches and regardless of what you do the boat will stay against the top gate. The slope is very pronounces, a single hander working the lock their self would not see this.

I think most single handers will be familiar with what happens when you put a boat into a bridge hole below a lock, draw it up to gates and then empty  the lock. That’s pretty much the same thing as you describe.

 

I also note that if I draw one paddle fully that the boat will list to one side and on mine that means water can overtop onto the tug deck.

[Richard Fairhurst]

13 hours ago, Captain Pegg said:

GU Birmingham line locks have four (I think) outlets along the length of the opposite wall to the paddle. Hence you only work the side the boat is on when ascending with one boat.

 

Wonderfully controllable locks. Four turns to gently close any gates that have drifted partially open and another four to bring the boat gently against the side. Then the rest.

 

Absolutely. We did Hatton through to Napton last week and you can basically work them like narrow locks. Easier, in fact, as you don't have to cross to the other side to open/close the mitred gate – you can just stay on the towpath side.

 

The Ham-Baker gear could be easier to wind (as everyone says it was once), and the locks with wooden balance beams rather than metal ones feel heavy and unbalanced. Hatton paddles will drop slowly down without a windlass as designed, but some of the others now just spin out of control unless you wind them down. But maintenance aside, the design is brilliant.

 

Sorry to see that Ham-Baker finally went under last year, though it looks like parts of the company have been bought out: https://www.thebusinessdesk.com/westmidlands/news/2069594-fifty-jobs-preserved-through-sale-of-ham-baker-businesses

Edited June 6, 2023 by Richard Fairhurst

[David Mack]

18 minutes ago, Richard Fairhurst said:

Sorry to see that Ham-Baker finally went under last year, though it looks like parts of the company have been bought out: https://www.thebusinessdesk.com/westmidlands/news/2069594-fifty-jobs-preserved-through-sale-of-ham-baker-businesses

Not the first time the company has changed hands. They traded from a Westminster address, but the factory was canalside at Oldbury until they were bought out and moved to their current Stoke site.

https://madeinoldbury.co.uk/articles/ham-baker-co-ltd/

 

[Captain Pegg]

The locks coming up from Great Haywood are configured with one ground and one gate paddle at the top. This is the same as Wood End, Colwich and Great Haywood. Shade House and Middle locks (and maybe others) at Fradley that do have a forward pull to the top gate have two ground paddles and no gate paddles.

 

In Hoo Mill, Weston and Aston locks I was far enough back such that I could open the ground paddle followed immediately by the gate paddle with no problems.

 

At Sandon I was further forward on account of the position of the lock ladder and after drawing the ground paddle was pulled onto the cill - albeit not severely - and had to wait for the boat to rise before drawing the gate paddle.

 

I think the Cheshire locks have two ground paddles (although there are likely differences within them).

Edited June 6, 2023 by Captain Pegg

[beerbeerbeerbeerbeer]

Those are some of my favourite locks and when there’s no one about I do them as slow as I can, savouring the moment. 
Lovely to do. 
 

Colwich can get very busy mind. 

 

I think they all have a bridge at the bottom?

 

Aston don’t have bridge though. 

Edited June 6, 2023 by Goliath

[Rob-M]

6 minutes ago, Goliath said:

Aston don’t have bridge though

Aston Lock does have a bridge, it is a split bridge but I don't think the split is clear enough to pass a rope through.

[beerbeerbeerbeerbeer]

Ah ok,
Yes, a small foot (?) bridge, split bridge. 

But no proper bridge hole?

The others have bridge holes which is what makes it so nice for single handing. 

 

 

[Tracy D'arth]

The pulling forward of a boat in the Cheshire locks I believe is due to the ground paddle culvert discharge being closer to the top gates. The turbulent water will support less weight than still water and the bow effectively drops into a hole causing the boat to run down hill into the gates.

This is very noticeable in Wardle lock on the Middlewich branch which was a grading lock for toll measurements and is longer than the rest.

[Rob-M]

Just now, Goliath said:

Ah ok,
Yes, a small foot (?) bridge, split bridge. 

But no proper bridge hole?

The others have bridge holes which is what makes it so nice for single handing. 

 

 

Yes, very easy to step on or off under the proper bridges.

[beerbeerbeerbeerbeer]

32 minutes ago, Rob-M said:

Yes, very easy to step on or off under the proper bridges.

It’s got me thinking now:

I’m gonna dare say all locks from Alrewas upto Stoke have a bridge hole with only a few having a split bridge. 
 

I’m trying in my head to picture the ones above Stone 

 

and of course there are those with both. 
is great Haywood the only one where you step over the bottom gates? (or walk around?)

Edited June 6, 2023 by Goliath

[Stroudwater1]

22 minutes ago, Goliath said:

It’s got me thinking now:

I’m gonna dare say all locks from Alrewas upto Stoke have a bridge hole with only a few having a split bridge. 
 

I’m trying in my head to picture the ones above Stone 

One of the lower Cheshire locks by Sandbach/ M6 last year 

 

 

Back the question, all locks we do I manage to stay roughly in the middle of the lock. I don’t like to be too near the gates. We have poor reverse and the only way we could sensibly go up Cheshire locks was to press on the cill and use fastish forward. I don’t like doing this. Using a line was pretty hopeless. 

Incidentally the second lock going up Hillmorton seems to have the same effect, the top and bottom locks don’t for some reason and I can easily stay in the middle. I think the middle are a bit deeper but it seems the right is worse ascending compared to the left?  

[Mike Todd]

1 hour ago, Rob-M said:

Aston Lock does have a bridge, it is a split bridge but I don't think the split is clear enough to pass a rope through.

May have a split in the bridge deck but not in the now obligatory handrails either side.

[Heartland]

The Trent & Mersey Canal route is one that was constructed and reconstructed over time. That from Great Hayward towards Alrewas was the first to be made with construction proceeding beyond Burton as barge width locks and a river section at Alrewas- Wichnor.

The work north of Harecastle was chiefly made later (Preston Brook being an exception). The duplication of the locks and the replacement of the staircase locks was also later.

The foot bridge image was part of the later improvements with the engineer Trubshaw involved

Such variations are detailed in my book. 

[davidg]

1 hour ago, Stroudwater1 said:

Incidentally the second lock going up Hillmorton seems to have the same effect, the top and bottom locks don’t for some reason and I can easily stay in the middle. I think the middle are a bit deeper but it seems the right is worse ascending compared to the left?  

 

It depends which side you go. One side of each pair fills/empties much quicker than the other. It isn't the same side at each pair and no I'm not going to say which side on a public forum because:

 

a) It can be dead handy for overtaking people if you know🙂

 

b) You have to pay your dues by being overtaken and scratching your head at the top/bottom working out what just happened rather than finding out the lazy way on t'internet🙂🙂