Trent & Mersey locks

[Arthur Marshall]

There must be a design difference between the T&M locks each side of the summit. South of Stoke there's no undertow when going up, north it's decidedly dangerous to start with more than half a paddle. The effect is presumably worse in a small boat like mine as there's more room to move, but why the discrepancy ? Is it where the ground paddle water enters the lock or something else? Anyone know?

[Captain Pegg]

12 minutes ago, Arthur Marshall said:

There must be a design difference between the T&M locks each side of the summit. South of Stoke there's no undertow when going up, north it's decidedly dangerous to start with more than half a paddle. The effect is presumably worse in a small boat like mine as there's more room to move, but why the discrepancy ? Is it where the ground paddle water enters the lock or something else? Anyone know?

I’ll test the theory about the locks south of Stoke this week. To be honest I’ve always thought that all T&M narrow locks have a tendency to draw the boat forward.

 

I think it’s because water enters the chamber underneath the baseplate. Oxford and S&W locks do similar.

 

It is subtle though because with a small boat you can stay behind the affected area. But get it wrong and you’ll be accelerated into the top gate/cill at speed. I’ve certainly had that problem ascending the locks between Fradley and Great Haywood.

 

Being at the helm is also no help since with water under the baseplate there’s pretty much nothing that can be done using the engine. That’s why I think you have more control over a boat in a lock being on the lockside with a line and able to quickly manipulate the paddles.

 

I’ve tried all sorts to counteract this problem with variable and usually limited success.

[MoominPapa]

Fradley locks have a strong forward push.

 

MP.

 

 

[Higgs]

I hope no one is in a hurry to use the locks after I'm done. I open the paddles very gradually, until the boat has settled. Going up, and too quickly, the boat will be slammed against the top gate, from water passing underneath the boat, hitting the lower gates and returning.

 

 

Edited June 5, 2023 by Higgs

[beerbeerbeerbeerbeer]

3 hours ago, Captain Pegg said:

I’ve tried all sorts to counteract this problem with variable and usually limited success.

I’m sure you’ve tried it too, if I time it right opening the second paddle can stop the boat from gaining speed and then it creeps slowly forward

if I get it wrong …🤬

 

[TheBiscuits]

3 hours ago, Captain Pegg said:

I’ve tried all sorts to counteract this problem with variable and usually limited success.

 

Slide the stem up the plate on the gate.  The water movement holds the boat in place, just make sure you are touching before opening paddles and most importantly there's nothing sticking out of the plate!

[Ken X]

We have always rested the bow of the boat against the top cill or gate before opening a paddle.  We also take the centre line forward and, if possible take a turn around a handy bollard.  After cracking one paddle to check all is stable we open them fully.  As we are both at the top gates we can observe how the bow is riding in case of a hangup and both drop paddles simultaneously.  As the boat rises the slack generated in the centre line allows it to drift back a bit to clear handrails etc without risk of touching at the stern.  It then tightens a tad to bring it forward prior to exit.  Again, we can adjust if required.

Works for us but always good to hear other methods.

[Stilllearning]

3 hours ago, Captain Pegg said:

I’ll test the theory about the locks south of Stoke this week. To be honest I’ve always thought that all T&M narrow locks have a tendency to draw the boat forward.

 

I think it’s because water enters the chamber underneath the baseplate. Oxford and S&W locks do similar.

 

It is subtle though because with a small boat you can stay behind the affected area. But get it wrong and you’ll be accelerated into the top gate/cill at speed. I’ve certainly had that problem ascending the locks between Fradley and Great Haywood.

 

Being at the helm is also no help since with water under the baseplate there’s pretty much nothing that can be done using the engine. That’s why I think you have more control over a boat in a lock being on the lockside with a line and able to quickly manipulate the paddles.

 

I’ve tried all sorts to counteract this problem with variable and usually limited success.

I boated these locks, and many others, first with a 32ft tug, then with 50, 55 and 57 ft boats and almost always found the boat pulled forward when ascending.

With advice from my cousin who began boating in the 60s I got into the habit of going to the front of the lock, left the engine in gear at tickover and set the lock while holding on to the centre rope at all times. This was learned after one too many times high speed ramming  the cill.

[Captain Pegg]

12 minutes ago, TheBiscuits said:

 

Slide the stem up the plate on the gate.  The water movement holds the boat in place, just make sure you are touching before opening paddles and most importantly there's nothing sticking out of the plate!

First time I ventured north of Fradley in Vulpes I had my then 10yo daughter on the counter and having positioning centrally in the first lock got a massive forward pull that gave the boat and her a right bash.

 

So I then tried what you suggest at subsequent locks but at Colwich or Great Haywood got the bow fender caught in the cill and  had to very quickly shut down the paddles and let water out to free it. That’s an issue with having such low freeboard as the bits that can snag at the front of the boat can catch things that most boats will oversail.

 

Hence I don’t favour that approach. I’m not a big fan of boats riding either up and or down gates unless there’s really no option. It requires a lot of vigilance.

Edited June 5, 2023 by Captain Pegg

[Rob-M]

Boating regularly between Fradley and Stone I sit at the back of the lock if there are two of us and do half paddle, wait for boat to settle and then continue with the paddles.  If I am on my own I take the centre line and put a turn around the gate beam with the bow fender on the gate. I never leave the boat in gear and I really don't like to have to rev the engine when in a lock.

[David Mack]

3 hours ago, Captain Pegg said:

But get it wrong and you’ll be accelerated into the top gate/cill at speed.

One of the advantages of a full lengthboat is that even if the paddle flow does accelerate the boat forwards (or backwards), there isn't enough distance for the boat to have gained any significant speed before it reaches the gate.

On a previous 48ft boat I found that, going up or down, if you took the boat up to touching the gate/cill at the far end, and left it out of gear it would stay on the gate as the lock filled or emptied, only starting to drift back when the lock was half full/empty, by which time the strength of the flow had reduced. It rarely moved back far enough to catch the stern, and going down the rudder was below the cill by this point anyway. Didn't mean I didn't keep an eye on the boat anyway, but I rarely had to intervene.

[Captain Pegg]

35 minutes ago, Goliath said:

I’m sure you’ve tried it too, if I time it right opening the second paddle can stop the boat from gaining speed and then it creeps slowly forward

if I get it wrong …🤬

 

Yes. I’ve also found that one paddle or two you still can’t win.

 

Open one and the boat seems to float back further before it gets drawn forward. Open both it’ll accelerate quicker but start from a more forward position. With Vulpes I use a line but with longer boats caution with the paddles is the order of the day. Particularly until I’ve got used to what the boat in question is going to do. 
 

I‘ve also tried opening one paddle and then shutting it down as the boat starts its forward motion.

 

I think it’s more than the wave being reflected off the bottom gate. That is a very noticeable phenomenon on Worcester & Birmingham locks but on those you’re much more likely to hit the bottom gates and you can control the boat on the engine if you so desire. That doesn’t work on the T&M. The wave may start the motion but I think the severity of the movement is a result of the boat also being lifted by inflowing water underneath.

 

8 minutes ago, David Mack said:

One of the advantages of a full lengthboat is that even if the paddle flow does accelerate the boat forwards (or backwards), there isn't enough distance for the boat to have gained any significant speed before it reaches the gate.

On a previous 48ft boat I found that, going up or down, if you took the boat up to touching the gate/cill at the far end, and left it out of gear it would stay on the gate as the lock filled or emptied, only starting to drift back when the lock was half full/empty, by which time the strength of the flow had reduced. It rarely moved back far enough to catch the stern, and going down the rudder was below the cill by this point anyway. Didn't mean I didn't keep an eye on the boat anyway, but I rarely had to intervene.

Absolutely, it is worse with a short boat. I tend to find attempting to ride up the gate in neutral results in a constant bouncing onto and off the gate. That’s OK providing you’re careful with the paddles to limit the force.

 

Another reason for not putting a short boat in gear against the top gate is that if it snags you might have no means - other than uncontrolled descent onto the roof - of getting back to the controls in case of emergency.

 

 

Edited June 5, 2023 by Captain Pegg

[Alan de Enfield]

28 minutes ago, TheBiscuits said:

 

Slide the stem up the plate on the gate.  The water movement holds the boat in place, just make sure you are touching before opening paddles and most importantly there's nothing sticking out of the plate!

 

The 1st time we ever hired was from Middlewich Boats (many moons ago) and their instruction was "when going up in locks, go to the front of the lock and let the fender button touch the gate, or sill, engage forward gear at tickover and let the boat slide up & as the water rises, there could be a slight bump as the bow rides over the cill and touches the gate.).

[Captain Pegg]

4 minutes ago, Alan de Enfield said:

 

The 1st time we ever hired was from Middlewich Boats (many moons ago) and their instruction was "when going up in locks, go to the front of the lock and let the fender button touch the gate, or sill, engage forward gear at tickover and let the boat slide up & as the water rises, there could be a slight bump as the bow rides over the cill and touches the gate.).

With someone at the helm that’s probably fine but I would never do that single handed.

 

As I’m sure you know when things go wrong it happens very quickly. Paddles, centre line and controls is too much stuff and too far apart for one person to deal with.

ETA - I’m sure people do it when single handing but my experience of a couple of snaggings makes me wary.

Edited June 5, 2023 by Captain Pegg

[beerbeerbeerbeerbeer]

I will let the boat ride up the gate 

But the problem is the boat being short at 48’ will speed up and bang the cill if I don’t get it just right. 
sometimes I can step off back and get to the top paddles before it hits and raise the paddle to stop/slow the boat. 
Or take a rope with me and give it a turn around something. 
 

I find there’s no one answer. 
Depends on the locks, the weather and whether I’m generally having a good day and feeling energetic. 
 

Fortunately I’m always on the same boat so I don’t have to rethink and relearn according to the behaviour of yet another boat.  

 

[Arthur Marshall]

20 minutes ago, Captain Pegg said:

With someone at the helm that’s probably fine but I would never do that single handed.

 

As I’m sure you know when things go wrong it happens very quickly. Paddles, centre line and controls is too much stuff and too far apart for one person to deal with.

ETA - I’m sure people do it when single handing but my experience of a couple of snaggings makes me wary.

I'm usually single-handed, but not this trip. Every lock south of Stoke, with ground paddle full up followed immediately by gate or ground paddle full up, left me sitting comfortably at the back of the lock with no surge forward whatsoever. No engine use, no ropes.

As my boat's been nearly sunk several times by well meaning friends showing me how to ride the gate, I wouldn't do that for a million quid. I'm sure it works perfectly 99 times out of a hundred, though.

[Captain Pegg]

5 minutes ago, Arthur Marshall said:

I'm usually single-handed, but not this trip. Every lock south of Stoke, with ground paddle full up followed immediately by gate or ground paddle full up, left me sitting comfortably at the back of the lock with no surge forward whatsoever. No engine use, no ropes.

As my boat's been nearly sunk several times by well meaning friends showing me how to ride the gate, I wouldn't do that for a million quid. I'm sure it works perfectly 99 times out of a hundred, though.

I’m glad it’s not just me. I’ll be on that stretch tomorrow. I’m much much more familiar with the locks south of Great Haywood that do suffer that characteristic. I’ll see what happens in various positions as I know you can avoid the pull by staying back on S&W locks. Length of the boat is a factor.

 

[nicknorman]

Telemachus has a good reverse so we sit very near the back of the lock and just open one paddle then the other. The important thing is to engage reverse as soon as you feel the bow dip and before it starts to move forward, then not much revs needed to hold station. If you are dozy and let it get a few feet forward, then it can be difficult to get it back again.

 

I think it’s important to realise that the boat moves forwards because the flowing water suffers a decrease in pressure (Bernoulli’s effect) so the level at the front of the lock drops, putting a slope onto the water, and the boat slides down the slope. So the first thing that happens is the bow dips, second thing is the boat starts to accelerate, third thing is it’s moving forward significantly. If you catch it at the first thing, all is sweetness and light but if not…

 

If I’m doing it single handed, which is rare, I use a line/bollard to hold the boat back.

 

I am not keen on the riding the gate thing for the reasons already mentioned.

[MrsM]

We also tend to sit towards the front of the lock when ascending to reduce the risk of being drawn forward. However 2 years ago the button fender briefly caught on a protruding timber at a lock near Chester. This has taught us to be super alert and I don't think I would be happy doing this single--handing. It's obviously easier when one of you is on the paddles and the other ready to engage astern if this happens again. No safer approach than very slowly opening paddles and seeing how boat behaves IMO. 

[cuthound]

I once shared a lock with Ike Argent (who was single handing) on Amy the Pup on the northern end of the Shroppie.

 

He prevented his boat from being pulled forward by using a line with a hook on the end between a stern dolly and the gate paddle gear and leaving the boat in gear. As the lock filled the line allowed his boat to move forward but not enough to contact the front gates.

Edited June 5, 2023 by cuthound
Missing letter

[Rob-M]

I have chucked a loop over a lock bollard at the rear end of a lock but it isn't something I regularly do.  It does allow all the paddles to be whacked up though without worry the boat is going to smash a gate.

[Captain Pegg]

3 hours ago, nicknorman said:

Telemachus has a good reverse so we sit very near the back of the lock and just open one paddle then the other. The important thing is to engage reverse as soon as you feel the bow dip and before it starts to move forward, then not much revs needed to hold station. If you are dozy and let it get a few feet forward, then it can be difficult to get it back again.

 

I think it’s important to realise that the boat moves forwards because the flowing water suffers a decrease in pressure (Bernoulli’s effect) so the level at the front of the lock drops, putting a slope onto the water, and the boat slides down the slope. So the first thing that happens is the bow dips, second thing is the boat starts to accelerate, third thing is it’s moving forward significantly. If you catch it at the first thing, all is sweetness and light but if not…

 

If I’m doing it single handed, which is rare, I use a line/bollard to hold the boat back.

 

I am not keen on the riding the gate thing for the reasons already mentioned.

What do you think is different in particular about T&M, Oxford and S&W locks where this forward pull occurs and say BCN and W&B locks where it doesn’t?

[nicknorman]

8 minutes ago, Captain Pegg said:

What do you think is different in particular about T&M, Oxford and S&W locks where this forward pull occurs and say BCN and W&B locks where it doesn’t?

Well some of the BCN locks have multiple ground paddle outlets including behind the bottom gates. But otherwise (and I’m totally guessing!) it might be to do with the direction the water comes out of the paddle culvert. If the water comes out pointing across the lock, the flow will be turbulent, just thrash around as it bounces off the opposite wall etc, and so Bernoulli doesn’t really kick in. But if the flow is directed more along the bottom of the lock, then the flow will be more laminar and that is when you get the Bernoulli effect.

[IanD]

2 hours ago, nicknorman said:

Well some of the BCN locks have multiple ground paddle outlets including behind the bottom gates. But otherwise (and I’m totally guessing!) it might be to do with the direction the water comes out of the paddle culvert. If the water comes out pointing across the lock, the flow will be turbulent, just thrash around as it bounces off the opposite wall etc, and so Bernoulli doesn’t really kick in. But if the flow is directed more along the bottom of the lock, then the flow will be more laminar and that is when you get the Bernoulli effect.

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... 😞

[David Mack]

2 hours ago, nicknorman said:

Well some of the BCN locks have multiple ground paddle outlets including behind the bottom gates.

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.

Edited June 5, 2023 by David Mack