Lock gate chains - function?

[magpie patrick]

Attached is a crop of a photo showing the top gates of a broad lock with chains from the mitre to the bank - on the nearer side you can see the chain is anchored at the back of the coping. Does anyone have any idea on their function?

 

They are too slack to bear any load whilst the lock is empty, and the lock has balance beams so using them to pull the gates open seems unlikely. I guess the chains would sink as the gates opened so they are not in the way. 

 

Thoughts please?

 

Edited March 11, 2021 by magpie patrick

[Jen-in-Wellies]

Was this a dodgy area? Is it to stop someone stealing the lock gates? ?

[Ray T]

Would they have been attached to a capstan at one time?

[David Mack]

To stop boats hitting the gates?

[Pluto]

The angle of the mitre seems very flat, so could it have been a safety device to protect against the gates failing? The full photo would help, as it may confirm Ray's suggestion. The chains do look at little large compare to others I have seen for opening gates, but still possible.

[matty40s]

40 minutes ago, David Mack said:

To stop boats hitting the gates?

Slowing down a loaded pair before they hit the gates.

[MoominPapa]

At least some of the locks on the Weaver still have them. Marsh lock for certain. 

 

I've always assumed that they're a safety device to support the otherwise unsupported corner of the gate should it become loaded without the opposite gate closed so that both are supported by arch action. When that would be needed  is less obvious, apart from maybe collision with the gate?

 

MP.

 

ETA some gates on eg the L&L have A frames downstream of the gates to provide support to the same corner of the gate.

Edited March 11, 2021 by MoominPapa

[BWM]

This may have been to hold the vates open in times of severe flooding, have seen similar on rivers in flood.

[TheBiscuits]

 

Weight to assist opening the gates?  The chains look very heavy duty for anything else.

 

One of the locks on Wigan Flight has chains and sliding counterweights to do this, but outside the lock chamber so the chain is attached to the beam not the mitrepost.  

 

This does assume it's a one-off for that particular lock and not common to all the locks in the area. 

 

 

[magpie patrick]

It's Bradford Lock, K&A, I'm going to have another look on Saturday, I'm fairly sure  I've seen the anchor point by the lock, a staple embedded in the lock side. I'm also sure I've never seen any remains of a capstan and also sure the K&A never had them.  I didn't specify the canal as I wanted generic answers!

The sag on the chains suggests to me they aren't to lend strength to the mitre, the gates would have bent a heck of a long way back before the chain became taught and restricted further movement.

 

9 minutes ago, TheBiscuits said:

 

Weight to assist opening the gates?  The chains look very heavy duty for anything else.

 

 

Interesting idea that I hadn't thought of - I guess the chains would pull the gates open slightly by default even if that was not their intended purpose

 

9 minutes ago, TheBiscuits said:

 

This does assume it's a one-off for that particular lock and not common to all the locks in the area. 

 No idea, but then I didn't know about these until this morning! I'm going to walk past several K&A locks in the next few weeks to see if there is evidence anywhere else for these chains

 

2 hours ago, Pluto said:

The angle of the mitre seems very flat, so could it have been a safety device to protect against the gates failing? The full photo would help, as it may confirm Ray's suggestion. The chains do look at little large compare to others I have seen for opening gates, but still possible.

 

Pluto - I thought you'd know! You know EVERYTHING!   or at least everything that I don't  It's not often that neither of us has the answer! 

2 hours ago, David Mack said:

To stop boats hitting the gates?

 I'd wondered that too

Edited March 11, 2021 by magpie patrick

[Derek R.]

I think Pluto has it.

We had an incident at Gargrave once where entering a full lock going down the bottom gate mitre face over-run its mate. The gate twisted alarmingly and let a lot of water out very quickly. We sank a foot or so before being able to warn a second boat that was intending to join us and close the top gates.

 

A set of such chains would have prevented the incident from happening. We phoned Waterways who seemed very nonchalant about the whole affair.

[TheBiscuits]

12 minutes ago, Derek R. said:

I think Pluto has it.

We had an incident at Gargrave once where entering a full lock going down the bottom gate mitre face over-run its mate. The gate twisted alarmingly and let a lot of water out very quickly. We sank a foot or so before being able to warn a second boat that was intending to join us and close the top gates.

 

A set of such chains would have prevented the incident from happening. We phoned Waterways who seemed very nonchalant about the whole affair.

 

As @magpie patrick says above, there looks to be too much slack in the chains for that.  The gates could go a couple of feet past closed position before the chains were holding them.

 

I wonder if there was a reason to always leave the tail gates open when the lock was empty - the weight of the drooping chains would hold the gates fully open.

[magpie patrick]

I can see the chains might provide some passive support to the mitre, as their weight would pull the mitre outwards. A barge, or a breasted pair, would hit the chains first rather than the gates which might also help minimise impact.  If the gates do give however, the chains won't stop that

 

From the respones, it seems we can work out what effect they might have, but there is no knowledge of the intentions behind fitting them? 

 

In @Pluto's example, they would have a similar, but less pronounced effect to the slapper posts on northern locks. 

[David Mack]

2 hours ago, MoominPapa said:

 

ETA some gates on eg the L&L have A frames downstream of the gates to provide support to the same corner of the gate.

 

And on the Rochdale. And there are a number of locks where the fixings are still present although the A-frames are not.

[J R ALSOP]

There used to be some on the top gates of Knowle Locks in the early 60's.

[David Mack]

13 minutes ago, J R ALSOP said:

There used to be some on the top gates of Knowle Locks in the early 60's.

They'd gone by about 1974 when we moored on the offside above the locks.

[Scholar Gypsy]

Chains are used to open and close the locks on the MSC. I noticed this on a recent video.

[TheBiscuits]

14 minutes ago, Scholar Gypsy said:

Chains are used to open and close the locks on the MSC. I noticed this on a recent video.

 

Yeah, they are great.  The chap pulls a big lever, there's a sound of rushing water and then chains start to move to operate paddles and eventually gates.  I assume they are hydraulically driven by the canal water moving, which seems a simple but good idea.

[magnetman]

There are locks on the River Wey which have a framework below the tail gates to encourage the mitre to align correctly. One of these is the lock where the road crosses immediately below so it might be visible on street view. 

 

New Haw lock. The footbridge below the tail of the lock has an arrangement to support the gate mitre. Not a very good picture from Google but vaguely visible. 

 

 

 

 

I suspect that's the function of the chains and they were originally rather tighter than shown and perhaps adjustable. 

 

Obviously the top gates would have to be supported in a different way to the bottom gates. 

 

 

It's not so much to prevent total failure but to get the mitre to align correctly on gates which are less substantially built than some others. 

 

 

Edited March 13, 2021 by magnetman

[pearley]

18 hours ago, TheBiscuits said:

 

Yeah, they are great.  The chap pulls a big lever, there's a sound of rushing water and then chains start to move to operate paddles and eventually gates.  I assume they are hydraulically driven by the canal water moving, which seems a simple but good idea.

Isnt that how the Weaver Locks originally worked?

[Steilsteven]

I wonder if they were fitted to hold the gates open? The position of the strapping post in the bottom right of the photo makes me think that the chains would have been dropped behind these to prevent the gates from closing as a barge approached. Towney lock on the Kennet is very bad for doing this and would benefit greatly from such an arrangement.

 

Keith

[magpie patrick]

1 hour ago, Steilsteven said:

I wonder if they were fitted to hold the gates open? The position of the strapping post in the bottom right of the photo makes me think that the chains would have been dropped behind these to prevent the gates from closing as a barge approached. Towney lock on the Kennet is very bad for doing this and would benefit greatly from such an arrangement.

 

Keith

 

That's an interesting idea - I'd need to measure whether the chain was long enough with the gate open. Would anyone like to estimate how much length the "sag" adds to the length from the mitre to the anchor point as I could measure that on site (the anchor point is still apparent)