Oxford Canal - Broadmoor Lock

[alias]

11 Sept

 

Notice Alert

Oxford Canal
Location: Broadmoor Lock 24
Starts At: Lock 24, Broadmoor Lock
Ends At: Lock 24, Broadmoor Lock
Up Stream Winding Hole: Bridge 147
Down Stream Winding Hole: Bridge 153 Cropredy Wharf

Monday 11 September 2023 13:00 until further notice

Type: Navigation Closure
Reason: Boat damage

---

 

Original message:

 

Navigation closed due to damage to lock gate

Updates to follow

You can view this notice and its map online here:
https://canalrivertrust.org.uk/notice/26222/broadmoor-lock-24

You can find all notices at the url below:
https://canalrivertrust.org.uk/notices

 

This is the problem:

[magnetman]

Wasn't there an identical failure recently at Napton? 

 

 

This 

 

Exactly the same. 

Boat damage or maintenance failure

[Captain Pegg]

42 minutes ago, magnetman said:

Wasn't there an identical failure recently at Napton? 

 

 

This 

 

Exactly the same. 

Boat damage or maintenance failure

I doubt there is any specific maintenance regime for those components other than a basic inspection to see that everything remains fixed together and a functional test on the gate.

 

It looks like the bolt on the far side has failed which is consistent with a large load being applied to the gate when closed. A bit of corrosion and fatigue might not help but for it to fail by those factors in isolation under normal operation I’d suspect is unlikely.

[MtB]

3 minutes ago, Captain Pegg said:

It looks like the bolt on the far side has failed which is consistent with a large load being applied to the gate when closed.

 

Yes its beginning to look as though we might have a boater in in the area in the habit of taking a short run and ramming the gate open with the boat.

[magnetman]

19 minutes ago, Captain Pegg said:

I doubt there is any specific maintenance regime for those components other than a basic inspection to see that everything remains fixed together and a functional test on the gate.

 

It looks like the bolt on the far side has failed which is consistent with a large load being applied to the gate when closed. A bit of corrosion and fatigue might not help but for it to fail by those factors in isolation under normal operation I’d suspect is unlikely.

 

Yes the gate has been rammed. 

 

However, it seems to me the collar was designed with a sliding shock absorber setup which is in the black box. This presumably was to take account of incidents of gate ramming. The whole assembly is designed to move laterally. 

 

Do these collars still move? If not and they are seized then they are not being maintained and will not perform as intended. 

 

 

15 minutes ago, MtB said:

 

Yes its beginning to look as though we might have a boater in in the area in the habit of taking a short run and ramming the gate open with the boat.

 

To me it looks like the shock absorbers have seized up. 

I've not been on the Oxford for about 15 yars so have no idea if these collars still slide as designed. 

 

If they don't then they will fail. 

 

 

[MtB]

5 minutes ago, magnetman said:

However, it seems to me the collar was designed with a sliding shock absorber setup which is in the black box. This presumably was to take account of incidents of gate ramming. The whole assembly is designed to move laterally. 

 

 

Hmmm a perceptive observation. I've never attached any importance to those boxes, imagining they were just the top of the ground anchoring.

 

I've never seen under one of those covers.

[Captain Pegg]

6 minutes ago, magnetman said:

 

Yes the gate has been rammed. 

 

However, it seems to me the collar was designed with a sliding shock absorber setup which is in the black box. This presumably was to take account of incidents of gate ramming. The whole assembly is designed to move laterally. 

 

Do these collars still move? If not and they are seized then they are not being maintained and will not perform as intended. 

 

 

 

To me it looks like the shock absorbers have seized up. 

The anchoring of the collar involves some sort of spring arrangement because it’s designed to move as part of the balance system of the gate.

 

It’s logical to me that the gate has failed as you’d want it to fail. The repair on that looks pretty straightforward with three people, a tirfor, some hand tools, a set of replacement bolts and possibly a new collar.

 

If that arrangement were built to withstand a full on ramming of a heavy boat then the gate itself might fail and that’s an altogether more awkward proposition.

 

You have to have some kind of design threshold, not least so the installation is sensibly affordable.

 

 

[magnetman]

It is interesting how long the guide bar to the side is. It seems like originally these collars might have been designed to travel several inches under spring tension to protect the collar and gate. 

The further away half of the collar has sheared so unless they can weld it back together it definitely needs a new half which should be a stock item. 

 

Might be a welding job although it seems impossible to get enough strength doing that and it will just break again. 

[Captain Pegg]

13 minutes ago, magnetman said:

It is interesting how long the guide bar to the side is. It seems like originally these collars might have been designed to travel several inches under spring tension to protect the collar and gate. 

The further away half of the collar has sheared so unless they can weld it back together it definitely needs a new half which should be a stock item. 

 

Might be a welding job although it seems impossible to get enough strength doing that and it will just break again. 

it does look like quite an elaborate arrangement.

 

I wasn’t sure if the collar itself has fractured as the face where it has parted looks quite uniform - albeit it appears stepped.

 

I’d be amazed if CRT welded that sort of thing in situ.

[magnetman]

CRT do a lot of bodges these days...

 

The collar has sheared. There is a galvanised coachbolt securing the other end of it. 

 

Broadmoor lock collar: 

 

 

 

[Hudds Lad]

We came back up this lock a couple of weeks ago, and J asked me what was wrong with it, being a bit thick i had to have it explained to me (and the boat blocked my view forward, honest). The head gates were entirely leak free, not a single dribble to be seen. We found this odd as the pound above turned out to be about a foot and a half down. Sad that the best gates we've seen on the system so far have been knacked  

[magnetman]

I reckon original design was where that coach bolt is was a shear pin so a failure would break that and open up the collar also breaking the bolt on other side. Fix = new bolt and new pin. No worries. 

 

But the part by the coachbolt is probably stuck fast by corrosion so the collar itself shears. 

 

 

[alias]

1 hour ago, magnetman said:

I reckon original design was where that coach bolt is was a shear pin so a failure would break that and open up the collar also breaking the bolt on other side. Fix = new bolt and new pin. No worries. 

 

But the part by the coachbolt is probably stuck fast by corrosion so the collar itself shears. 

 

 

Reopened at 12.45.

 

It's raining and 40 boats waiting to go through, (with only one working bottom paddle at Broadmoor), so will probably wait until tomorrow.

[magpie patrick]

2 hours ago, magnetman said:

However, it seems to me the collar was designed with a sliding shock absorber setup which is in the black box. This presumably was to take account of incidents of gate ramming. The whole assembly is designed to move laterally. 

 

Do these collars still move? If not and they are seized then they are not being maintained and will not perform as intended. 

 

 

 

The problem is that this system was designed for a full length boat that might be able to move by two feet to ram the gate, possibly pushed by the water filling the lock. A shorter boat, with a longer run up, under engine power can probably deliver a lot more oomph

[PaulJ]

3 minutes ago, magpie patrick said:

 

The problem is that this system was designed for a full length boat that might be able to move by two feet to ram the gate, possibly pushed by the water filling the lock. A shorter boat, with a longer run up, under engine power can probably deliver a lot more oomph

I wondered if it was just a shorter and unrestrained  boat kept back from the gates with some over ethusastic paddle lifting that may have been the final straw for the collar breaking.

[MtB]

33 minutes ago, PaulJ said:

I wondered if it was just a shorter and unrestrained  boat kept back from the gates with some over ethusastic paddle lifting that may have been the final straw for the collar breaking.

 

The forward surge caused by over-enthusiastic paddle-lifting would result in a boat hitting the gate with the lock near-empty, and with a good head of water still on the other side to oppose the thump. I'm more inclined to think it is deliberate ramming of the gate by a short boat in a full lock. The only reason I can think of to do this would be to try to open it, possibly before a level has been quite reached. 

 

Well two reasons really. The other being a deliberate intention to cause damage.

[Tracy D'arth]

5 minutes ago, MtB said:

 

The forward surge caused by over-enthusiastic paddle-lifting would result in a boat hitting the gate with the lock near-empty, and with a good head of water still on the other side to oppose the thump. I'm more inclined to think it is deliberate ramming of the gate by a short boat in a full lock. The only reason I can think of to do this would be to try to open it, possibly before a level has been quite reached. 

 

Well two reasons really. The other being a deliberate intention to cause damage.

So it is a top gate?

[MtB]

11 minutes ago, Tracy D'arth said:

So it is a top gate?

 

Yes. Top gate.

 

 

[PaulJ]

15 minutes ago, MtB said:

 

The forward surge caused by over-enthusiastic paddle-lifting would result in a boat hitting the gate with the lock near-empty, and with a good head of water still on the other side to oppose the thump. I'm more inclined to think it is deliberate ramming of the gate by a short boat in a full lock. The only reason I can think of to do this would be to try to open it, possibly before a level has been quite reached. 

 

Well two reasons really. The other being a deliberate intention to cause damage.

You may well be right. Cant remember that lock being slow to fill though so not sure why anyone would do that (unless of course the lower paddles were still up)

Ive seen a good few bounce off the gates enough to let a good splurge of water in -and wondered at the forces on the collar that cant move unlike the opposite side.

[magnetman]

2 hours ago, alias said:

Reopened at 12.45.

 

It's raining and 40 boats waiting to go through, (with only one working bottom paddle at Broadmoor), so will probably wait until tomorrow.

 

40? 

 

[alias]

53 minutes ago, magnetman said:

 

40? 

 

 

That was the number being bandied about in the Red Lion at lunchtime.  I didn't count them myself, however the heavy two way traffic past the moorings is only just abating after four hours.