Thoughts on the Llangollen

[Keeping Up]

While travelling up the Llangollen canal I've noticed that when going upstream through the narrow tunnels the boat always tries to skew across with the stern against the left-hand brick wall. Looking ahead and behind me yesterday I could see that the boat ahead of me and the both behind me had both adopted the sime diagonal attitude. I wondered, is this purely an effect of the prop rotation or is it caused by the shape of the tunnel with a curved brick wall on the left and a flat towpath wall on the right? Thougts anybody?

 

 

As an aside I noticed that the aqueduct's name is spelt "Pontycysylltau" (with an extra Y in the middle and an AU instead of an E on the end) on the old photos that are used on the place-mats in the Telford Inn. I'd not seen that spelling before.

[Paul Evans]

It is some time since I was on the Llangollen and I don't recall what you describe, tho' I'm sure it happens. It is probably caused by the combination of the significant down stream flow on the canal (which is greater through tunnels and bridge holes), prop rotation and the tendency for boats to be slowed down through tunnels. I suspect that, if you have a clear run and the willingness to up your revs rather than reduce them, it might be possible to get through without slewing.

[cotswoldsman]

I presume you are heading towards Llangollen. It will be different coming back. It is caused by water coming down the Llangollen.

[Keeping Up]

I presume you are heading towards Llangollen. It will be different coming back. It is caused by water coming down the Llangollen.

 

That wouldn't explain why it is always with the stern to the left and the bow to the right.

 

Opening the throttle wider just seems to make the problem worse. If I did ever managed to get set straight up the middle, or even diagonally the other way, I couldn't hold it there for long and always ended up with the stern against the left wall. I'll have to try opening up wide when going downstream and seeing which side it goes then.

 

Another interesting effect I've noticed in the past is in the narrow concrete sections above Trevor, where if you go slowly the current pushes the boat towards the inside of the bends but if you go quickly the boat's momentum takes you to the outside of the bends. By adjusting the speed carefully you can get the boat to stay precisely in the middle as it takes the corner, and sometimes even to take the bend all by itself without having to be steered.

[RLWP]

<snip>

 

As an aside I noticed that the aqueduct's name is spelt "Pontycysylltau" (with an extra Y in the middle and an AU instead of an E on the end) on the old photos that are used on the place-mats in the Telford Inn. I'd not seen that spelling before.

 

It's a modern cheat, isn't it? U being pronounced ee in Welsh

 

Richard

[cotswoldsman]

That wouldn't explain why it is always with the stern to the left and the bow to the right.

 

 

 

Ummmm

[dor]

The spelling of Pontcysyllte is, like many welsh place names, quite variable on older maps and prints. This sometimes results from anglisisation, but often because words were written down phonetically by different people in different ways and it is only recently that they have become (almost) standardised.

[Tiny]

For the last many years our boat has been close to the wall at the backend of Ellesmere tunnel going upstream. It is quite dangerous we think as sometimes ripples in the water make the angle change quickly and the cabin top can bash the wall. The (new) wood at the tunnel entrance (put up when the entrance brickwork was smashed to pieces over a number of years) shows the damage to the wood over a short period that this can do. Of course the boats doing it (and maybe their crew members will have suffered damage here too. Likewise in the tunnel the damage is very apparent to the brick walls.

 

Of course the tunnel was designed for horse boats and no flow of water so the original design was OK but today, with BWs first priority on the canal being moving the 11 million gallons per day down the canal to forfill their contract with the water company - a contract that contains penalty clauses for none delivery, the conditions in the tunnel are totally different and more like riding the rapids at times - if a fast moving downstream boat arrives at the far end of the tunnel and, seeing us in it, slams on the anchors releasing a soliton.

 

With this in mind for many years we suggested to BW that under boater health and safety that they fix the problem by putting in a balk of timber just above water level on the wall side to stop boats swinging across and hitting the wall. The response has always been one of ... no money or we will look into it or even we see no problem. Yet at some lift bridges - which were in the same unit under the previous BW setup this timber balk to stop boat hitting the offside (raised bridge) was employed and suffers little damage as boats run along rather than hit it.

 

But, while BW won't spend on wood for this real safety feature they are happy to spend a fortune on safety fences round the Llangollen weir streams, on steps only for their men to use (one understands the H&S of BW employees is always reported on by the chairman of BW at meetings with directors) and even to replace Defra rash where they can't be bothered to repair something.

 

BW managers - whatever they say - rarely put the customer first. Especially if he is a boater.

 

The spelling of Pontcysyllte is, like many welsh place names, quite variable on older maps and prints. This sometimes results from anglisisation, but often because words were written down phonetically by different people in different ways and it is only recently that they have become (almost) standardised.

 

Living near the border we find it safest to ask a local how you pronounce a word. Mind you often two locals will pronounce it differently.

 

The place we live in is pronounced differently by different locals of long standing with the y being really prounounced a but it often gets to be an i though its never a u in our case. As for the next bit of the name that gets pronounced one way by the people our side of the border and a different way if you are a proper Welsh speaker from the right bit of Wales as opposed to the English bits of Wales down south.

[nb Innisfree]

One regular boater on the Langy has fixed a wheel on the front left hand side of his roof so that he can run it along the tunnel wall, this allows him to steer normally, also quite handy in other tunnels to protect your cratch.

[muddywaters]

While travelling up the Llangollen canal I've noticed that when going upstream through the narrow tunnels the boat always tries to skew across with the stern against the left-hand brick wall. Looking ahead and behind me yesterday I could see that the boat ahead of me and the both behind me had both adopted the sime diagonal attitude. I wondered, is this purely an effect of the prop rotation or is it caused by the shape of the tunnel with a curved brick wall on the left and a flat towpath wall on the right? Thougts anybody?

 

 

As an aside I noticed that the aqueduct's name is spelt "Pontycysylltau" (with an extra Y in the middle and an AU instead of an E on the end) on the old photos that are used on the place-mats in the Telford Inn. I'd not seen that spelling before.

We must have been the exception then because when travelling towards Llangollen last year the bow was against the left and stern the right.

Was more noticeable going across the Pontcysyllte (used the spelling from the pearsons guide lol) which we crossed 4 times twice with the flow and twice without.

Oh BTW did you notice anything in the WhiteHouses tunnel just before the aqueduct, felt like there was something under the water but only felt any bumps against the flow, never happened in any other tunnel

[owenk]

We found the "getting pushed over to the left hand wall" thing very noticable.

 

One otehr daft question the canal from Pontcysyllte up to Llangollen had the apperance of going quite pronoucedly "uphill" presumably this was/is purely an optical illusion?

[Thewatchmaker]

'We found the "getting pushed over to the left hand wall" thing very noticable.'

 

Yes me too.

Always noticed that with boats I have had, you learn to compensate for it after having to repaint cabin sides a few times!

Edited June 29, 2011 by Thewatchmaker

[PhilR]

We must have been the exception then because when travelling towards Llangollen last year the bow was against the left and stern the right.

Was more noticeable going across the Pontcysyllte (used the spelling from the pearsons guide lol) which we crossed 4 times twice with the flow and twice without.

Oh BTW did you notice anything in the WhiteHouses tunnel just before the aqueduct, felt like there was something under the water but only felt any bumps against the flow, never happened in any other tunnel

 

Does your boat have a right-handed prop?

 

I am not certain, but I think the towpath through the tunnels is cantilevered over the water and resting on stone pillars. This would also account for a tendency for the bow to head towards the towpath, especially with a left-handed prop.

Edited June 29, 2011 by PhilR

[Neil@CanalVoyagers]

Don't forget that the towpaths in the tunnels as well as on the aqueducts have been built to allow water to flow under them. In the tunnels, the towpath sits on pillars and the flow continues underneath. I've always assumed that as the greater volume of flowing water is always to your right (under the towpath) when heading upstream, as soon as you try to displace that volume at a higher speed it 'pushes' you away.

 

Same sensation you feel when you are on a shallow canal and have to many revs on - the stern gets sucked into the shallower water.

[magpie patrick]

Don't forget that the towpaths in the tunnels as well as on the aqueducts have been built to allow water to flow under them. In the tunnels, the towpath sits on pillars and the flow continues underneath. I've always assumed that as the greater volume of flowing water is always to your right (under the towpath) when heading upstream, as soon as you try to displace that volume at a higher speed it 'pushes' you away.

 

Same sensation you feel when you are on a shallow canal and have to many revs on - the stern gets sucked into the shallower water.

 

This...

 

It's the Benoulli principle, because there is more water passing the boat on the towpath side than the non towpath side, the flow is faster, pulling the boat away from the towpath, I suspect those who found their stern pulled that way were attempting to conpensate, those who found the bow pulled away were not. Or possibly the other way round

[David Mack]

Don't forget that the towpaths in the tunnels as well as on the aqueducts have been built to allow water to flow under them. In the tunnels, the towpath sits on pillars and the flow continues underneath. I've always assumed that as the greater volume of flowing water is always to your right (under the towpath) when heading upstream, as soon as you try to displace that volume at a higher speed it 'pushes' you away.

 

Same sensation you feel when you are on a shallow canal and have to many revs on - the stern gets sucked into the shallower water.

 

Actually it would be the other way around.

 

If the towpath is (say) 3 ft wide with water below and the water channel is (say) 8 ft wide at towpath level, then as the boat moves forward the bow divides the water so that 4 ft worth goes to the offside and 7 ft worth to the towpath side. The space between hull side and edge of the channel (below water level) is 6 ins on the offside and 3 ft 6 ins on the towpath side, most of which is under the towpath, if the boat is central. So on the offisde you are pushing 4 ft worth of water through a gap of 6 ins and on the towpath side, 7 ft worth of water through 3 ft 6 ins. The speed of the water flowing backwards past the boat is therefore much higher on the offside (about 4 times as high on these figures). This higher speed cause much greater pressure drop on the offside (due to Bernoulli's principle), which will pull the stern to the offside.

 

The same principle, but with the water passing under the boat, is what sucks the stern down in shallow water.

 

David

[Keeping Up]

Don't forget that the towpaths in the tunnels as well as on the aqueducts have been built to allow water to flow under them. In the tunnels, the towpath sits on pillars and the flow continues underneath. I've always assumed that as the greater volume of flowing water is always to your right (under the towpath) when heading upstream, as soon as you try to displace that volume at a higher speed it 'pushes' you away.

 

Same sensation you feel when you are on a shallow canal and have to many revs on - the stern gets sucked into the shallower water.

 

That would certainly explain it. I knew that the water flowed under the towpath on the aqueduct, but had assumed that it was solid ground beneath the towpaths in the tunnels.

[Keeping Up]

Coming back down through the tunnels I was able to open up the throttle and confirm that the stern was indeed sucked towards the offside wall, confirming that it is the water under the towpath which causes the effect. Knowing what to look for, I could easily see that the towpath is suspended on a series of arches, out from which the water flows as you pass.

 

So here's a follow-up thought; when travelling upstream, progress through the tunnels can be infuriatingly slow. Opening up the throttle produces a lot more noise, but how much does it really increase the speed? At times it feels as if the boat travels faster at lower revs.

Edited July 7, 2011 by Keeping Up

[Gibbo]

I've noticed the same effect going over the aqueduct (which I'm not going to try to spell).

[Rich]

It's a modern cheat, isn't it? U being pronounced ee in Welsh

 

Richard

and "au" pronounced "eye".

[journeyperson]

I came through the tunnels and over the aqueducts yesterday on my way up to Llangollen and the main thing I noticed was the strength of the flow against me which seemed stronger than usual, I practically came to a halt in Chirk Tunnel and I was following a boat over Pontcysyllte which did stop altogether. I wondered whether they were letting more water down at the moment although I have read that the flow is always constant. Leaves are beginning to affect progress too, particularly along the narrow, shallow stretch between Trevor and Llangollen.

 

 

[The Pipe]

I came through the tunnels and over the aqueducts yesterday on my way up to Llangollen and the main thing I noticed was the strength of the flow against me which seemed stronger than usual, I practically came to a halt in Chirk Tunnel and I was following a boat over Pontcysyllte which did stop altogether. I wondered whether they were letting more water down at the moment although I have read that the flow is always constant. Leaves are beginning to affect progress too, particularly along the narrow, shallow stretch between Trevor and Llangollen.

If your behind him you are "taking his water" if you have a big prop and draft to go wiyh it you could stop him maybe even pull him back!

[system 4-50]

One regular boater on the Langy has fixed a wheel on the front left hand side of his roof so that he can run it along the tunnel wall, this allows him to steer normally, also quite handy in other tunnels to protect your cratch.

Any chance of a piccy? I'd like to copy that idea !

[The Pipe]

Any chance of a piccy? I'd like to copy that idea !

Have a look at the old Bridgewater tunnel tugs they had wheels on the side. Might be better to have them on the bottom...................

[Pretty Funked Up]

I noticed the same thing going upstream in the tunnels etc. Bow right, stern left. I spent a good few hours thinking about it as we travelled. Came to the conclusion its the down stream flow but the direction of skew was equal opportunity. Mine went that way because my head subconciously steered away from the wall.

As the boat slows right down the nose sorta lifts up and wants to go one way or the other as its pushed by the flow, which your trying ya best to split neatly in the middle.

 

Once a boat in front has skewed their prop wash will help persuade yours to skew the same way as they have.

 

hope that makes sense

Edited September 20, 2011 by Pretty Funked Up