Are/Will the class 769s be suitable for the North Downs Line?

[Fincra5]

319's weren't underpowered more than capable of dealing with the gradient coming out City Thameslink and before they had OTMDRs fitted spirited drivers could easily get well over a 100 out of them on MML. I would accept they were sluggish off the mark and do wonder whether that was because they didn't want to overstress the power electronics from that era. Whats not disclosed with 769's is what the TE curve is when running on the diesel alternator sets but given the two engines together will only deliver 780kW at the output shaft of the engine that will be further reduced at the rectified output of the alternator to less than 750kw I would suggest. So nominally only 75% the rated power of the motors is available but doesn't mean it can't handle the gradients on the NDL just that SRT's will be longer which is why the schedules have been slackened already.

I was thinking this! Look how steep the gradients are in the TL "Core" yet 319s managed it, sure a bit less weight, but they'll manage 1 in 100!

 

[AM9]

I was thinking this! Look how steep the gradients are in the TL "Core" yet 319s managed it, sure a bit less weight, but they'll manage 1 in 100!

The fact is that 769s now manage inclines in Lancashire and South Wales much steeper than 1:100, (actually the NDL ruling gradient is 1:96):

Wigan Wallgate to Crows Nest Junction has stretches of 1:56 within a long stretch of 1:100 'ish. That doesn't seem to stop the Northern service there.​

On the Rhymney line, there is a nearly 3 miles of climb ranging from 1:74 to 1:85 including a standing start at Heath High Level station (1:80) and Llanishen station (1:74), see here: Which has also been largely fixed for TfW.​

Neither of those lines are in particularly dry parts of the country either.

 

[Nicholas Lewis]

The fact is that 769s now manage inclines in Lancashire and South Wales much steeper than 1:100, (actually the NDL ruling gradient is 1:96):

Wigan Wallgate to Crows Nest Junction has stretches of 1:56 within a long stretch of 1:100 'ish. That doesn't seem to stop the Northern service there.​

On the Rhymney line, there is a nearly 3 miles of climb ranging from 1:74 to 1:85 including a standing start at Heath High Level station (1:80) and Llanishen station (1:74), see here: Which has also been largely fixed for TfW.​

Neither of those lines are in particularly dry parts of the country either.

Indeed the units will work perfectly well on the NDL as long as engines are reliable which they ought to be as they've been used in hundreds of units built by Alstom some in plenty of hot countries. Of course if there are issues with the cab layout then thats probably game over as its unlikely the cab can be redesigned in any meaningful way.

 

[Fincra5]

The fact is that 769s now manage inclines in Lancashire and South Wales much steeper than 1:100, (actually the NDL ruling gradient is 1:96):

Wigan Wallgate to Crows Nest Junction has stretches of 1:56 within a long stretch of 1:100 'ish. That doesn't seem to stop the Northern service there.​

On the Rhymney line, there is a nearly 3 miles of climb ranging from 1:74 to 1:85 including a standing start at Heath High Level station (1:80) and Llanishen station (1:74), see here: Which has also been largely fixed for TfW.​

Neither of those lines are in particularly dry parts of the country either.

Exactly!

 

[Deepgreen]

20 m tall trees lining the route make an insignificant contribution to the rail adhesion issues relative to the topography. The major cause is the difference in elevation between the top of the North Downs (consistently in the range 200 m - 220 m above Ordnance Datum in the 11 miles from Guildford to Dorking) and the railway (max elevation east of Gomshall at 100 m above Ordnance Datum).

So you are claiming that leaf fall from the heavily-wooded surroundings of the railway are insignificant? I would say that the ruling gradient of 1 in 96 in, say, tree-less prairies, would present few adhesion problems, but through woodlands it does. You seem also to be stating that the 'valley effect' of moist air pooling on the railway is the most significant factor - it isn't, because number of calm, clear nights required for it is very small and it would only affect early morning trains on those few days anyway. Another factor is, of course, that the route isn't a true valley anyway - cool moist air is generally free to roll away to the south rather than sit on the railway.

== Doublepost prevention - post automatically merged: 10 Mar 2022 ==

I've not heard of that - they're just underpowered, as indeed 319s were to start with. Even a 319 on the wires is slower off the mark than say a Sprinter.

I think we're in danger of mixing up power and adhesion here. Nominal acceleration is limited by power available, and even over-powering without adequate adhesion is pointless.

 

[starlightEXPRESS]

So you are claiming that leaf fall from the heavily-wooded surroundings of the railway are insignificant? I would say that the ruling gradient of 1 in 96 in, say, tree-less prairies, would present few adhesion problems, but through woodlands it does. You seem also to be stating that the 'valley effect' of moist air pooling on the railway is the most significant factor - it isn't, because number of calm, clear nights required for it is very small and it would only affect early morning trains on those few days anyway. Another factor is, of course, that the route isn't a true valley anyway - cool moist air is generally free to roll away to the south rather than sit on the railway.

== Doublepost prevention - post automatically merged: 10 Mar 2022 ==

Leaf fall is significant, of course it is, but there are many places on the network with similar gradients and which are also tree-lined. This is obvious if you read posts from others - yes the NDL has steep gradients, but nothing exceptional - yes it has trees lining it (but actually there are long stretches that are pretty open) - again not exceptional.

What makes the NDL exceptional is the topography - the "valley effect" as you call it. Cold air settles on top of the North Downs and rolls down the scarp slope, where it mixes with a layer of warmer air, which is moisture-laden from the evaporation of water from the Wey, Mole and Tillingbourne. The effect is black ice forming on the rail lines, which causes the adhesion problems. The air cannot "roll away to the south" because of the Greensand Ridge (Leith Hill is the highest point in Surrey) so it trapped between the two parallel ranges of hills.

This "valley effect" takes place irrespective of the weather (unless there is a strong easterly or westerly wind) - it is not restricted to a few winter nights each year - this is basic physics. The base of the North Downs is well known as a "frost pocket" - you know this from living in Betchworth. The actual temperature recorded in Gomshall and neighbouring settlements is generally two or three degrees lower than that recorded at Wisley and Charlwood most daytimes. On winter days with a clear sky, the difference can be as much as five degrees.

So to summarise - yes leaves are a problem, yes gradients are a problem - but these characteristics are not unique to the NDL. The unique circumstances are the topography - which is the significant underlying cause of the adhesion problems on this stretch of line for the vast majority of the year.

 

[FenMan]

Leaf fall is significant, of course it is, but there are many places on the network with similar gradients and which are also tree-lined. This is obvious if you read posts from others - yes the NDL has steep gradients, but nothing exceptional - yes it has trees lining it (but actually there are long stretches that are pretty open) - again not exceptional.

What makes the NDL exceptional is the topography - the "valley effect" as you call it. Cold air settles on top of the North Downs and rolls down the scarp slope, where it mixes with a layer of warmer air, which is moisture-laden from the evaporation of water from the Wey, Mole and Tillingbourne. The effect is black ice forming on the rail lines, which causes the adhesion problems. The air cannot "roll away to the south" because of the Greensand Ridge (Leith Hill is the highest point in Surrey) so it trapped between the two parallel ranges of hills.

This "valley effect" takes place irrespective of the weather (unless there is a strong easterly or westerly wind) - it is not restricted to a few winter nights each year - this is basic physics. The base of the North Downs is well known as a "frost pocket" - you know this from living in Betchworth. The actual temperature recorded in Gomshall and neighbouring settlements is generally two or three degrees lower than that recorded at Wisley and Charlwood most daytimes. On winter days with a clear sky, the difference can be as much as five degrees.

So to summarise - yes leaves are a problem, yes gradients are a problem - but these characteristics are not unique to the NDL. The unique circumstances are the topography - which is the significant underlying cause of the adhesion problems on this stretch of line for the vast majority of the year.

Fair play for your explanation. Living elsewhere along the line, I'll believe the 769s can cut it when I'm on a decently loaded unit departing from Sandhurst towards Reading on a damp autumn morning.

The Turbos struggle, but is that because their undoubted power to clamber over the rise to Crowthorne is undermined by adhesion issues?

 

[Deepgreen]

Leaf fall is significant, of course it is, but there are many places on the network with similar gradients and which are also tree-lined. This is obvious if you read posts from others - yes the NDL has steep gradients, but nothing exceptional - yes it has trees lining it (but actually there are long stretches that are pretty open) - again not exceptional.

What makes the NDL exceptional is the topography - the "valley effect" as you call it. Cold air settles on top of the North Downs and rolls down the scarp slope, where it mixes with a layer of warmer air, which is moisture-laden from the evaporation of water from the Wey, Mole and Tillingbourne. The effect is black ice forming on the rail lines, which causes the adhesion problems. The air cannot "roll away to the south" because of the Greensand Ridge (Leith Hill is the highest point in Surrey) so it trapped between the two parallel ranges of hills.

This "valley effect" takes place irrespective of the weather (unless there is a strong easterly or westerly wind) - it is not restricted to a few winter nights each year - this is basic physics. The base of the North Downs is well known as a "frost pocket" - you know this from living in Betchworth. The actual temperature recorded in Gomshall and neighbouring settlements is generally two or three degrees lower than that recorded at Wisley and Charlwood most daytimes. On winter days with a clear sky, the difference can be as much as five degrees.

So to summarise - yes leaves are a problem, yes gradients are a problem - but these characteristics are not unique to the NDL. The unique circumstances are the topography - which is the significant underlying cause of the adhesion problems on this stretch of line for the vast majority of the year.

My point exactly - the conditions are far from unique to the NDL - so why (possibly) are the 769s having problems? BTW - Leith Hill, etc. are far enough away to allow a less dense settling of cool air than would be the case in a true, narrower valley. The topography is far from unique too, and I was talking about a significant valley effect as would be found on the relatively few clear calm nights. The tree-lined nature of much the route (even where open fields are nearby, the railway is often lined by mature trees) also restricts the formation of so-called black ice, and such ice on running rails should present little issue for adhesion - on conductor rails it's far more of a problem. I commuted on the route for years and iced running rails were simply not a problem - autumn leaf fall certainly was, however. The key issue is that, if true, the possible problems with the 769s must partly stem from added load to the unpowered bogies giving a greatly reduced adhesion, and, as such, the conversion was bound to suffer from very predictable problems. Of course, all this talk of power/adhesion issues may be rubbish and the units are performing fine, but the "basic physics" of the altered power/weight equation do not look good on paper.

 

[JN114]

so why (possibly) are the 769s having problems?

Simple - they aren’t. As asserted many times a working 769 has no issues with gradients on the line.

This whole sub-thread is borne out of a fiction passed off as mess room gossip.

 

[Clarence Yard]

Loaded (with sandbags) timing test runs have yet to be done to validate all the projected point to point times, so we shall see in due course.

Until then, any fears are just wibble.

 

[starlightEXPRESS]

BTW - Leith Hill, etc. are far enough away to allow a less dense settling of cool air than would be the case in a true, narrower valley. The topography is far from unique too, and I was talking about a significant valley effect as would be found on the relatively few clear calm nights.

Sorry, this is just wrong. I am not going to waste my time explaining this again.

== Doublepost prevention - post automatically merged: 11 Mar 2022 ==

Loaded (with sandbags) timing test runs have yet to be done to validate all the projected point to point times, so we shall see in due course.

What on earth have they been doing if they haven't done a simulated fully loaded test yet? Haven't they been doing tests runs for over 18 months already?

 

[Jturner98]

If the 769 introduction is going so badly I’m surprised the 185 units haven’t been looked at. Apparently the NDL has some large gradients which the 185 units could easily handle. That is of course when or if they are released from TPE

 

[JonathanH]

If the 769 introduction is going so badly I’m surprised the 185 units haven’t been looked at. Apparently the NDL has some large gradients which the 185 units could easily handle. That is of course when or if they are released from TPE

There is no need to even think about 185s. 185s haven't been released by TPE so aren't able to be looked at.

If the 769s don't work, the 165s stay where they are. No other fleet needs to be considered for LTV services at all. Discussion in this thread debunks any idea that the gradients on the NDL are anything particularly worthy of overpowered traction.

The question will then be what to do about west services but as already mentioned in this thread, as every day passes, it is one day nearer to 150s and 158s becoming available from other operators.

 

[FenMan]

If the 769 introduction is going so badly I’m surprised the 185 units haven’t been looked at. Apparently the NDL has some large gradients which the 185 units could easily handle. That is of course when or if they are released from TPE

You are speculating obviously, so probably one for Speculative Ideas.

That said, I'm not convinced if DfT or GWR would be interested in units that would reduce seating capacity by a third!

 

[geoffk]

There is no need to even think about 185s. 185s haven't been released by TPE so aren't able to be looked at.

If the 769s don't work, the 165s stay where they are. No other fleet needs to be considered for LTV services at all. Discussion in this thread debunks any idea that the gradients on the NDL are anything particularly worthy of overpowered traction.

The question will then be what to do about west services but as already mentioned in this thread, as every day passes, it is one day nearer to 150s and 158s becoming available from other operators.

What's the problem with 769 cabs (apart from lack of aircon, which can be retrofitted) which wasn't also a problem with the 319s on Thameslink?

 

[JonathanH]

What's the problem with 769 cabs (apart from lack of aircon, which can be retrofitted) which wasn't also a problem with the 319s on Thameslink?

Modern standards.

It is explained succinctly by a poster previously. While drivers of 769s on other routes work other units, the GWR 769s are going to be the primary workplace for the LTV drivers and so have to be appropriate based on 2022 standards, not 1988 ones.