DB HTE Class 66s

[Adrian Barr]

Do you know what a "56 ton" coupling actually means in terms of force it can take?

To be honest, no. My naïve assumption is that you could hang a 56 ton weight off it without damaging the coupling, with that being translated into the forces exerted by pulling a train. It's a bit like brake force - a class 66 has a brake force of 68, but 68 what? Brake force units? Clearly there's some calculation behind both brake force and coupling strength values, but that's about as much as I know without a technical or engineering background.

I think the article you linked relates to this document, the 2022 RSSB paper "Guidance on the Limits of Freight Train Trailing Length as Governed by Coupler Strength."
https://aether-uk.com/CMSPages/GetFile.aspx?guid=510ef60b-ae91-48a5-9782-a320c1563d03

It talks about the concept of "traction load" in a way that suggests my understanding is not completely daft:

Traction load is the maximum load that can be sustained by the screw coupling; it can be likened to the safe working load (SWL) of cranes or lifting equipment.

Normally, the maximum weights in the loads books for different coupling strengths only take into account the trailing weight of the train and the characteristics of a particular route - factoring in the pulling power of the locos adds another complicating factor!

 

[slugsix]

Thanks for that. That makes sense - to a point. I'd love to know the detailed engineering reasons for this. Do you know what a "56 ton" coupling actually means in terms of force it can take? These locos with wheelcreep - even including 66/0s are able to exert tractive effort forces of around 100,000 lbf, and so two of them would be around 200,000 lbf. The quoted max TE figure for a 66/6 is 105000 lbf. So two of them would be 210000 lbf. That's 93.75 tons at the drawbar between inside loco and leading wagon. That's way over 56 tons, and if you are on a steep gradient, you'll also have the gravity induced forces acting the other way - for a 1 in 100, a 4000 ton train would generate 40 tons of pull due to the gradient. So we're nearly up to 150 tons now before we even start working with snatches.

Incidentally, I found this article, which states that some 34.5t and 56t couplings have been "uprated" to 40t and 63t respectively.

Coupler research paves way for longer freight trains

UK: The length and capacity of freight trains is to be increased as a result of research which has found that existing wagon couplers can safely accommodate higher trailing loads without upgrading or a detailed engineering assessment. The research by the Rail Safety & Standards Board ...

www.railwaygazette.com

OK. So I understand it a bit better now. These ratings are the maximum continuous force that can be exerted without permenantley deforming the coupling. They are NOT the maximum traction force that can be exerted through it. For example, from the BR document MT19, a coupling with a traction rating of 56t has a proof rating of 71t and a minimum breaking load of 122t. These are the screw type couplings, not the automatic (swinghead) couplings. Obviously, maximum loads are derived from this sort of stuff. So it would seem that, for whatever reason, DB has simply chosen "not to go there", while FL have, enabling them to run massive trains from the Mendips with various combinations of 66/5, 66/6 and 59 in multi.The current rail industry standard RIS-2780-RST Iss 1.1 applies and also SD001 issue 2.

So, I would agree, it would seem that whilst there is no real reason why DBs 66/6 can't operate in multi, DB has chosen not to allow them to do so, thereby saving cost administrative tasks for something which, at the moment they do not need.

 

[hwl]

OK. So I understand it a bit better now. These ratings are the maximum continuous force that can be exerted without permanently deforming the coupling. They are NOT the maximum traction force that can be exerted through it. For example, from the BR document MT19, a coupling with a traction rating of 56t has a proof rating of 71t and a minimum breaking load of 122t. These are the screw type couplings, not the automatic (swinghead) couplings. Obviously, maximum loads are derived from this sort of stuff. So it would seem that, for whatever reason, DB has simply chosen "not to go there", while FL have, enabling them to run massive trains from the Mendips with various combinations of 66/5, 66/6 and 59 in multi. The current rail industry standard RIS-2780-RST Iss 1.1 applies and also SD001 issue 2.

So, I would agree, it would seem that whilst there is no real reason why DBs 66/6 can't operate in multi, DB has chosen not to allow them to do so, thereby saving cost administrative tasks for something which, at the moment they do not need.

The sectional trailing load limits are a mess for double heading but this is being addressed by NR.

The 63(.5)tonne couplers aren't in MT19 (1967) but are on lots of locos (all the modern ones) and most wagons (e.g. those new in the last 20 years). Getting the paperwork properly sorted for those substantially helps double heading.

To be honest, no. My naïve assumption is that you could hang a 56 ton weight off it without damaging the coupling, with that being translated into the forces exerted by pulling a train. It's a bit like brake force - a class 66 has a brake force of 68, but 68 what? Brake force units? Clearly there's some calculation behind both brake force and coupling strength values, but that's about as much as I know without a technical or engineering background.

I think the article you linked relates to this document, the 2022 RSSB paper "Guidance on the Limits of Freight Train Trailing Length as Governed by Coupler Strength."
https://aether-uk.com/CMSPages/GetFile.aspx?guid=510ef60b-ae91-48a5-9782-a320c1563d03

It talks about the concept of "traction load" in a way that suggests my understanding is not completely daft:



Normally, the maximum weights in the loads books for different coupling strengths only take into account the trailing weight of the train and the characteristics of a particular route - factoring in the pulling power of the locos adds another complicating factor!

Tonnes force
e.g. 56 tonne coupler is rated for 56t * 9.8065 = 549kN on the level

There are two limits coupler and traction, the lower of the two applies. In the 66 case for a single 66 the loco TE is the issue, for two locos the coupler strength is the issue below ~20-25mph

Brake force - can be tonnes or lambda the units need to be stated (tonnes force or % of vehicle weight) and this causes frequent confusion as this is often mis-united

 

[slugsix]

The sectional trailing load limits are a mess for double heading but this is being addressed by NR.

The 63(.5)tonne couplers aren't in MT19 (1967) but are on lots of locos (all the modern ones) and most wagons (e.g. those new in the last 20 years). Getting the paperwork properly sorted for those substantially helps double heading.


Tonnes force
e.g. 56 tonne coupler is rated for 56t * 9.8065 = 549kN on the level

There are two limits coupler and traction, the lower of the two applies. In the 66 case for a single 66 the loco TE is the issue, for two locos the coupler strength is the issue below ~20-25mph

Brake force - can be tonnes or lambda the units need to be stated (tonnes force or % of vehicle weight) and this causes frequent confusion as this is often mis-united

Interesting. Thanks for that.

Yes, I've read stuff about NR updating the "loads book" and app. It's being addressed.

The 56 ton coupler is in MT19. However, recent research has shown that these couplings, in some cases, can be uprated to 63t - that's the article I linked. The full research paper is available on the RSSB site. I'd say that the rating of the coupling ISN'T the maximum force that can be transmitted through the coupling. It's the maximum *continuous* force that can be transmitted without distorting it permanently. The evidence is simple. Two Class 66/0s can work the 6B13 tanks, and they do so regularly with 25 TEAs == 2500 tons on the back. 66/0s have a max TE of 92,000 lbf or 402kN. Double that and you get 184000lbf (82 tons force or 804 kN) - and that's before you have a gradient force pulling the other way to add to it. Clunderwen bank is 1 in 82 so that gives a gradient force of ~31 tons from the wagons. So you've got 31 tons pulling one way on the front coupling of the leading wagon and 82 tons pulling the other for a total of 113 tons going through the coupling. Does that make sense, or is there something wrong there? (Other than the small loss as the 66s have to move themselves too...)

It seems there's no technical reason that prevents DBs 66/6s working in multi - it's just that DB are "playing safe" and staying clear of the subject - because it doesn't need to operate 2 x 66/6s - so why bother with costly ball ache.

 

[hwl]

Interesting. Thanks for that.

Yes, I've read stuff about NR updating the "loads book" and app. It's being addressed.

The 56 ton coupler is in MT19. However, recent research has shown that these couplings, in some cases, can be uprated to 63t - that's the article I linked.

Because there wasn't a 63t (1.5MN) option to chose from the 63t (1.5MN) couplings (used at 63t across Europe) were just labelled as 56t as no one wanted to sort it. It isn't an uprating as such just correctly labelling in the same way that already happens across most of the rest of Europe.

The full research paper is available on the RSSB site. I'd say that the rating of the coupling ISN'T the maximum force that can be transmitted through the coupling. It's the maximum *continuous* force that can be transmitted without distorting it permanently. The evidence is simple. Two Class 66/0s can work the 6B13 tanks, and they do so regularly with 25 TEAs == 2500 tons on the back. 66/0s have a max TE of 92,000 lbf or 402kN. Double that and you get 184000lbf (82 tons force or 804 kN) - and that's before you have a gradient force pulling the other way to add to it. Clunderwen bank is 1 in 82 so that gives a gradient force of ~31 tons from the wagons. So you've got 31 tons pulling one way on the front coupling of the leading wagon and 82 tons pulling the other for a total of 113 tons going through the coupling. Does that make sense, or is there something wrong there? (Other than the small loss as the 66s have to move themselves too...)

The wagon resistances. Have a look for the follow on T1302 on the RSSB site.

It seems there's no technical reason that prevents DBs 66/6s working in multi - it's just that DB are "playing safe" and staying clear of the subject - because it doesn't need to operate 2 x 66/6s - so why bother with costly ball ache.

The technical reasons are paper work and driver training :
a) paperwork - 56t gives you 549kN or 63t gives 617kN max traction load which is 68% or 76% of the max TE of 2x66 at low speed
b) ... hence the drivers need to be trained for starts to keep to N5 (56t) or N6 (63t) till at least 20mph then start tapering the notch upwards if they need (i.e. not reaching N8 below ~30mph) so as not to exceed the traction rating
c) with two locos if the brakes at the back haven't fully released the screw part of the coupler has a nasty habit of breaking even if you follow b)
d) the traction rating is designed/set to avoid fatigue issues which you do by keeping stress well below the yield levels.
e) you also want safety factors.

Modern continental locos allow you to limit the total TE (in multi) to the coupler traction rating making it easy not to do anything silly.

 

[slugsix]

Because there wasn't a 63t (1.5MN) option to chose from the 63t (1.5MN) couplings (used at 63t across Europe) were just labelled as 56t as no one wanted to sort it. It isn't an uprating as such just correctly labelling in the same way that already happens across most of the rest of Europe.

Yes, I understand that and agree.. They've essentially just redone the numbers. Properly. And that's resulted in a upping of the ratings now it's been done properly, From an operating point of view this brings cost benefits as per linked article.

The wagon resistances. Have a look for the follow on T1302 on the RSSB site.

Ta. I'll have a look at that - although I've spent a number of years in traction simulation so probably have more TE and resistance curves than I'd like to admit to. Wagon resistances add to the gradient resistance and add to the forces through the coupling. So that strengthens the evidence of the case I was making - which in turn leads to your list below....

The technical reasons are paper work and driver training :
a) paperwork - 56t gives you 549kN or 63t gives 617kN max traction load which is 68% or 76% of the max TE of 2x66 at low speed
b) ... hence the drivers need to be trained for starts to keep to N5 (56t) or N6 (63t) till at least 20mph then start tapering the notch upwards if they need (i.e. not reaching N8 below ~30mph) so as not to exceed the traction rating
c) with two locos if the brakes at the back haven't fully released the screw part of the coupler has a nasty habit of breaking even if you follow b)
d) the traction rating is designed/set to avoid fatigue issues which you do by keeping stress well below the yield levels.
e) you also want safety factors.

Modern continental locos allow you to limit the total TE (in multi) to the coupler traction rating making it easy not to do anything silly.

Yeah I get all that thanks. Clearly, if there's a decent business case, then it's possible - as per FL 66/6s on the Mendip trains. All these points follow on when you apply common sense to the mechanics. However, while really interesting, this is a moot point from the angle I was actually coming from. I could already see reasons why you wouldn't *want* to do it, but I was more asking to see if there were any actual technical reasons that meant you *couldn't* do it. The reason being I've been told by somebody that you can't do it because the DB 66/6s have "been regeared" and that they are very different to the FL 66/6s. I didn't share that view and so I was looking for evidence in that regard. As expected, I haven't found any.

Hope that makes sense, and thanks for your time in replying - it's very interesting stuff.

The technical reasons are paper work and driver training :
a) paperwork - 56t gives you 549kN or 63t gives 617kN max traction load which is 68% or 76% of the max TE of 2x66 at low speed
b) ... hence the drivers need to be trained for starts to keep to N5 (56t) or N6 (63t) till at least 20mph then start tapering the notch upwards if they need (i.e. not reaching N8 below ~30mph) so as not to exceed the traction rating
c) with two locos if the brakes at the back haven't fully released the screw part of the coupler has a nasty habit of breaking even if you follow b)
d) the traction rating is designed/set to avoid fatigue issues which you do by keeping stress well below the yield levels.
e) you also want safety factors.

Just another thought regarding this list. It would equally apply to the example of 2 x 66/0s on the B13 tanks wouldn't it - except that you've got slightly less max TE. Still plenty to bring in the above though....

 

[hwl]

Just another thought regarding this list. It would equally apply to the example of 2 x 66/0s on the B13 tanks wouldn't it - except that you've got slightly less max TE. Still plenty to bring in the above though....

The reasons not to as far as I can see:
a) change require a lot of effort (inc lots of paperwork) and DB aren't that enthusiastic about much at the moment
b) you need to give the drivers a very precise set of driving instructions (and have high confidence in all inputs to those calculations behind the instructions)
c) you need the drivers to stick to those instructions
d) they might be worried about finger pointing if things go wrong

 

[slugsix]

The reasons not to as far as I can see:
a) change require a lot of effort (inc lots of paperwork) and DB aren't that enthusiastic about much at the moment
b) you need to give the drivers a very precise set of driving instructions (and have high confidence in all inputs to those calculations behind the instructions)
c) you need the drivers to stick to those instructions
d) they might be worried about finger pointing if things go wrong

Absolutely. And if you think you don't need to do it, then why bother right? IMO, (c) is very difficult. You're slowing down on an upgrade. Notching back to provide less power is counterintuitive.

I've been thinking more about the 2 x 66/0 case overnight. All of your points apply there too. Of course the characteristics are different, but to what extent?

Many people think that the 66/6 is very different to the 66/0 tractive effort wise. In fact, when you consider the whole speed range it actually isn't -because for most of that range the limiting factor is the enginer power - which is 3200 hp. Providing full engine power is available (see below), then power at the rail becomes fairly constant - usually somewhere around the 80% mark due to efficiency losses through the transmission etc. So for a 3200hp loco, RHP will be roughly 2600hp. It will of course vary a little as the control system is varied to balance the engine and electrical load. However, for practical purposes, knowing the rail horsepower (RHP) of 2600, you can now calculate the TE for any given speed PROVIDING full power is available. The equation is TE = (375 * RHP) / MPH (TE in lbf). So for MOST of the speed range, the tractive effort produced at a given speed will be close to identical for 66/0 and 66/6. However, there are "issues" at the top and bottom of the speed range...

Lower gearing ONLY gives you significantly higher TE at the very bottom of the speed range. The TE that can be delivered to the rails is always limited by the lower of what the specific adhesion allows and what the traction equipment allows. Eventually, these limits are no longer a factor and full engine power is available to be transmitted to the rails. Providing there is good adhesion, then it's the electrical equipment that dictates this point. Once 66/0 and 66/6 have both reached this point, where full engine power is available, then their TE at a given speed will be roughly equal.

At the top end of the speed range there comes a point where the power unit is unable to provide enough power to overcome the reverse current being generated by the motors. This is often referred to as the unloading point. From this point, full power is no longer available at the rail, and starts to decrease with increased speed. Due to its lower gearing, this unloading point will come at a lower speed for a 66/6. From this point on, the 66/0 will have higher TE for any given speed. This is why the 66/6 has a lower maximum speed than the 66/0.

With that knowledge, if we now go back to the issues of couplings, we can see all the issues apply for any combination of locomotives. When talking about 66/0 and 66/6, the only differences relevant come at the bottom of the speed range. Since full power is available on both 66/0 and 66/6 well below the speeds you quoted (20 - 30mph), then clearly, the issues you've raised apply to 2 x 66/0 as well. To the point where you could possibly argue that making 66/6 a special case with regards to multiple working almost doesn't make sense. It feels too complicated and costly to bother. Which takes us back to the Mendip 66/6s. Do they have special instructions for drivers, or are the couplings simply just strong enough?

 

[Wyrleybart]

Brake force - can be tonnes or lambda the units need to be stated (tonnes force or % of vehicle weight) and this causes frequent confusion as this is often mis-united

Brake force in this discussion is a bit misleading.
It is a matrix of factors which are computed to deliver a number. When I started in TOPS in 1980 the TOPS computer worked it out and gave you a train list with the parameters on it. The list might print something like "may have sufficient brake force to run class X". This means TOPS has checked the speeds, weights, brake force etc and the train performance might be improved. Back in the early 1980s this might mean that 7M76 timed to run at up to 45mph might have all wagons able to run at 60mph and therefore could be run as 6M76. The brake force however was calculated on the vehicles input, and it was incumbent on the train preparer to confirm that all the brakes worked and the brake force was as computed on the list.

 

[Rail Quest]

Whilst its been discussed previously, DB have now confirmed the program is being expanded to 15 locomotives in total all the way up to 66665. I've amended the table as thus. The article linked below outlines some more details about locomotives earmarked for conversion:

66659 (ex-66171) is the latest to be converted, with 66161/172/181 identified as likely to be the three next in line.

DB Cargo has added 66155/165/197 into the WBHT pool for the ‘66/6s’, which will take the conversion programme up to 66665.

Source: https://www.railmagazine.com/news/fleet/2025/02/25/db-cargo-s-full-class-66/6-conversions-identified
[Link directs to Rail Magazine article confirming DB expansion of Class 66/6 programme]

 

[31160]

It would be nice to get up to 66666 just because it would look good

 

[Class15]

It would be nice to get up to 66666 just because it would look good

Hahaha yes that would be amazing!

 

[Rail Quest]

It would be nice to get up to 66666 just because it would look good

Yeah was thinking that! DB could add fire vinyls and name it 'The Devil' haha

 

[Tinsley 1976]

66659 is hanging round south wales area done the 6R72 today

 

[Trainman40083]

66660 worked 0E23 from Toton to Doncaster a today.

 

[Western 52]

66659 is hanging round south wales area done the 6R72 today

It's just passed Pembrey and Burry Port on the 6B41 1145 Westerleigh to Robeston oil empties, a train that rarely runs.

 

[Adrian Barr]

66660 worked 0E23 from Toton to Doncaster a today.

After that test run on the 4th March (ran back to Toton as 0M22), 66660 worked a 6T32 ballast from Toton to Barnsley on the 5th (returning the following morning), 6E02 coil empties to Boston + 6M07 loads to Wolverhampton on the 7th, 6E03 empties from Wolverhampton to Toton on the 8th, then light engine to Bescot to work a 6P01 weekend ballast in the Worcester area last night / today.

66660 seen here at Ancaster with Friday's 6E02: https://www.flickr.com/photos/129016838@N03/54371711022/ (Photo: Trevor Wallis)

Also found this shot of it inside Toton in December, before repainting and renumbering: https://www.flickr.com/photos/66001/54229679067/ (Photo: the mother '66' 66001)

 

[TonyW66]

Whilst its been discussed previously, DB have now confirmed the program is being expanded to 15 locomotives in total all the way up to 66665. I've amended the table as thus. The article linked below outlines some more details about locomotives earmarked for conversion:


Source: https://www.railmagazine.com/news/fleet/2025/02/25/db-cargo-s-full-class-66/6-conversions-identified
[Link directs to Rail Magazine article confirming DB expansion of Class 66/6 programme]

I understand 66 659 is ex. 66 161 and not 66 171 ? Although it is not uncommon for locos to be swapped out or the order changed, there is confusing 'gen' as to which one has actually been converted. Pip Dunn's article shows this too, saying 171 was converted to 659, but later contradicts that by saying 161 was the 9th loco converted, making it 659. Any update would be appreciated including the former identity of 66 660.

 

[DBS92042]

I understand 66 659 is ex. 66 161 and not 66 171 ? Although it is not uncommon for locos to be swapped out or the order changed, there is confusing 'gen' as to which one has actually been converted. Pip Dunn's article shows this too, saying 171 was converted to 659, but later contradicts that by saying 161 was the 9th loco converted, making it 659. Any update would be appreciated including the former identity of 66 660.

66659 is ex-66171
66660 is ex-66161

They can be distinguished as 171 had a hole in its air dam at one end (which 161 didn't have) and 659 has this hole while 660 doesn't

 

[JKF]

Portbury-Margam steel traffic has been a fairly reliable turn for the HTE locos this month. Of the 31 workings so far in April, 28 have been HTE 66s. Only 653, 657 and 658 have been absent, the latter two having never been on this traffic and seemingly working out of the midlands.

 

[99009]

The 66's which were allocated on TOPS to become 66661 - 66665 no longer are and reverted back to the standard DB 66 TOPS pool last month. This suggests that further conversions beyond the current 10 locos have been cancelled or delayed.