Why the huge variety of diesel locomotives when first introduced?

[Bevan Price]

On the diesel side 47s and 50s are really second generation designs, coming along some years later than the original Type 4 (i.e. 2000HP +) designs of Classes 40 and 44/45/46, 56s were even later.

The power capability of the later designs was simply not possible prior to about 1962 and neither operators or politicians were prepared to wait that long. It might have been possible to get GM locos, but (according to an explanation I've seen from someone who was involved at a fairly high level) GM were insisting on all production being in the USA and payment being in US$ hard cash. The UK was in a fairly parlous state for foreign exchange at the time and the Treasury would not permit such a transaction.

Much of the multiplication of classes came from updated power units coming along (e.g. Cl 26/27) but some came from UK manufacturers who wanted a showcase for their products and managed to convince the politicians that BR should provide same, despite the objections of the engineers.In general the latter group were the less successful designs.

Yes, I think there was almost certainly some "political" interference to ensure diesel orders went to a range of loco. builders.

 

[70014IronDuke]

Whilst the Western still liked to think it was still an independent GWR, there was some merit in trying diesel hydraulics. A Class 42 weighed 79 tons, and had a slightly better power output than a Class 40 weighing 133 tons. So, in principle, the Class 42 could haul heavier loads than a Class 40. And the 42 was based on a successful German design (V200 / DB Class 220). The big mistake was letting NB build the similar (but unreliable) Class 43.

But, as a small, non-standard class, they were sacrificed when spare class 47s became available following the post Marples-Beeching cuts.

The Westerns (Class 55) were about 15 tons lighter than a Class 47, but also non-standard, and lacked an economical way to allow modification to operate electric train heating. Coupled with arrival of HSTs, and more spare 47s available, Class 55 was also sacrificed after rather short lives.

ITYM Cl 52s (of course). But the fitters on BR(W) I talked to did not like the Cl 52s, they were very cramped. I suspect expensive to maintain.

It must be very difficult to assess now, but my bet for the worst Type 1 would be the D84xx - Cl 16 (I had to look it up). I think the fact that there were only 10 locos, and always at Devons Rd or Stratford, allowed them to escape much notice. Would be interesting to see their availability and miles per casualty figures.

 

[Spartacus]

Whilst the Western still liked to think it was still an independent GWR, there was some merit in trying diesel hydraulics. A Class 42 weighed 79 tons, and had a slightly better power output than a Class 40 weighing 133 tons. So, in principle, the Class 42 could haul heavier loads than a Class 40. And the 42 was based on a successful German design (V200 / DB Class 220). The big mistake was letting NB build the similar (but unreliable) Class 43.

But, as a small, non-standard class, they were sacrificed when spare class 47s became available following the post Marples-Beeching cuts.

The Westerns (Class 55) were about 15 tons lighter than a Class 47, but also non-standard, and lacked an economical way to allow modification to operate electric train heating. Coupled with arrival of HSTs, and more spare 47s available, Class 55 was also sacrificed after rather short lives.

Westerns were class 52, Deltics were 55, but the big weight difference between diesel electric and diesel hydraulic was due to engine and construction differences: most diesel electrics used low speed engines, which were much heavier than the high speed ones normally used on diesel hydraulics: a notable exception being the Class 55 Deltic which was lighter than the closest comparable, but still less powerful, hydraulic loco the Western.

This made them more suitable to further weight reduction by using new construction methods, lightweight alloys, stressed skin and load bearing body sides. A good illustration is the difference between the NB Class 41 and Class 43 Warships, the former built using traditional construction methods, which were a full 37 tons heavier than the later ones built in the more familiar style, and only 16 tonnes lighter than the bigger (and notoriously heavy) Class 40.

 

[70014IronDuke]

If Class 20s were always to be used in pairs then it would have been cheaper and simpler to build half as many of a locomotive with twice the power and a cab at each end (a class 40?!).

Once it became obvious they were the most reliable design available, BR ordered enough to meet its entire anticipated requirement for Type 1s,

Not as I understand it. BR ordered a load of Class 20s, but also went ahead with the totally untried D85xx, and ordered - I forget, 100 plus such locos.

AIRI, EE closed the production line down for Cl 20s, but then had to reopen it when BR ordered the last batch - which included those numbered in the D83xx range, delivered in late 66 or 67, IIRC.

but this was only a rational decision if they were expected to be used singly. Therefore visibility from the cab couldn't have been seen as a problem at the time, which is perhaps explained by the fact that there were still plenty of steam locos around at the time with visibility that wasn't much better. There's perhaps also the weight factor helping with braking on unfitted freights, but even those were declining rapidly before the 20s were much out of their first decade. How much was the almost universal nose-to-nose pairing the result of concerns about visibility, and how much because most of the duties that would suit a single class 20 disappeared soon after they were ordered?

But there were plenty of single Cl 20 turns, eg on colliery branches in the early 1970s. At least, that's how I remember it, around Toton.

 

[70014IronDuke]

From memory, I think that Class 15 was nowhere near as unreliable as Classes 16 & 17. Their main problem was that most of their work disappeared due to Marples-Beeching, and what little work remained could be performed by other classes. As a relatively small class, it was more economic to get rid of them and retain Class 20 of which there were over 200, and which was a pretty reliable loco.

"Pretty reliable" ? - I think the Class 20 must be in the running for the most reliable loco - bar the 08 - of the lot. (It helped that they never had train-heat boilers, of course.)

 

[87015]

"Pretty reliable" ? - I think the Class 20 must be in the running for the most reliable loco - bar the 08 - of the lot. (It helped that they never had train-heat boilers, of course.)

Don't know about that. Known as bombs for a reason, going around in pairs probably helped the perception but hardly unbreakable!!

 

[MarkyT]

"Pretty reliable" ? - I think the Class 20 must be in the running for the most reliable loco - bar the 08 - of the lot. (It helped that they never had train-heat boilers, of course.)

The electrical wiring of the vanilla ones, not those retrofitted for creep speed 'merry go round' operations, was remarkable simple, fitting entirely on a single drawing I managed to print legibly on a sheet of A3. When a group I was part of first acquired loco 20110 from scrap merchants for the South Devon Railway in the early 1990s, we had to fit and wire up a number of missing components in the control equipment. It was a much easier task than I had imagined.

Simplicity and reliability was a hallmark of many EE products both for domestic and export applications. 50+ year old class 37s, still working on the main line here, gained an impressive 'spanner' award very recently.