Pete, the Selkirks were not "passenger locomotives" in the sense that the
Hudsons were. They didn't have the limitations in freight service that affected
most steam engines designed specifically for passenger service (i.e. slippery
on heavy tonnage.) Selkirks were designed to pull both freight and passenger
trains in the mountains only. Thus they were intended as "general service" or
"dual service" engines and as mountain engines from the start. The
characteristics of CP's main line from Calgary to Revelstoke were such that
high speed was not not an option so a dual service engine was not the
compromise it might have been in other services.
In considering CP's decision to use the 2-10-4 rather than an articulated, it
is important to recall that the Challenger type wasn't developed until the
1930s. So it wasn't available for them to adopt. CP's mechanical staff were
certainly aware of developments in the field and perhaps could have designed an
articulated appropriate for their line if that had seemed the best for their
lines and traffic conditions. In this context it is important to remember that
CP's conditions were different from UP's. CP had a twisting, steep, slow line
through the mountains. UP's was straighter, faster and not as steep. The
Challengers were able to pull trains over UP's grades in Wyoming but could also
work east and west of their along the main line. CP built an engine that was
specialized for their more demanding grades, (and which were poorly configured
to handle general traffic at higher speeds on the prairies where they were
exiled in the 1950s).
The Selkirk as a logical improvement on the S1 2-10-2s of the 5800 series,
which in turn had been an improvement on the R class 2-10-0s of the 5700s,
themselves descended or rebuilt from 0-6-6-0s. Consistent with their motive
power policy generally, CP usually built moderately large engines rather than
giants for any given service. While CP had heavy traffic demands at various
times of year in different parts of the system, they didn't have consistently
heavy traffic to justify really big engines. It was easier to design a few
types of standard engines to handle average traffic and transfer extra power to
handle the peak power, than it was to have additional special types for heavy
traffic and move all of them around the system to handle the surges (and move
lighter ones in the opposite direction to compensate). The mountains were in
part an exception to this practice because they could justify heavier,
non-standard engines all the time. This worked precisely because they were
needed all the time, not just at peak periods. Other engines types could be
brought in to help with the extras. The 2-10-2s were built when the traffic
became too heavy for 2-10-0s, and the Selkirks similarly when the 2-10-2s were
no longer adequate. Each type was considered appropriate for the amount of
traffic it was typically required to handle, not for the peaks. If CP had
thought that larger articulateds were required for for normal traffic, they
would undoubtedly have ordered some.
If a Challenger or other articulated had been appropriate for CP's traffic, I'm
not sure that it would have required heavier rail. Axle load is what matters to
rail, and articulateds spread their weight over more wheels. They can also be
easier on the track structure especially on curves since they don't have such
long rigid frames. Turntables would probably have had to be enlarged at least
at Alyth, Field and Revelstoke, and some roundhouse stalls extended.
In theory, articulateds could have enhanced CP's goal of motive power
flexibility if their design allowed for higher speed running on the prairies
when mountain traffic was lower. All else being equal, they could have done
this more easily than the Selkirks because they wouldn't have been burdened
with the heavy counterbalancing and rigidity of a ten-coupled engine which
shook the engine and pounded the track. However articulateds would have been
overpowered for the prairie traffic and hence inefficient. Using them with full
tonnage would have required delays to traffic to permit enough cars to
accumulate. Some sidings would not have been long enough to accommodate trains
they could pull, as later proved to be a problem when CP tried using two Train
Masters on through freights.
When the Selkirks were built, CP apparently felt that it had provided enough
power, as the experiment with the 8000 was intended to improve efficiency
rather than increase power. Had they needed more power they would have sought a
larger locomotive. They could read the technical journals and visit other
railroads and builders. The fact that they had no personal experience with
articulateds (or remembered them only as very primitive) would not have stopped
them if they needed a more powerful engine.
Omer Lavallee, in "Canadian Pacific Steam Locomotives", outlines CP's motive
power policy of using a large number of small to medium engines as the backbone
of its fleet.
Don Thomas
----- Original Message -----
From: cripete <pjboylanboylan@xxxxxxxxxxxx>
Date: Tuesday, April 7, 2009 7:23 am
Subject: [cpsig] Selkirks and Other: Steam loco types
To: cpsig@xxxxxxxxxxxxxxx
In the case of the Selkirks they are distinctive
in that they were the only ten coupled passenger
locos built to serve on this continent(i.e.
excluding multi-engined articulated and duplex
locos). They were, like the first 4-8-2s designed
to haul passenger and express through the mountains,
without assistance. They also were an alternative
to articulated freight power in the Rockies and
Coastal Range, for moving manifests or drags.
Curvature, and rail weight, as well as gradients
played a role in the decision to use these 2-10-4s.
Canadian Pacific had very limited experience with
mallets. Those they had were compounds, of unsuperheated
designs, sans: arches, lateral motion devices, and any
device invented in the twentieth century.
They represented old technology, and were built with
inadequate steaming capacity.
High performance articulateds were extant at the
time when the Selkirks were built, so it is not
readily apparent as to why they were not used.
Most likely, the root cause was that economic conditions
prevented strengthening the right of way with
heavier rail, and even the expense entailed with
changing turntables and shop facilities were too
burdensome to justify, as an example ,
4-6-6-4 Challengers.
