[N&W] Garratts vs. Mallets

[nw-mailing-list at nwhs.org]

 >[Richard Hood writes:]
 >
 >Something for the engineers out there to ponder, why did the N&W not try a
 >Garratt design?  The Garratt is technically superior to the Mallet.  It has
 >a large deep firebox which goes down to rail level, a short but large
 >diameter boiler providing excellent steaming capability, coal and water
 >carried over the driving wheels for better traction, two pivots providing
 >better tracking of tight curves, bi-directional travel, therefore no
 >turntables or wyes required.  Railways that tried both in Africa and
 >Australia generally preferred Garratts.  UP started a design for a Garratt
 >which would have knocked the spots of a "Big Boy", but I think diesels had
 >already made their mark.  Despite the above I think the Y6b and A take some
 >beating for looks.
 >
 >Regards, Richard Hood
 >

Richard - I can think of several reasons why they didn't try a Garratt.
First, your assumption that the Garratt is superior to the Mallet is based
on what, besides the configuration of the firebox and boiler and the
bi-directional capabilities?  Here are some points to ponder:  1) no
railroad off these shores operated a Garratt in the weight and power class
of US Mallet and Mallet-derived locomotives (I. E. simple articulateds) -
Garratts were satisfactory enough on roads with tight curvature and light
rail and bridges, because they spread the weight over a longer distance -
this overbalanced some of the other objections I list below; 2) US Mallets
and simple articulateds in their last stages of development used boiler
pressures of up to 300 pounds, a figure not approached by any Garratt that I
know of  - only one set of flexible joints was necessary for any Mallet-type
locomotive, and Garratts would require at least two sets; 3) the long steam
pipes to the cylinders would have presented extreme condensation and
pressure loss problems (were any Garratts operated in extremely low
temperatures?), especially the longer distance between the smokebox end of
the boiler and the cylinders on the other end - N&W's Bob Pilcher was
concerned about the pressure loss to the front engine of the A, a very small
distance compared to any to be considered on a Garrett; 4) while it's true
that all the weight of the fuel and water supply of the Garratt was
available for adhesion, this weight would diminish as these supplies were
consumed, so the tonnage rating of the locomotive would also diminish - a
Garratt starting out with full tonnage at the bottom of the mountain would
become more slippery the farther up the mountain he went - a solution would
be to limit tonnage, not a satisfactory answer; 5) compounding in a Garratt
would have caused extreme condensation problems, as the exhaust from the
high-pressure cylinders, way out on one end of the thing, would have to be
carried all the way to the other extreme end for use in the low-pressure
engine - an answer to this would be turning the engines around so that the
cylinders would be close to the boiler, but that might introduce tracking
problems.  Remember, N&W's Y-6 was the equal of Big Boy at 25MPH, using a
boiler roughly the size of that of the J; this was because of the efficient
use of compounding, a principle that everybody else had given up on - partly
furthered, I'm sure, by the desire of the commercial locomotive builders to
sell their produce.  6) a small point, but the patents on Mallets had
expired long ago but Garratts would still have to be built under license.
Is there hard evidence that UP started the design of a Garrett, or is that a
rumor?  And what were the characteristics of the proposal that would have
made it "knock the spots" of a Big Boy?  And, last of all - was any
locomotive builder in the UK pushing locomotives of the Mallet pattern?  If
no one was trying to sell Mallets and Garratt was pushing its design, might
that fact alone have resulted in some sales?   And no railroad operating
Garratts anywhere in the countries you mention faced the task of moving the
tonnages they'd have had to deal with in the US.
Now, understand, Richard.  I never had to deal with the question of "should
I buy Garratts or Mallets for my railroad"; like you, I'm dealing with the
question with the benefit of fifty years of hindsight.
But I have listed several of the reasons why I think Garratts were not used
here.

EdKing