I came across this project to restore these monster American locomotives which dated from the 1940s. In principle, they consist (since many survive as historic monuments) of two large locomotives with one boiler supplying the steam. What I do not understand is the rationale behind the immensely complicated design.
The same effect was achieved more simply by the Beyer-Garatt configuration, with two engine units and a boiler slung in between on a carrying frame. The space over the engine units was used for fuel and water. The boiler was set low down, giving the engines a low centre of gravity which made them suitable for high speed running. Large numbers of this type were built for use in Commonwealth countries and some narrow gauge (2ft) examples are running on the Welsh Highland Railway.
In principle, the Beyer-Garatt could be much larger than any that were every built; a double 2‑10‑2 would have been practicable, with no limitation to the size of the boiler. The puzzle is why, when faced with demands for more powerful locomotives, ALCO rejected, or did not consider, the Beyer-Garatt?
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Yes, I love both Mallets and Beyer Garrets. In my collection I have a Big Boy for no other reason than it looks fantastic!I may purchase the BR LMS Garrett for the same reason.
I take it for granted you know all the Pros and Cons of the Garrets from Wicky. My only thought is this bit in the 'Other designs section:
'The Garratt was, obviously, not alone in the field of articulated locomotives. Aside from the well-known Fairlie and Meyer types, the Garratt had contemporary and similarly-designed competition in the form of the Union-Garratt, Modified Fairlie and Golwé.
This bit:
'Of these, the closest was the Union-Garratt, a type originally conceived owing to the perceived necessity for a rigid connection between a bunker or tender and a firebox fed by a mechanical stoker. Though it could be argued that the NZR G class locomotives were Union-Garratts (having their bunkers mounted on the boiler frames, rather than on the hind engine unit)'
My thinking being here, in somewhat uninformed CME mode speculation. (1)Union Pacific already had Challengers as you know. So the Big Boy is no design problem as such (common parts to?). Also the Americans were commited to 'mechanical stokers' unlike us in BR. Perhaps UP never looked into this issue after 1920, even though Garret designers above, solved the problem. (2)Also, but I suspect it will not be the case, Union Pacific (+ ATSF +SP) hated any design that asked for more water of good quality (even as I write this I can feel surely South African railways, et al would have had the same problems?)
I think we need an American, NW or UPer to let us know. By 1939 USA things had moved on too in the UP.
Thinking of those who never liked Mallets, have you seen the PRR T1 project. They are using Tornado rebuilding costings for their estimates - x10!
As it happens I really do need a T1 :)
Best,
Mike W