Current and Proposed New-Builds

A screenshot from one of their recent YouTube videos. I believe it is the boiler and outer firebox, though with a few bits missing.


Posted on their Facebook page a few weeks ago.

 

Good lord what a size! Like almost everything else in the U.S it`s big. Thanks a lot for posting this impressive picture!

Knut

 

The size of that tender...
I wonder if any of the condensing/re-use systems could ever have been got to operation at that scale. You've got 73 tonnes of water to play with

 

They’re close to finishing the mammoth boiler, and are getting ready to start funding for the frames.

 

Looking forward to seeing this in the headshunt at Wooten

 

Plenty big enough, just look at the SAR 25C .... and while we're about it, why not add the electrically operated Cossart valve gear from the Algerian express passenger Garratts?

Methinks the T1 team have got a fair bit to be getting on with for now! From what I've read of the originals, it'll be extremely interesting to follow the details when it comes time to set up the suspension. If that makes no sense, treat yourself to a good read through their website.

 

If you look at the side on photo, the front of the boiler is actually above the middle set of wheels on the trailer - everything to the left is the smokebox and streamlining. The barrel is only 18' long. The grate is 11'6" long! 92 square feet - an A1 or Duchess are 50 sq ft. Firebox and combustion chamber are about 18' long by the looks of things.

 

Are those weights just the locomotive?
It looks like the average axle loading of the T1 is 20% higher than the Big Boy. Is that correct?

 

Interesting use of the word 'only' there!

 

The T1 had 502,200 lb locomotive weight, the rest being the tender.
Of that, 279.910 was on the driving wheels. 122.720 on the trailing truck and 99.570 on the front truck.
Weights fairly similar to a Big Boy, which has 545.000 on the drivers, 99,800 on the front truck and 127.200 on the trailing truck.

 

For the weight of the engine it ought to be able to maintain a power output what exactly? Given that the design dates to 1942 we should be looking at a little under 9,000 hp but the design is credited with 6,500 hp. Something is not quite right here.

Do not misunderstand me. Any new build is a bold and worthy venture but for a locomotive weight in excess of 224 tons the power to weight ratio is well below the standards obtained many years before the first of this class was constructed.

 

I don't get this direct translation that weight should be proportional to power.

Do a couple of thought experiments. Imagine you built a loco, and then built an exact analogue, equivalent in all respects except it was double the linear size. Weight is related to volume, and in volume terms it is eight times larger. But power depends on boiler dimensions, and in critical areas - grate area, heating surface - scale as area, so they have gone up four times. So comparing the two, weight has gone up eight times but power four times: the power to weight ratio has halved.

That's a bit of a reductio ad absurdum, but consider a more nuanced version. Imagine an Atlantic built out to the limits of loading gauge - boiler as wide and high as it can get, cylinders the biggest that will fit. Now stretch it into a pacific - the new loco is undoubtedly heavier, but where does any extra power come from? If you consider the power is related to input, i.e. the rate you can burn coal, then in this hypothetical design you haven't changed that, the grate area is the same. If you consider the power is related to output, then you haven't changed that either, because the cylinders on the Atlantic were already at their limit. So the pacific is bigger, but not inherently more powerful. Potentially what it does have, by virtue of a longer boiler (and therefore higher hot water volume), is a greater reserve of steam in a bigger boiler, so could run at beyond it steady state power "mortgaging the boiler" for a few minutes longer; it may also be a bit more sure-footed. But it isn't necessarily more powerful, while it is inherently heavier.

In reality, loco design is more subtle than that. Designers got adept at squeezing ever more out: half an inch of cylinder diameter here, 20psi extra boiler pressure there. But I think it is naive to think that there is some magic formula that directly equates weight and power. Even if it is possible to create a 100 ton, 4,000hp loco, that does not automatically mean that a 200 ton, 8,000hp loco is possible, certainly not within the same constraints of width and height.

Tom

 

It must indeed be more complex than either constant power-to-weight regardless of size or a square/cube law. It could be interesting to see what happens in the other direction, on 15 inch lines such as the RHDR with locos that are more or less scale models of full size locos.

 

If we look at 15" gauge BVR No 9 was improved enormously compared with Number 7 and 8, the ZB article is readily accessible, the level of improvement did not involve any great increase in locomotive weight.

Getting back to the T1, the strengths and weaknesses of US steam were identified many years ago though there has been some work carried out since. The US locomotives were admired for their robust mechanical design but the thermodynamic side was felt to leave something to be desired. And if Andre Chapelon indicates to you that your engines could be improved, as a locomotive engineer you might well be advised to take notice.

US railroads did make some peculiar purchasing decisions, locomotives for heavy freight work with no high speed requirement were obtained with driving wheels more suited for mixed traffic service, some would argue passenger service. Then you have locomotives which are unable to make use of their tractive effort and power output because they are carried on too many undriven axles.

If we look at the results of IMLEC the efficiency of steam locomotives in their model engineering scale is not high, the 2021 competition winner managed 2.238%. 15" gauge is seen as a good compromise for development work (see Nigel Day).
On metre gauge you can equal or surpass not only the best UK standard gauge but also the best standard gauge types to be found in many other countries. Want a 5,000 hp 2-10-0 on metre gauge? There is a design for you. If you need more power on this gauge this can be achieved. Need a 6,000 hp design for standard gauge? Weighing 146.4 metric tons? That design exists too. So what are the limits concerning what might be achieved?

 

Mind you there's an argument that the UK loading gauge is metre gauge stock running on standard gauge track...

 

Certainly 3'-6". Several MkII carriages found their way to New Zealand.

 

I’ve been on them - I think probably my most recent trip in a Mark II.

Tom

 

We do not need a new Star class 4-6-0. Period.

 

Don't sit on the fence, tell us what you really think!!
Pat

 

Sorry I'm late to the controversial news. Seems the GWS and the 4709 group have you lot divided.

I may not make any sense, but...
I really don't think using a Castle's no. 8 boiler on a 47xx chassis is a good idea. PERIOD.

The GWS really thinks that using 7027's boiler for a Night Owl, and the frames for a new Star is a great idea, but to me, its freaking idiotic.

First, the 4709 group, bless them, hasn't wrapped around their heads the thought that their locomotive will not fit today's loading gauge on the mainline,

Second, the no. 8 boiler, on a 2-8-0's frames, will not clear any bridges, making the engine too big for most heritage railways,

Third, and most importantly, we already HAVE a Star: 4003 "Lode Star"

and Fourth, they really need to step up on fundraising, if they originally wanted to raise the estimated 800,000 quid needed for a new no. 7 boiler.

All I can really say is that the GWS and the 4709 Group have both made themselves look bad with the decision, and I personally think that sacrificing 7027 for another pie-in-the-sky scheme makes the new-build circuit look bad too.

Now don't get me wrong, I personally love the new-build engines (60163, 45551, 2999, 6880, 1014, 3840, 82045, 72010, 32424, 2007, 61673, etc...), but when you sacrifice a Barry-condition wreck that could be restored, for aanother extinct Great Western locomotive, and, especially snatch it from a group who was restoring it, is just plain wrong.

Now I’ll shut up and watch the comments…