B&W double-headed GMAMs

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John Ashworth
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B&W double-headed GMAMs

Post by John Ashworth »

Nice B&W shot described as "Two GMAM with just 800 tons (max load)" - no date or location given.

https://scontent-b-dfw.xx.fbcdn.net/hph ... 9946_n.jpg

Did GMAMs only haul 800 tons? That seems very little. The East African Class 59 regularly hauled 1,000 tons uphill from Mombasa (sea level) to Nairobi (nearly 1,800 metres) with a single locomotive.
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Steve Appleton
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Re: B&W double-headed GMAMs

Post by Steve Appleton »

The GMAM had a rated tractive effort at 75% boiler pressure of some 60000 lbs, roughly twice that of a class 19D so, in theory, each GMAM could haul twice that of a 19D. But, of course that is not the only consideration. As we at FOTR only know too well, the track route geometry plays a huge factor. We limit our 19D to just under 300 tonnes out of Cullinan because of the 1:50 gradient starting immediately after the station and which includes a double reverse curve ('S' bend) with radii of about 150 metres each. But then we are being perhaps a tad sympathetic to our old iron lady and pandering to our volunteer drivers and firemen! Oh, and mindful of the possibility of a mid-afternoon rainstorm in summer.

So far as I am aware, on the old SAR, it was customary not to include any auxiliary water tankers in the train mass compliation; each was simply regarded as an integral part of the locomotive. Nonetheless the water tankers do need to be hauled and an allowance of about 45 tonnes each must be figured into the total permitted train mass in some way.

What this says is that although the official train payload may have been some 800 tonnes, it would in reality, including the two water tankers, likely be nearer to 900 tonnes in this case.

That does not detract from John's loaded question (pun intended), with which I agree. 800 or even 900 tonnes still seems a some way from a technical maximum load for a double-headed GMAM combination despite the obviously tortuous route that the train is running on. On paper, using our 19D as a comparison, each GMAM should be able to haul some 600 tonnes or more on a tightly curved, steeply graded branch line. With no other factors at play the two locos should be able to haul around 1200 tonnes. OK, only about 30% more than the train in picture! I have no knowledge of the EAR's main line, but the main lines here in SA would certainly be much easier in curvature and gradient, thus permitting much higher train masses than on the branches.

If the caption's statement about being near maximum permitted train mass is correct, then maybe there is another reason for this train mass limitation that we know nothing of? Coupler forces, bridge restrictions, braking limitations, adhesion limitations if it is wet, etc?
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Steve Appleton
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Re: B&W double-headed GMAMs

Post by Steve Appleton »

And, BTW, a nice historic picture. B+W often suits railway photography better than colour.
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Chris Janisch
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Re: B&W double-headed GMAMs

Post by Chris Janisch »

This looks like the Greytown line with 1in33 uncompensated grades, so that was the max load there I think. It was regarded as one of the greatest shows on earth in steam-lovers' eyes...
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John Ashworth
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Re: B&W double-headed GMAMs

Post by John Ashworth »

From the Garratt Yahoo group:
It does look like City View, running downhill back to Maritzburg.
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Martin Coombs
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Re: B&W double-headed GMAMs

Post by Martin Coombs »

As I mentioned on the Garratts Yahoo group, this pic does indeed look like it was taken at City View on the Greytown line out of Pietermaritzburg, with a 'dubbelkop' returning down the grade.

The ruling gradient on this line was 1 in 33 to 1 in 30, and may well have been uncompensated for curvature as Chris states. There were long banks at this steepness too, several miles at a time. A single 'gammat' was permitted to take 500 tons, and two of them could haul 800, for the SAR rules were that a double header was limited to 1.6x the single load. This was presumably because the two locos would not always be working perfectly together. Nevertheless it was worth doing in order to get the traffic through each section. When thinking critically about loads permitted, do also remember, as I said on the Yahoo group, that these were GMAs, not GMAMs, with the baffles added in tank and bunker to reduce the capacity and thus keep the axle-loadings down.

Up at the top end of the line the traffic was mostly timber, and sugar cane to Jaagbaan mill. Nearer to Maritzburg, however, the loads were more mixed. The Greytown locos were sub-shedded from Masons Mill, staying out for a week or two between boiler washouts. Change-overs were half way up the line, at Schroeders, with occasional locos running right through after a change of crew in order to get to or from Greytown. There was also a daily 'wayside' goods picking up and setting down wagons absolutely everywhere. This was hauled by a GF, for Greytown normally had 3 GFs in addition to around 8 GMAs, one for the daily Mount Alida branch timber train, one for the yard shunt, and the third for the 'wayside'.

Martin Coombs (Greytown fireman, on relief from Sydenham during 1974)
Brendon Anderson
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Re: B&W double-headed GMAMs

Post by Brendon Anderson »

Looks like those locos are working upgrade, just look at the exhaust from the stacks. If the location is indeed City View then the train is heading away from Pmb towards Alberts Falls and Greytown.
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Martin Coombs
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Re: B&W double-headed GMAMs

Post by Martin Coombs »

Brendon Anderson wrote:Looks like those locos are working upgrade, just look at the exhaust from the stacks. If the location is indeed City View then the train is heading away from Pmb towards Alberts Falls and Greytown.
Sorry, yes you are right. I have checked my old pics from 1974 and the halt is on the first right hand curve (going uphill) before the big left hand loop and then the steep climb up the side of the hill. Apologies. I only worked on the top end from Schroeders up to Greytown.

Martin
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