South African Class NG G11 2-6-0+0-6-2

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South African Class NG G11 2-6-0+0-6-2
NGG11 54 at Chelsea 3 Apr 1990.jpg
NG G11 no. 54 "Solly" at Chelsea on 3 April 1990
Type and origin
Power type Steam
Designer Beyer, Peacock and Company
Builder Beyer, Peacock and Company
Serial number 5975-5977, 6199-6200 [1]
Model Class NG G11
Build date 1919-1925
Total produced 5
Specifications
Configuration 2-6-0+0-6-2 "Double Mogul" Garratt
Gauge 2 ft (610 mm) narrow gauge
Leading wheel
diameter
21 in (533 mm)
Driver diameter 30 in (762 mm)
Wheelbase Total:
51-53: 39 ft (11.887 m)
54-55: 39 ft 9 in (12.116 m)
Engines:
5 ft 9 in (1.753 m) coupled
10 ft 3 in (3.124 m) total
Length 51-53: 44 ft 7.5 in (13.602 m)
54-55: 45 ft 5 in (13.843 m)
Height 10 ft 4 in (3.150 m)
Frame Plate frame. Between pivot centres:
51-53: 22 ft (6.706 m)
54-55: 22 ft 9 in (6.934 m)
Axle load 51-53:
6.1875 long tons (6.3 t) on 5th driver
54-55:
6.675 long tons (6.8 t) on 2nd driver
Weight on drivers 51-53: 36.1375 long tons (36.7 t)
54-55: 38.9 long tons (39.5 t)
Locomotive weight 51-53: 44.9 long tons (45.6 t)
54-55: 48.2375 long tons (49.0 t)
Fuel type Coal
Fuel capacity 2 12 long tons (2.5 t)
Water capacity 970 imp gal (4,400 l) front
380 imp gal (1,700 l) rear
Boiler 4 ft 2 in (1.270 m) inside diameter
9 ft 3.625 in (2.835 m) inside length
5 ft 3 in (1.600 m) pitch
Boiler pressure 180 psi (1,240 kPa)
Firegrate area 51-53: 19.3 sq ft (1.793 m2)
54-55: 19.5 sq ft (1.812 m2)
Heating surface:
– Tubes
51-53:
211 tubes 1.75 in (44.4 mm) diameter
899 sq ft (83.520 m2)
54-55:
115 tubes 1.75 in (44.4 mm) diameter
13 tubes 5.5 in (140 mm) diameter
660.9 sq ft (61.400 m2)
– Firebox 51-53: 81 sq ft (7.525 m2)
54-55: 80.6 sq ft (7.488 m2)
– Total 51-53: 980 sq ft (91.045 m2)
54-55: 741.5 sq ft (68.888 m2)
Superheater area 51-53: Not superheated
54-55: 141.5 sq ft (13.146 m2)
Cylinders Four
Cylinder size 10.5 in (267 mm) bore
16 in (406 mm) stroke
Valve gear Walschaerts
Performance figures
Tractive effort 15,876 lbf (71 kN) at 75% pressure
Career
Operator(s) South African Railways [2][3]
Class Class NG G11
Number in class 5
Number(s) 51-55
Delivered 1919-1925
First run 1919
Withdrawn 1962
Preserved 1
Restored 2011
Current owner Sandstone Heritage Trust[4]

The South African Class NG G11 2-6-0+0-6-2 of 1919 is a South African steam locomotive from the South African Railways era.

Between 1919 and 1925 the South African Railways placed five Class NG G11 Garratt articulated steam locomotives with a 2-6-0+0-6-2 Double Mogul type wheel arrangement in service on the Avontuur narrow gauge line through the Langkloof and also in Natal. They were the first Garratt locomotives to enter service in South Africa.[5][6][4]

Background[edit]

The challenges of Africa resulted in the regular need for double-heading of steam locomotives on heavy trains. While West Africa found its solution in larger 4-6-2 Pacific and 2-8-2 Mikado locomotives at the beginning of the twentieth century, the steeper gradients and tighter curves in South Africa made a different solution necessary.[4]

On South African Railways (SAR) narrow gauge lines that solution was found in 1914 when orders were placed with Beyer, Peacock and Company for a narrow gauge Garratt locomotive which was to become the first Garratt to enter SAR service.[4]

Garratt characteristics[edit]

A powerful steam locomotive is problematic on a track gauge of only 2 feet (610 millimetres) and a tight minimum radius of about 150 feet (46 metres), which in practice restricts powerful rigid-frame locomotives to four-coupled driving wheels, often with at least one flangeless driving wheel set.[7]

The same problem also existed on Cape gauge single line light rail track, where train lengths would be limited because conventional locomotives had been enlarged to the limit of their possible power due to restrictions on axle loading. Alternative solutions would either be double-heading longer trains or re-building and re-laying large parts of the lines to accommodate heavier locomotives. Either method was expensive and in such conditions the Garratt design had distinct advantages.[7]

Garratt advantages[edit]

A Garratt is actually two separate locomotives combined in a double articulated format, thereby providing multiple powered axles over which the total locomotive weight is spread. This in turn results in a more powerful locomotive, since a much larger percentage of the locomotive’s total mass contributes to traction, compared to a tender locomotive of similar total mass.[7]

Unlike tender locomotives, Garratts are bi-directional, which eliminates the need for turntables or triangles, also known as wyes. The fact that they did not need to be run through to terminals to be turned around also made increased operational flexibility possible.[8]

Probably the greatest advantage of the Garratt was the fact that, with its boiler and grate area suspended between two engine units without the need to leave room for driving wheels and cylinders, wide and deep fireboxes with large grate areas and large diameter boilers were possible. On a Garratt the boiler could literally be dimensioned up to the full cross section of the loading gauge. With each set of cylinders and drivers constituting a separate engine, the end result was two locomotives in one with one huge boiler that needed only one crew. A Garratt is therefore a single locomotive with double the tractive effort and, with its weight distributed over a long and flexible multi-axle wheelbase, a lower axle loading.[7][9]

Garratt drawbacks[edit]

The Garratt design has some inherent drawbacks, however, the first being a diminishing factor of adhesion over long distances. As water and coal is consumed, the weight over the drivers is reduced, thereby reducing their factor of adhesion, the ratio of weight on drivers to tractive effort. Therefore, as the weight on the drivers decreases, the locomotive has less adhesion and becomes increasingly prone to slipping.[5][6]

With Cape gauge Garratts this was usually overcome by the use of auxiliary water tankers behind the locomotives, which enabled the onboard water tanks to remain filled longer and hence kept the factor of adhesion high farther.[5][6][10]

Another drawback is the risk of tilting. These narrow gauge Garratts had boilers of 4 feet 2 inches (1.270 metres) diameter on a frame width of about 6 feet 10.5 inches (2.096 metres). This created the risk of the locomotive tilting over on tight curves.[6]

Manufacturer[edit]

Although they had already been ordered in 1914, production was disrupted by the Great War and Beyer, Peacock and Company was only able to deliver the first three locomotives in 1919, after cessation of hostilities. All three, numbered in the range from NG51 to NG53, were erected at Uitenhage and put on trials on the Avontuur line in May 1920. These three locomotives were not superheated. They had outside plate frames, Walschaerts valve gear, Belpaire fireboxes and used saturated steam and slide valves.[5]

Having been proved successful during trials, another two locomotives were ordered from Beyer, Peacock. Numbers NG54 and NG55 were delivered in 1925 and entered service in Natal. These two were superheated and as a result had longer smokeboxes and were 9.5 inches (241 millimetres) longer in overall length. Superheating also required alteration of the valve gear and piston valves were therefore used instead of slide valves. The cabs of the second order locomotives were also improved to offer better protection to the crew.[5][6]

Classification[edit]

The system of grouping narrow gauge locomotives into classes was only adopted by the SAR somewhere between 1928 and 1930 and at that point these Garratt locomotives were classified as Class NG G11, with the letters "NG" indicating narrow gauge and the "G" prefixing the classification number identifying it as a Garratt locomotive.[2][5]

Service[edit]

Brass bilingual plate
English only plate

The first three locomotives were placed in service on the Avontuur line, but were all soon transferred to Natal where all but one remained for the rest of their service lives, until withdrawal by 1962. Number NG51 was later returned to the Avontuur line to replace the retiring Class NG3 number NG5 as yard shunter at Humewood Road.[5]

The two locomotives of the second order also served in Natal, ending up working on the branch from Estcourt to Weenen by 1966, when they were both transferred to the Avontuur line in exchange for two newer Class NG G13 locomotives. There they were employed on yard duty and on transfer trips to and from the docks until, after the arrival of the Class 91-000 diesel-electric locomotives in 1973, they were withdrawn from service in October 1974.[5][6]

Preservation[edit]

Of the first three locomotives, only number NG52 still exists. It was sold to Rustenburg Platinum Mines in 1956 and became their number 7. After retirement at the mine, it was preserved at the Museum of Man and Science in Johannesburg in 1974, then moved to the Klein Jukskei Motor Museum by 1981 and finally donated to the South African National Railway And Steam Museum (SANRASM). In 2010 it was acquired by Sandstone Estates and by 2011 it was being restored and rebuilt in Bloemfontein.[4] The other two were scrapped after being retired from SAR service.[11]

The two superheated locomotives still exist. Although number NG54 was restored in Bloemfontein in 1989, it was staged out of service at Humewood Road until it was removed by Sandstone Estates in 2011 to be restored once again. Number NG55 was restored to full working order and was being run on the Patons Country Narrow Gauge Railway (PCNGR) at Ixopo in Natal by 2005. At the time the PCNGR was operating tourist excursion trains between Ixopo and Ncalu.[6][12]

Features illustrated[edit]

The main picture and the following photographs illustrate views of the Class NG G11 locomotive from different sides and in different liveries.

See also[edit]

References[edit]

  1. ^ Hamilton, Gavin N., The Garratt Locomotive - Garratt Locomotives produced by Beyer, Peacock, retrieved 10 November 2012 
  2. ^ a b South African Railways and Harbours Narrow Gauge Locomotive Diagram Book, 2’0” Gauge, S.A.R. Mechanical Dept. Drawing Office, Pretoria, 28 November 1932
  3. ^ South African Railways and Harbours Locomotive Diagram Book, 2’0” & 3’6” Gauge Steam Locomotives, 15 August 1941, as amended
  4. ^ a b c d e Sandstone Steam Railroad
  5. ^ a b c d e f g h Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. pp. 105–106. ISBN 0869772112. 
  6. ^ a b c d e f g Durrant, A E (1989). Twilight of South African Steam (1st ed.). Newton Abbott, London: David & Charles. p. 123. ISBN 0715386387. 
  7. ^ a b c d Beyer, Peacock Garratt Locomotives
  8. ^ Advantages of the Garratt concept
  9. ^ Technology in Australia 1788-1988
  10. ^ Disadvantages of the Garratt concept
  11. ^ Middleton, John N. (2002). Railways of Southern Africa Locomotive Guide - 2002 (as amended by Combined Amendment List 4, January 2009) (2nd, Dec 2002 ed.). Herts, England: Beyer-Garratt Publications. 
  12. ^ SAR Class NG G11 55 (2-6-0+0-6-2)