NGG16

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NG151 at work in South Africa
For more detail see NGG16 on Wikipedia.

The NGG16s are the largest and amongst the most powerful steam locomotives ever built for 2 ft gauge and were originally designed for work on the South African Railways. The most extensive South African Railway 2 ft lines were Port Shepstone-Harding (120 kilometres/75 miles), Umzinto-Donnybrook (150 km/93 mi) and Port Elizabeth-Avontuur (280 km/174 mi). Not surprisingly, the motive power requirements were exacting and locomotives developed accordingly, to a size exceeded nowhere in the world.

The Welsh Highland Railway is now home to five members of this class, 87, 130, 138, 140 and 143. The latter three arrived in Wales in 1997, and are all from the same batch built by Beyer Peacock in 1958. 87, from an earlier batch, followed in 2006. 130 arrived in 2015.

History[edit]

Cockerill-built no. NG86, still inscribed NG/G13, c. 1937
Beyer, Peacock-built no. NG115, c. 1939
Beyer, Peacock-built no. NG128, the first with welded water and coal bunkers, c. 1951
Beyer, Peacock-built no. TC11 for Tsumeb Copper, possibly SAR no. NG142, c 1958
Hunslet-Taylor-built, possibly no. NG149, c. 1967

The NGG16 2-6-2+2-6-2T Beyer Garratts were a direct descendant of the successful Class NGG13 Garratts (initially, the first NGG16 batch was classified NGG13). Three different builders constructed the Class NGG16 locomotives in five batches. John Cockerill built numbers 85 to 88 in Belgium in 1937. Beyer Peacock & Co built 109 to 116 in 1939, 125 to 131 in 1951, and 137 to 143 in 1958, in Manchester. The last batch, 149 to 156, were built in South Africa by Hunslet-Taylor at Germiston in 1967/68. Number 156 has the distinction of been the last steam locomotive built for the SAR.

Whereas some of the earlier, smaller South African Garratt classes have not survived (NGG12s 2-6-2+2-6-2Ts of 1927, and the solitary NGG14 all were scrapped in 1952), the NGG16 class survived intact. They were shared between Natal and the Port Elizabeth-Avontour line until the latter was dieselised in 1973, when they were withdrawn (but not scrapped) or moved to Natal. With the gradual closure of the Natal 2ft lines, ending with the 1986 closure of Port Shepstone-Harding, the story could well have ended for the class too. Luckily that section was taken over by the Alfred County Railway Co and the use of Garratts continued.

With the ACR being committed to steam, a sub-class was created in 1989, when No 141 was rebuilt with Gas Producer Combustion and other improvements. With No 155, rebuilt in 1990, it forms Class NGG16A.

The closure of some 2 ft gauge lines in South Africa, together with the dieselisation of others, means that a considerable quantity of rolling stock and other material has come up for disposal there. The WHR has taken full advantage of this situation.

Principal dimensions[edit]

Length over couplers 48 feet 5 inches
Wheel arrangement 2-6-2 + 2-6-2T
Total wheelbase of loco 43' 3"
Coupled wheelbase of each power unit 6' 3"
Power unit wheelbase inc. trailing axles 13' 10.5"
Driving wheel diameter 2' 9"
Trailing wheel diameter 1' 9"
Total heating surface 1,049.1 square feet
Heating surface of tubes 859 sq. ft.
Heating surface of firebox 82.1 sq. ft.
Heating surface of superheater 149 sq. ft.
Grate area 19.5 sq. ft.
Boiler pressure 180 pounds per sq. inch
Cylinders (x 4) 12" diameter, 16" stroke
Valvegear Walschaert
Tractive effort @ 85% pressure 21,553 lb.
Water capacity 1,823 gallons
Weight in working order 62 tons (approx.)


Power comparisons[edit]

Before Garratts were introduced on the Port Elizabeth limestone trains in South Africa's Eastern Cape, the most powerful locos being used were Baldwin NG10 4-6-2s. These NG10s were permitted to haul a maximum of 150 tons up the winding 8 mile 1-in-40 bank from Loerie. In 1928 NGG13s were introduced and were permitted to haul 215 tons up the bank (the instructions in South African Railways 'Private Working Time Books' did not change for the NGG16s that were used later).

In their excellent booklet, 'Narrow Gauge Super Power - Limestone to Port Elizabeth', Leith Paxton and David Payling compare the limestone loads that the NGG16s hauled up the 8 mile 1-in-40 bank from Loerie with FR slate wagons and with current WHR coaching stock. In South Africa, the NGG16s would haul 8 loaded DZ Wagons (8 DZ-9s or 10 DZ-6s) and a brake van up the steep winding bank. The equivalent loads would be 77 loaded FR iron slate wagons or 25 present day WHR(C) coaches (before modest reduction to allow for the extra number of axles).

While the NGG16s on WHR could in theory haul these loads, this comparison does highlight their main drawback. The success of the design of the Garratts is the ability to create a powerful loco, with a big boiler and a relatively low axle weight, that can run on tightly curved lines. Ideal for South African narrow gauge applications, the Garratts were successful on dry rails, but they were not designed for the weather conditions of North Wales. So, in practice, the challenge in hauling 25 WHR cars up the bank from Dinas would not be in producing the required power but in getting that power onto the rails without slipping. In poor conditions, the NGG16s are prone to slipping on the WHR with the current loads of 6-7 cars.

Comparisons with other 2 ft gauge gauge articulated and semi-articulated locomotives are interesting but can be deceptive. Tractive effort calculations do not assess the locomotive's ability to raise the steam necessary, while, as noted above, units designed for a lighter axle load may be light footed. In addition, another key factor in operating would be the range of speed available, which with a geared locomotive in particular can be rather restricted:

NGG16 compared with some other 2 ft gauge articulated locomotive types
Locomotive Wheel Arrangement Tractive effort (85% boiler pressure)1 Axle Weight
NGG16 Garratt 2-6-2 + 2-6-2T 21,364 lb. 6.2 tons
Tasmanian Hagans J1 2-6-4-0T 20,558 lb. 7.7 tons
Shay Class B 4w+4wTG 16,802 lb. 7 tons
Avonside Hunslet 0-4-0+0-4-0TG 12,375 lb.2 6.5 tons
Bagnall (eg Monarch) 0-4-4-0T 12,140 lb. 7.1 tons
Pioneer Garratt K1 0-4-0 + 0-4-0T 11,500 lb.3 8.4 tons
Double Fairlie (David Lloyd George) 0-4-4-0T 9,639 lb. 6.75 tons
Orenstein & Koppel Mallet Magnet Tramway Tasmania 0-4-4-0T 8,878 lb. 4.5 tons
Heeresfeldbahn Brigadelok 0-8-0T 6,528 lb. 3 tons
Single Fairlie (Taliesin) 0-4-4T 5,422 lb. ? tons
Pechot-Bourdon 0-4-4-0T 5,065 lb. 3.5 tons

1. All these TEs are subject to review taking into account complex matters such as gearing, compounding and the accuracy and currency of quoted statistics

2. As quoted by manufacturer

3. The K1 TE Calculation is complicated by it being a compound locomotive. This TE is that calculated for it in compound mode with the transfer pipe at 52 psi. A higher starting TE of around 17,000 lb. can be achieved by use of a simpling valve that allows the HP cylinders to vent directly to the blast pipe and the LP receiver to be charged to 80 psi from the boiler. The plumbing involved means that this is only useful to get a train moving from rest as the receiver will rapidly be discharged and no useful effort will be provided by the LP cylinders.

See also[edit]

References[edit]

External Links[edit]

  • listing - Shows all the steam locomotives used on the South African and South-West African government 2ft gauge lines.
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