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

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

NG G11 no. 54 Solly at Chelsea on 3 April 1990

Type and origin ♠ Saturated steam locomotives ♥ Superheated steam locomotives Power type Steam Designer Beyer, Peacock and Company Builder Beyer, Peacock and Company Serial number 5975-5977, 6199-6200 Model Class NG G11 Build date 1919-1925 Total produced 5

Specifications Configuration 2-6-0+0-6-2 (Double Mogul) Driver 3rd & 4th coupled axles Gauge 2 ft (610 mm) narrow Leading dia. 21 in (533 mm) Coupled dia. 30 in (762 mm) Wheelbase ♠ 39 ft (11,887 mm) ♥ 39 ft 9 in (12,116 mm)  • Engine 10 ft 3 in (3,124 mm) each  • Coupled 5 ft 9 in (1,753 mm) each Pivot centres ♠ 22 ft (6,706 mm) ♥ 22 ft 9 in (6,934 mm) Length: ​  • Over couplers ♠ 44 ft 7 1⁄2 in (13,602 mm) ♥ 45 ft 5 in (13,843 mm) Height 10 ft 4 in (3,150 mm) Frame type Plate Axle load ♠ 6 LT 3 cwt 3 qtr (6,287 kg) ♥ 6 LT 11 cwt (6,655 kg)  • Leading ♠ 4 LT 7 cwt 1 qtr (4,433 kg) front 4 LT 5 cwt (4,318 kg) rear ♥ 4 LT 16 cwt (4,877 kg) front 4 LT 15 cwt 3 qtr (4,864 kg) rear  • 1st coupled ♠ 6 LT (6,096 kg) ♥ 6 LT 9 cwt 2 qtr (6,579 kg)  • 2nd coupled ♠ 6 LT 1 cwt 2 qtr (6,172 kg) ♥ 6 LT 8 cwt 2 qtr (6,528 kg)  • 3rd coupled ♠ 5 LT 17 cwt (5,944 kg) ♥ 6 LT 4 cwt 3 qtr (6,338 kg)  • 4th coupled ♠ 6 LT 0 cwt 2 qtr (6,122 kg) ♥ 6 LT 8 cwt 2 qtr (6,528 kg)  • 5th coupled ♠ 6 LT 3 cwt 3 qtr (6,287 kg) ♥ 6 LT 11 cwt (6,655 kg)  • 6th coupled ♠ 6 LT (6,096 kg) ♥ 6 LT 10 cwt 3 qtr (6,642 kg) Adhesive weight ♠ 36 LT 2 cwt 3 qtr (36,720 kg) ♥ 39 LT 3 cwt (39,780 kg) Loco weight ♠ 44 LT 15 cwt (45,470 kg) ♥ 48 LT 4 cwt 3 qtr (49,010 kg) Fuel type Coal Fuel capacity 2 LT 10 cwt (2.5 t) Water cap 970 imp gal (4,410 l) front 380 imp gal (1,730 l) rear Firebox type Belpaire  • Firegrate area ♠ 19.3 sq ft (1.79 m2) ♥ 19.5 sq ft (1.81 m2) Boiler: ​  • Pitch 5 ft 3 in (1,600 mm)  • Diameter 4 ft 2 in (1,270 mm)  • Tube plates 9 ft 3 3⁄8 in (2,829 mm)  • Small tubes ♠ 211: 1 3⁄4 in (44 mm) ♥ 115: 1 3⁄4 in (44 mm)  • Large tubes ♥ 13: 5 1⁄2 in (140 mm) Boiler pressure 180 psi (1,241 kPa) Safety valve Ramsbottom Heating surface ♠ 980 sq ft (91 m2) ♥ 741.5 sq ft (68.89 m2)  • Tubes ♠ 899 sq ft (83.5 m2) ♥ 660.9 sq ft (61.40 m2)  • Firebox ♠ 81 sq ft (7.5 m2) ♥ 80.6 sq ft (7.49 m2) Superheater: ​  • Heating area ♥ 141.5 sq ft (13.15 m2) Cylinders Four Cylinder size 10 1⁄2 in (267 mm) bore 16 in (406 mm) stroke Valve gear Walschaerts Valve type ♠ Slide - ♥ Piston Couplers Bell-and-hook (Cape) Johnston link-and-pin (Natal)

Performance figures Tractive effort ♠♥ 15,876 lbf (70.62 kN) @ 75%

Career Operators South African Railways Class Class NG G11 Number in class 5 Numbers ♠ NG51-NG53 - ♥ NG54-NG55 Delivered 1919-1925 First run 1919 Withdrawn 1962-1974 Preserved 3

The South African Railways Class NG G11 2-6-0+0-6-2 of 1919 was a narrow gauge steam locomotive.

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.

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.

On the 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. It was to become the first Garratt to enter SAR service.

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

The same problem also existed on Cape gauge light-rail single-line 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-aligning large parts of the lines to accommodate heavier locomotives. Either method was expensive and, in such conditions, the Garratt design had distinct advantages.

On a Garratt locomotive, the shared boiler and cab are carried on a cradle frame which is suspended on pivot centres attached to the frames of the two engine units, which are both free to align itself to the track curvature. To accommodate the pivoting, the steam and exhaust pipes have flexible connections between the engine units and the central cradle.

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. The use of a Garratt locomotive enables the capacity of a line to be approximately doubled without having to strengthen the track, bridges and culverts, or re-align the curvature.