South African Class GM 4-8-2+2-8-4

South African Class GM 4-8-2+2-8-4

No. 2298 at Krugersdorp, 23 April 1970

Type and origin Power type Steam Designer South African Railways (W.A.J. Day) Builder Beyer, Peacock and Company Serial number 6883-6898 Model Class GM Build date 1938 Total produced 16

Specifications Configuration 4-8-2+2-8-4 (Double Mountain) Driver 3rd & 6th coupled axles Gauge 3 ft 6 in (1,067 mm) Cape gauge Leading dia. 28 1⁄2 in (724 mm) Coupled dia. 54 in (1,372 mm) Trailing dia. 34 in (864 mm) Tender wheels 34 in (864 mm) Wheelbase 86 ft 4 in (26,314 mm)  • Engine 29 ft 10 in (9,093 mm) each  • Leading 6 ft 4 in (1,930 mm) each  • Coupled 14 ft 5 in (4,394 mm) each  • Tender 35 ft 9 in (10,897 mm)  • Tender bogie 5 ft 9 in (1,753 mm) Pivot centres 43 ft (13,106 mm) Wheel spacing (Asymmetrical) 1-2: 4 ft 10 in (1,473 mm) each 2-3: 4 ft 9 in (1,448 mm) each 3-4: 4 ft 10 in (1,473 mm) each Length: ​  • Over couplers 93 ft 4 1⁄2 in (28,461 mm) engine 43 ft 10 4⁄5 in (13,381 mm) tender 137 ft 3 3⁄10 in (41,841 mm) total Width 10 ft (3,048 mm) Height 13 ft (3,962 mm) Frame type Bar Axle load 15 LT (15,240 kg)  • Leading 17 LT 16 cwt (18,090 kg) front 18 LT 5 cwt (18,540 kg) rear  • 1st coupled 13 LT 15 cwt (13,970 kg)  • 2nd coupled 14 LT 11 cwt (14,780 kg)  • 3rd coupled 14 LT 19 cwt (15,190 kg)  • 4th coupled 14 LT 3 cwt (14,380 kg)  • 5th coupled 14 LT (14,220 kg)  • 6th coupled 15 LT (15,240 kg)  • 7th coupled 14 LT 15 cwt (14,990 kg)  • 8th coupled 13 LT 19 cwt (14,170 kg)  • Trailing 11 LT 13 cwt (11,840 kg) front 11 LT 10 cwt (11,680 kg) rear  • Tender bogie 24 LT 17 cwt 3 qtr (25,290 kg)  • Tender axle 12 LT 8 cwt 3 qtr (12,640 kg) Adhesive weight 115 LT 2 cwt (116,900 kg) Loco weight 174 LT 6 cwt (177,100 kg) Tender weight 49 LT 15 cwt 3 qtr (50,590 kg) Total weight 224 LT 1 cwt 3 qtr (227,700 kg) Tender type X-17 (2-axle bogies) X-17, X-20 permitted Fuel type Coal Fuel capacity 10 LT (10.2 t) Water cap 1,600 imp gal (7,270 l) engine Tender cap 6,750 imp gal (30,700 l) Firebox type Round-top  • Firegrate area 64 sq ft (5.9 m2) Boiler: ​  • Pitch 8 ft 6 in (2,591 mm)  • Diameter 7 ft (2,134 mm)  • Tube plates 13 ft 6 1⁄2 in (4,128 mm)  • Small tubes 255: 2 in (51 mm)  • Large tubes 50: 5 1⁄2 in (140 mm) Boiler pressure 200 psi (1,379 kPa) Safety valve Ross-pop Heating surface 3,066 sq ft (284.8 m2)  • Tubes 2,785 sq ft (258.7 m2)  • Firebox 281 sq ft (26.1 m2) Superheater: ​  • Heating area 778 sq ft (72.3 m2) Cylinders Four Cylinder size 20 1⁄2 in (521 mm) bore 26 in (660 mm) stroke Valve gear Walschaerts Valve type Piston Valve travel 6 1⁄2 in (165 mm) Couplers AAR knuckle

Performance figures Tractive effort 60,700 lbf (270 kN) @ 75%

Career Operators South African Railways Class Class GM Number in class 16 Numbers 2291-2306 Delivered 1938-1939 First run 1938 Withdrawn 1974

The South African Railways Class GM 4-8-2+2-8-4 of 1938 was an articulated steam locomotive.

During 1938 and 1939, the South African Railways placed sixteen Class GM Garratt articulated steam locomotives with a 4-8-2+2-8-4 Double Mountain type wheel arrangement in goods train service on the Mafeking line out of Johannesburg.

By 1938, the rapidly increasing traffic on the line from Johannesburg via Krugersdorp and Zeerust to Mafeking necessitated some means to increase its capacity quickly. Electrification to at least as far as Koster was proposed, but would take a considerable time to complete. This led W.A.J. Day, Chief Mechanical Engineer (CME) of the South African Railways (SAR) from 1936 to 1939, to prepare designs for a Garratt locomotive which would be equal to two Class 19D locomotives.

The initial designs of the Class GM Garratt were rejected by the Chief Civil Engineer, however, since the weight on the leading and trailing bogies of each engine unit would exceed the acceptable limit for the 60 pounds per yard (30 kilograms per metre) rail of the Mafeking line. To overcome the axle load objections, the water capacity of the front water tank was reduced to 1,600 imperial gallons (7,270 litres) while the rear bunker was redesigned to carry no water and with a coal capacity of 10 long tons (10.2 tonnes). The meagre water supply, which would really only be sufficient for shunting purposes, would be augmented by semi-permanently coupling a purpose-built auxiliary water tender to the locomotive.

In effect, since Garratt locomotives had hitherto been considered as tank engines because they carry all their water on board, this arrangement introduced the tank-and-tender Garratt. In all other respects, Day's design followed that of the heavy Class GL Garratt. An order for sixteen locomotives was placed with Beyer, Peacock and Company in 1938, while the sixteen Type X-17 water tenders were built in the Pietermaritzburg shops. The locomotives were delivered in 1938 and 1939, erected in the Durban shops and numbered in the range from 2291 to 2306.