South African Dutton road-rail tractors
Dutton rail-only tractor no. RR1155, c. 1924
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| Type and origin | |
|---|---|
| Power type | Internal combustion (prototype) Steam (production models) |
| Designer |
South African Railways (Maj Frank Dutton) |
| Builder |
Dennis (prototype) Yorkshire (production models) |
| Build date | 1917-1924 |
| Total produced | 3 |
| Rebuilder | Britannia Engineering Works |
| Rebuild date | 1923-1924 |
| Specifications | |
|---|---|
| Configuration: |
|
| • Whyte |
4-2-0 (Jervis) - R1501 & RR973 4-2-4 (Huntington) - RR1155 |
| • UIC | 2An2t - R1501 & RR973 2A2n2t - RR1155 |
| Gauge | 2 ft (610 mm) narrow |
| Axle load | 3,000 lb (1,361 kg) (prototype) |
| • Leading | 3,000 lb (1,361 kg) (prototype) |
| • Coupled | 5,655 lb (2,565 kg) (off-rail) |
| Adhesive weight | 5,655 lb (2,565 kg) (prototype) |
| Fuel type | Power paraffin (prototype) Coal (production models) |
| Cylinders | Four (prototype) Two (production models) |
| Couplers | Drawbar and pin |
| Performance figures | |
|---|---|
| Power output | 35 hp (26 kW) (prototype) |
| Career | |
|---|---|
| Operators | South African Railways |
| Number in class | 3 |
| Numbers | R1501, RR973, RR1155 |
| First run | 1923-1924 |
| Last run | 1927 |
The South African Railways Dutton road-rail tractors of 1923 were road-rail steam tractors.
In 1917, the South African Railways conducted trials with a prototype petrol-paraffin powered Dutton road-rail tractor. In 1924, it placed two production model steam rail tractors in service on the new narrow gauge line between Naboomspruit and Singlewood in Transvaal. One was constructed as a 4-2-0 road-rail tractor while the other was constructed as a bi-directional 4-2-4 rail-only tractor.
The non-profitability of many branch line operations had been a problem for the South African Railways (SAR) from the outset. The question of non-paying branch lines was raised by Sir William Hoy, South African Railways and Harbours General Manager, in a paper read before the Imperial Motor Transport Conference in London in 1913. He drew attention to the fact that, in isolated districts with vast agricultural and mineral capabilities in many parts of the Union of South Africa, development was hampered by the lack of means of transportation.
In an attempt to assist in solving the branch line problem, Major Frank Dutton, SAR Signal Engineer and the Motor Transport Superintendent, developed and took out several patents on a loco-tractor system. The aim was to replace or eliminate the steam locomotive on non-profitable branch lines since he considered the locomotive to be the main deciding factor on the questions of grades, curves and weight of rails, which governed the cost of construction.
Dutton argued that a rubber tyre in contact with a hard road would be better at transferring tractive power than a steel wheel on steel rail. He claimed that the tractive effort to be obtained by using rubber-tyred driving wheels running on roads was 1,330 pounds (603 kilograms) per long ton of adhesive weight, compared to the 334 pounds (151 kilograms) per long ton which could be obtained by using steel wheels running on rails. His proposed system would use railway trucks on rails, hauled by a rail-and-road-borne tractor which would be guided by a four-wheeled bogie on the rails, but with driving wheels fitted with solid rubber tyres which would run on well-prepared strips of road on each side of the rail track.
In 1917, General Manager Hoy authorised a trial of the system and a test circuit was laid on the veld at Canada Junction, 9 miles (14 kilometres) from Johannesburg. The dog-bone test circuit was 742 yards (678 metres) around, laid with light 16 pounds per yard (8 kilograms per metre) rails on 7 pounds (3 kilograms) steel sleepers and hook bolts. The track included tight curves of as low as 37 feet (11 metres) radius and steep gradients of as much as 1 in 17 (5.88%).
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