South African Dutton road-rail tractors

South African Dutton road-rail tractors

300px Dutton rail-only tractor no. RR1155, c. 1924

Type and origin Power type Internal combustion (Prototype) Steam (Production) Designer South African Railways (Frank Dutton) Builder Dennis (prototype), Yorkshire Patent Steam Wagon Co. Build date 1917-1924 Total produced 3 Rebuilder Britannia Engineering Works

Specifications Gauge 2 ft (610 mm) narrow Axle load:  • Leading (Prototype) Adhesive weight (Prototype) Fuel type Power paraffin (Prototype) Coal (Production) Cylinders Four (Prototype) Couplers Drawbar and pin

Performance figures Power output 35 hp (26 kW) (Prototype)

Career Operators South African Railways Number in class 3 Numbers R1501, RR1155, RR973 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 road-rail tractor and, in 1924, placed at least two steam road-rail tractors in service on the new narrow gauge line between Naboomspruit and Singlewood in Transvaal.

Branchline non-profitability

The non-profitability of many branchline operations had been a problem for the South African Railways (SAR) from the outset. The question of non-paying branchlines 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.

Development

In an attempt to assist in solving the branchline 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 branchlines, 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.

File:Canada Junction test track.jpg

Canada Junction test track layout

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%).

The prototype loco-tractor was a modified Dennis tractor, powered by a 35 horsepower (26 kilowatts) four-cylinder petrol-paraffin engine, which was fitted with a removable bogie between the front wheels to lift them high enough to prevent ground contact. A ball pin on the bogie fitted into a socket under the front axle, and the bogie could easily be removed or replaced by running the tractor up a pair of ramps, placed on both sides of the track. The tractor's weight distribution was on the rail and on the rubber-tyred driving wheels.. A drawing of the tractor in the patent document shows a number of refinements considered at the time but not actually fitted to the Dennis tractor, namely a six-cylinder engine, steerable rear wheels for use when reversing on the rail, and a power-operated screw-jacking system to raise the front road wheels so as to obviate use of the ramps.

Singlewood Branch

The experiments proved successful and authority was granted in 1923 to construct a 2 ft (610 mm) narrow gauge line from Naboomspruit to Singlewood, built to the Stronach-Dutton system, the low cost of construction being one of the motivating factors. The section to Crecy was completed on 15 April 1924 and the full 20 miles 47 chains (33.1 kilometres) line to Singlewood was opened on 22 September of that same year.

At least two tractors were used on this road-rail line, both steam-powered and both rebuilt by the Britannia Engineering Works of Johannesburg from Yorkshire Patent Steam Wagon Co. steam tractors.

• One, no. RR973, was a modified Yorkshire steam tractor, fitted with jacks at the front, to allow a separate bogie to be manoeuvred into position underneath the front axle to guide it on the rails. Without the bogie, the vehicle could still be driven on ordinary roads and had the advantage of being able to be detached and run around the train, without requiring special loops for that purpose.
• The other, no. RR1155, underwent more drastic modification to turn it into a rail-only vehicle. It had a bogie at either end with the single pair of driving wheels on a differential axle in the centre, and was arranged for forward and reverse movement at all speeds. While it was reversible, it could only be used on the rails. Since, on occasion, the vehicle had to be transported by road, its construction was such that it could be readily disassembled into more easily transportable units, to be moved on road wheels to a workshop or for transfer of any other kind.

British Empire Exhibition

The Stronach-Dutton system was promoted by a company called Roadrails Ltd. who exhibited and demonstrated it at the 1924-25 British Empire Exhibition at Wembley, where it was presented as a solution to the transport problems which were experienced in several British Colonies. Similar systems were introduced or at least demonstrated in many countries, colonies and territories, which included Australia, England, India, Morocco, Palestine, Scotland, Spain, Uganda and Tasmania, though almost all of the known installations were initiated before the Wembley exhibition. Several different tractors were used at Wembley, mostly supplied by William Beardmore and Company but not the Yorkshire type as used in South Africa. Although it was popular as a ride, as a sales promotion it seems to have been a failure and did not reopen to the public for the 1925 season of the Exhibition.

Termination

In South Africa also the system was short-lived. The tractive effort per ton of axle load which was assumed by Dutton for the loco-tractor was found to be unduly optimistic, while that for rail traction was unduly pessimistic. The system of combined road-and-rail turned out to have the limitations of both and advantages of neither.

However the line seemed to be successful and as traffic grew more motive power was needed and the Yorkshires were joined by Class NG6 Lawley no. NG98. By 1927, it was joined by Lawley no. NG103, but by this time the loco-tractor system was already terminated. By 17 October 1927, the Singlewood branch was regauged to 3 ft 6 in (1,067 mm) Cape gauge for regular steam locomotive working and, by 11 June 1928, it was extended to Zebediela.

Illustration

• Dutton Road-Rail Tractor prototype no. RR1501 a.jpg

  Power-paraffin fueled Dennis tractor, prior to modification to Dutton road-rail tractor no. R No 1501

• Dutton Road-Rail Tractor prototype no. RR1501 d.jpg

  Prototype no. R No 1501 being demonstrated to Sir William Hoy, seated next to the driver, Canada Junction, August 1920

• Dutton Road-Rail Tractor prototype no. RR1501 f.jpg

  Prototype no. R No 1501 demonstrating shedding its bogie, Canada Junction, August 1920

• Dutton's Road-Rail Tractor no. RR973.jpg

  Road-Rail tractor no. RR973, a modified Yorkshire steam tractor, c. 1924

• Dutton Road-Rail Tractor no. RR1155 c.jpg

  Dutton reversible rail-only tractor no. RR1155, rebuilt from a Yorkshire steam tractor, in service on the Singlewood branch, c. 1925