South African Class 61 000

Manufacturer

The Class 61-000 type DH-1420 diesel-hydraulic locomotive was designed and built for the South African Railways (SAR) by Henschel and Son in Kassel, Germany. Upon delivery, the locomotives were classified as Class 1-DH and numbered in the range from D745 to D751. When the SAR adopted a new classification and numbering system for electric- and diesel-powered locomotives c. 1960, they were reclassified as Class 61-000 and renumbered in the range from 61-001 to 61-007.

The Class 1-DH was acquired a year after the SAR had acquired its first diesel-electric locomotives to be built in quantity, the Class 1-DE, which had entered service in 1958 and which was later reclassified to Class 31-000. At the time, the SAR was still making extensive use of steam traction and limited use of electric traction. Its first diesel traction acquisitions were therefore the diesel-electric Class 1-DE and diesel-hydraulic Class 1-DH, to gain experience with both forms of diesel motive power.

Diesel-hydraulic transmission

The more commonly used diesel-electric locomotive makes use of a diesel engine prime mover to propel either a generator (DC) or an alternator (AC) to generate electric power, which is then used to propel axle-hung electric traction motors, one per powered axle, to drive the locomotive wheels. It therefore works on the same principle as a regular electric locomotive, the only difference being that it generates its own electric power instead of collecting it from an external supply such as overhead catenary or a third rail.

Diesel-hydraulic locomotives, on the other hand, use hydrokinetic transmission, also known as hydrodynamic transmission, in the form of torque converters to transmit power from prime mover to wheels.

Characteristics

The Class 61-000 was a centre-cab locomotive which was powered by two General Motors Electro-Motive Division (GM-EMD) type 6/567C V6 prime movers, each with a Voith type L306r triple-converter torque converter and each driving the wheels of one bogie. Power was transferred to the axles through drive shafts. Unlike diesel-electric locomotives, where each axle is driven by its own traction motor, individual wheel-slip was not possible on the Class 61-000, since each bogie's two axles were interconnected through the drive shafts.

The cab had two control stands and, since it was possible to start the six prime movers in three consisted locomotives from one engine cab, each control stand had six engine start buttons and six engine stop buttons. The electrical system was very complicated and unreliable, which eventually led to the locomotives being completely rewired in 1963.

South African Railways

The Class 61-000s spent their entire SAR working lives stationed at the Germiston diesel depot. One of them, no. 61-006, was involved in a head-on collision at Kaserne on 8 October 1966, and was eventually scrapped at the Koedoespoort workshops in Pretoria in September 1968. Problems with cracked axles resulted in the rest of the fleet being staged for repairs in 1967.

Rhodesia Railways

In 1971, the remaining six locomotives were sold to Rhodesia Railways (RR), later renamed the National Railways of Zimbabwe (NRZ), where they became the RR Class DH1 and were renumbered in the range from 3101 to 3106.

ZISCO

They were eventually resold to the Zimbabwe Iron and Steel Company (ZISCO) steel works at KweKwe in Zimbabwe. Most, if not all, were scrapped by 2001.

Works numbers

The Class 61-000 builder's works numbers and renumbering upon reclassification and sale, are listed in the table.