South African Class 61-000

South African Railways Class 61-000

Company type	Diesel-hydraulic locomotive
Industry	Rail transport
Predecessor	Class 1-DH
Founded	1959 (1959)
Headquarters	South Africa
Products	Locomotives (Henschel DH-1420 model)
Parent	South African Railways

South African Railways Class 61-000 Diesel-Hydraulic Locomotive

The Class 61-000 diesel-hydraulic locomotive was introduced by the South African Railways in 1959.

During the period from May to July 1959, South African Railways commissioned seven Henschel DH-1420 model locomotives, initially designated as Class 1-DH. This acquisition aimed to broaden operational knowledge by incorporating diesel-hydraulic technology alongside the existing diesel-electric traction methods. Subsequently, these locomotives were redesignated as Class 61-000. In 1971, six units were transferred to Rhodesia Railways, which later became part of the National Railways of Zimbabwe.

Manufacturer

The Class 61-000 DH-1420 diesel-hydraulic locomotives were developed and constructed for the South African Railways (SAR) by Henschel & Son located in Kassel, Germany. When initially delivered, these units were classified as Class 1-DH and assigned numbers from D745 to D751 within the non-steam locomotive numbering series, a range predominantly reserved for electric locomotives until then. Notable exceptions included the Class DS, Class DS1, and Class 1-DE diesel-electric classes. Following the SAR’s adoption of a revised diesel locomotive classification and numbering system later in 1959, coinciding with the introduction of the Class 32-000, these locomotives were reclassified as Class 61-000 and renumbered from 61-001 through 61-007.

The acquisition of the Class 1-DH units occurred one year after SAR had introduced its first large-scale diesel-electric fleet, the Class 1-DE, which entered service in 1958 and was subsequently reclassified as Class 31-000. At that time, steam traction was still heavily utilized alongside growing adoption of electric traction. The initial mainline diesel traction investments therefore included both diesel-electric (Class 1-DE) and diesel-hydraulic (Class 1-DH) types to evaluate the advantages of each diesel propulsion method.

Diesel-hydraulic transmission

Diesel-electric locomotives typically employ a diesel engine prime mover that drives either a DC generator or an AC alternator to produce electrical energy. This electricity powers axle-mounted electric traction motors, one per driven axle, which in turn propel the wheels. This system operates on principles similar to those of conventional electric locomotives, differing mainly in that they generate their own electrical power rather than sourcing it externally from overhead lines or third rails.

Conversely, diesel-hydraulic locomotives utilize hydrokinetic, or hydrodynamic, transmission systems. These employ torque converters to transfer power mechanically from the prime mover directly to the wheels.

Characteristics

The Class 61-000 featured a centre-cab design powered by two General Motors Electro-Motive Division (GM-EMD) type 6/567C V6 engines. Each engine was coupled with a Voith L306r triple-torque converter transmission unit, delivering power to one bogie’s wheels via drive shafts. Unlike diesel-electrics where each axle is independently powered by its own traction motor allowing for individual wheel-slip control, the axles on each bogie of the Class 61-000 were mechanically linked through drive shafts, preventing independent wheel-slip.

The cab was equipped with dual control stands. Since it was possible to control all six prime movers across three multiple-unit coupled locomotives from a single cab, each stand included six engine start buttons and six engine stop buttons. The electrical system was notably complex and suffered reliability issues, leading to a comprehensive rewiring effort in 1963.

These diesel-hydraulic units were procured to directly compare performance against the General Electric-built Class 31-000 diesel-electrics. Despite having a higher nominal starting tractive effort of approximately 197.2 kilonewtons (44,300 pounds-force) compared to the 181 kilonewtons (41,000 pounds-force) offered by the diesel-electrics, they encountered persistent problems such as overheating. This underperformance was disappointing given the proven success of diesel-hydraulic technology in Germany. While it has been speculated that South Africa’s significantly warmer climate may have contributed to these issues, it is likely that enhanced cooling systems could have mitigated such problems if they had been the primary cause.

South African Railways

Following its inception in late 1958, the Germiston diesel depot became the primary source of power for freight trains, as well as certain passenger services traveling southward from the Reef towards Volksrust and Kroonstad. Upon arrival, the Class 61-000 locomotives joined the existing Class 31-000 units at this location. Initially, these locomotives were tested on passenger routes; however, after experiencing overheating issues near Standerton while operating the Trans-Natal Express, they were withdrawn from passenger duties and reassigned exclusively to freight services. Their performance on mainline freight operations was also unsatisfactory, leading to their predominant use in shunting tasks within yards around Braamfontein by the early 1960s.

Throughout their tenure with South African Railways, the Class 61-000 fleet remained based at the Germiston diesel depot. Notably, locomotive number 61-006 was involved in a head-on collision at Kaserne on 8 October 1966 and was subsequently dismantled at the Koedoespoort workshops in Pretoria by September 1968. The discovery of cracked axles led to the entire fleet being withdrawn for repairs during 1967.

Rhodesia Railways

In 1971, six remaining locomotives were transferred to Rhodesia Railways (RR), which later became the National Railways of Zimbabwe (NRZ). Upon acquisition, they were reclassified as RR Class DH1 and renumbered sequentially from 3101 through 3106.

ZISCO

Subsequently, these units were sold to the Zimbabwe Iron and Steel Company (ZISCO) located in KweKwe, Zimbabwe. The majority, if not all, had been scrapped by the year 2001.

Liveries

The locomotives originally sported a paint scheme identical to that of the South African Class 31-000 diesel-electrics, featuring a design inspired by the South African flag: white on the upper body and blue below, separated by an orange stripe along the sides and complemented by orange whiskers at each end. Additional details included black running boards, red buffer beams, and black cowcatchers. Starting in 1960, this color scheme was gradually phased out in favor of Gulf Red with yellow side stripes on the hoods and a distinctive yellow "V" shape painted on both ends.

Works Numbers

The table below details the builder's works numbers assigned to the Class 61-000 locomotives, along with their renumbering following reclassification and subsequent sales.

Works Numbers and Renumbering of Class 61-000

Original SAR 1-DH Number	SAR Class 61-000 Number	Henschel Works Number	RR & NRZ Number
D745	61-001	29745	3101
D746	61-002	29746	3102
D747	61-003	29747	3103
D748	61-004	29748	3104
D749	61-005	29749	3105
D750	61-006	29750
D751	61-007	29751	3106

Illustration

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  Locomotive No. D750, subsequently renumbered 61-006, pictured during assembly at Henschel's Kassel facility in Germany, 1958

External links

Media related to South African Class 61-000 at Wikimedia Commons