Sulzer Marine Diesel Engines: History 1898 to 1997

Background

Sulzer Brothers is the historical name for Gebrüder Sulzer, an industrial firm founded in 1834 in Winterthur, Switzerland. Originally a foundry, Sulzer industrialised pump, textile machinery, and heating equipment production through the 19th century. In the early 20th century, the company entered marine diesel engine manufacturing, becoming one of the dominant slow-speed two-stroke designers worldwide for nearly a century.

Sulzer’s engineering legacy in marine propulsion is direct and pervasive. The company:

• Developed one of the first practical marine diesel engines in 1898
• Installed engines on one of the first sea-going two-stroke motor ships (the Monte Penedo, 1912)
• Introduced the RD (1957), RND (1968), RTA (1983), and RT-flex (2001) slow-speed two-stroke series, each defining the state of the art in its era
• Pioneered common-rail electronic injection on slow-speed engines (RT-flex, 2001)
• Was the principal European competitor to Burmeister & Wain (later MAN B&W) for nearly a century

In 1997, Sulzer divested its marine diesel business to Wartsila, ending its independent operation in the segment after 99 years. The Sulzer engine lineage continued under Wartsila branding through the 2000s and was reorganised in 2015 as the joint venture Winterthur Gas & Diesel (WinGD), jointly owned with CSSC. CSSC became sole owner in 2016. WinGD remains headquartered in Winterthur and is the direct corporate and technical descendant of pre-1997 Sulzer.

This article covers Sulzer’s marine diesel engineering history in detail, with particular emphasis on the engine series that defined each era.

Founding and early diesel work (1834-1910)

Foundry origins

Johann Jakob Sulzer-Neuffert founded the foundry in Winterthur in 1834. His sons Johann Jakob Sulzer-Hirzel and Salomon Sulzer-Sulzer industrialised the business through the mid-19th century, expanding into pumps, steam engines, textile machinery, and central heating equipment. By the 1880s Sulzer was a major Swiss industrial firm with international export operations.

First diesel agreement

In 1893, Sulzer Brothers signed an agreement with Rudolf Diesel for collaboration on the new engine concept. The agreement gave Sulzer rights to manufacture diesel engines under licence. Diesel himself spent time at the Winterthur works during the development period.

First Sulzer diesel engine

The first Sulzer diesel engine was completed and started running on 10 June 1898. It was a single-cylinder four-stroke engine: 260 mm bore, with output approximately 14.7 kW (20 hp) at 160 rpm. The engine was a pure laboratory development unit; the design was used to verify Diesel’s concept and explore the practical engineering challenges.

Series production

In 1903 Sulzer began series manufacture of diesel engines in Winterthur, supplying primarily stationary and industrial applications. Marine adaptation began in parallel, with the technical challenges of reversibility and reliability in marine service requiring substantial engineering work.

First reversing two-stroke marine engine

In 1905 Sulzer built its first reversing two-stroke marine diesel engine. Reversibility was a fundamental marine requirement — slow-speed engines had to operate in either rotation direction for ship manoeuvring — and Sulzer’s solution involved a mechanical camshaft shift mechanism. The 1905 engine demonstrated the principle but was not put into commercial service.

Demonstration and trials

Through the 1900s and 1910s, Sulzer and competitors (notably MAN, B&W, and Werkspoor) raced to put the first diesel engine into commercial sea-going service. Sulzer engines were trialled on inland Swiss vessels and other test platforms. The 1910 demonstration on a Lake Geneva tug-icebreaker showed diesel propulsion was competitive with steam.

First sea-going installations (1910-1930)

Werkspoor’s Vulcanus (1910)

The first sea-going diesel-powered ship, with Werkspoor (Netherlands) engines, entered service in 1910: the tanker MV Vulcanus. This was a four-stroke installation. Sulzer engines reached sea-going service shortly afterwards.

Sulzer’s Monte Penedo (1912)

In 1912, the German cargo vessel MV Monte Penedo entered service equipped with two Sulzer 4S47 valveless crosshead two-stroke engines, with combined output approximately 1,250 kW. Monte Penedo was one of the first ocean-going two-stroke motor ships and is a milestone in marine diesel history.

The competing milestone in the same year was Burmeister & Wain’s MS Selandia, a four-stroke twin-engine installation. Selandia is generally considered the first ocean-going passenger/cargo motor ship, with Sulzer’s Monte Penedo following closely as the first ocean-going two-stroke motor ship.

Early product lineage

Sulzer’s pre-1920 marine engines were small to mid-power four-stroke and two-stroke units, mostly trunk-piston for smaller applications. The valveless two-stroke crosshead design (used on Monte Penedo) was a Sulzer engineering distinctive: scavenge and exhaust ports cut into the cylinder liner, no cylinder cover valves, and reversibility through a camshaft shift mechanism.

Continued development through the 1920s

Through the 1920s, Sulzer expanded its range of marine engines and grew its export business. Engines were built at Winterthur and licensed to manufacturers in other countries. Notable licensees included:

• Götaverken (Sweden, from 1915 — though Götaverken later switched to its own design)
• Mitsui Engineering & Shipbuilding (Japan, technical agreement from 1948 onwards)
• Hawthorn-Leslie / Hawthorn-Doxford (UK, in some periods)

Inter-war and wartime (1923-1945)

Double-acting two-stroke experiments

In 1923, Sulzer introduced double-acting two-stroke designs, where the piston worked on both up and down strokes. These engines had higher power per cylinder but were mechanically complex (two-sided fuel injection, dual sealing surfaces) and were eventually abandoned. The double-acting line ran into the 1930s before being discontinued.

Loop scavenging dominance

By the 1930s Sulzer had standardised on loop scavenging for two-stroke marine engines: scavenge and exhaust ports both cut into the cylinder liner, both opened and closed by piston motion, with the airflow forming an inverted-U pattern through the cylinder. Loop scavenging avoided the mechanical complexity of cylinder cover valves and was Sulzer’s signature configuration through the next four decades. This contrasts with Burmeister & Wain, which adopted uniflow scavenging (with cover valves) earlier.

Wartime production

Through World War II Sulzer continued marine diesel production for Swiss-flagged and friendly-nation merchant vessels. Switzerland’s neutrality limited military diesel work, but Sulzer engines powered numerous neutral-flag merchant ships through the conflict.

Post-war expansion (1946-1968)

Turbocharging

In 1946 Sulzer introduced turbocharging for normal continuous service on the 6TAD48 engine. Turbocharging substantially raised specific output and was rapidly adopted across the marine diesel industry.

RD series (1957)

In 1957 Sulzer launched the RD series, a comprehensive new design that became the company’s mainstream marine two-stroke product into the late 1960s. RD engines:

• Used pulse turbocharging (later replaced by constant-pressure)
• Had rotary exhaust valves — a Sulzer-specific configuration
• Were available in bores from 440 mm (5RD44) to 900 mm (12RND90)
• Spanned a wide power range, from a few thousand kW to over 30,000 kW

The RD series was Sulzer’s principal commercial product for over a decade and powered many of the world’s tankers, container ships, and bulk carriers.

“R” naming

The “R” prefix derives from Sulzer’s earlier 1950s RSD type, where R stood for revidiert (German: “revised”) — an early Sulzer in-house designation that became standardised through the engine lineage. The R prefix continues today in WinGD’s product names, though the official lineage tracing has been more loosely maintained.

RND series (1968)

In 1968 Sulzer introduced the RND series. Compared to RD, the RND:

• Replaced rotary exhaust valves with port-only scavenging (loop scavenging without separate exhaust valves)
• Simplified the cylinder cover assembly
• Improved reliability and reduced maintenance burden
• Achieved similar power outputs at slightly improved fuel efficiency

The RND was an evolutionary step within Sulzer’s loop-scavenging architecture. It served Sulzer through the 1970s and into the early 1980s.

Sulzer’s first gas-fuelled engine (1972)

In 1972 Sulzer fitted its first gas-fuelled marine diesel on an LNG carrier — an early experiment in dual-fuel operation that anticipated the modern X-DF and ME-GI families. The 1972 installation was an isolated milestone; commercial dual-fuel operation at scale waited for the 2010s.

RTA series — the uniflow pivot (1983)

Strategic context

By the late 1970s the marine diesel industry was reaching the limits of loop scavenging. Container ship and supertanker propulsion increasingly demanded very long stroke engines (stroke-to-bore ratios above 3.0) to drive larger, slower, more efficient propellers. Loop scavenging required scavenge and exhaust ports near the bottom of the cylinder — but with very long stroke, the available crank-angle window for gas exchange became insufficient.

Burmeister & Wain had already standardised on uniflow scavenging (single hydraulically actuated central exhaust valve in the cylinder cover) and was demonstrating the architecture’s superior gas-exchange characteristics for very long stroke engines. Sulzer faced a strategic decision: continue loop scavenging at increasing engineering compromise, or pivot to uniflow.

The RTA decision

In 1983 Sulzer launched the RTA series with uniflow scavenging — a fundamental architectural pivot away from the company’s signature loop scavenging. The RTA:

• Used a single hydraulically actuated central exhaust valve in the cylinder cover (similar to B&W’s MC architecture)
• Permitted very long strokes (stroke-to-bore ratios up to 3.5+ in the largest variants)
• Achieved superior scavenging efficiency and trapping efficiency
• Enabled higher BMEP and lower SFOC than the preceding RND

The RTA series ran from 380 mm bore (5RTA38) to 960 mm bore (12RTA96) in its initial range. It was Sulzer’s mainstream product through the 1980s and 1990s.

RTA-T variants

Through the 1980s and 1990s the RTA series was extended with various variants:

• RTA-T: turbo-compound versions adding waste heat recovery
• RTA-X: long-stroke development versions
• RTA-2T: refined later versions

These variants kept Sulzer competitive with B&W’s parallel MC family but did not fundamentally change the architecture.

Post-1990 corporate restructuring

New Sulzer Diesel (1990)

In November 1990 Sulzer separated its diesel engine business as a distinct subsidiary, New Sulzer Diesel Ltd. (NSD). The reorganisation reflected the growing capital intensity of marine diesel R&D and the pressure on European builders from Asian shipbuilding consolidation. NSD remained a Sulzer subsidiary but operated as an independent business unit.

1997 sale to Wartsila

On April 1997 New Sulzer Diesel merged with Wartsila Diesel Oy of Finland and Diesel Ricerche of Italy to form Wartsila NSD Corporation (later Wartsila Corporation). Sulzer effectively divested its marine diesel business to Wartsila in this transaction. The exact transaction price was not publicly disclosed.

The 1997 sale ended 99 years of independent Sulzer marine diesel engineering. Sulzer Brothers itself continued to operate as a Swiss industrial firm in pumps, surface coatings, and turbomachinery, though without marine engine business. Sulzer AG remains today an active company in those other segments.

Engineering continuity post-1997

The Sulzer engineering team in Winterthur was retained largely intact through the Wartsila acquisition. The Winterthur facility continued as the design centre for the slow-speed two-stroke product line, now branded “Wartsila Sulzer.” Engine names retained the “RTA” prefix initially, with later “RT-flex” common rail variants.

RT-flex — common rail electronics (2001)

Engineering significance

In September 2001 the first commercial RT-flex engine entered service: a 6RT-flex58T-B installed on the bulk carrier MV Gypsum Centennial. RT-flex was the first commercial slow-speed marine diesel with common rail fuel injection and electronic control.

Compared to mechanically timed RTA engines, RT-flex offered:

• Variable injection timing in software (no mechanical cam changes)
• Multi-pulse injection capability for better emissions
• Cylinder-by-cylinder balancing through software
• Adaptive operation across loads and ambient conditions
• Better SFOC at all loads, particularly low-load (slow-steaming) operation

RT-flex anticipated the broader shift to electronic control across the marine diesel industry. MAN B&W’s parallel ME (Mechanical Electronic) family launched in 2003, also with common rail injection.

RT-flex96C

In 2006 the RT-flex96C was launched. The 14-cylinder version produced 80,080 kW output — at the time the world’s most powerful diesel engine in any application. RT-flex96C engines powered the Emma Maersk class container ships and other very large container vessels.

Continued development

Through the 2000s and 2010s, Wartsila continued RT-flex development. Subsequent variants (RT-flex96C, RT-flex58T, RT-flex68T-D, RT-flex35) were marketed as “Wartsila RT-flex” engines, retaining the Sulzer engineering lineage.

Transition to WinGD (2015-2016)

Joint venture

On 19 January 2015, Wartsila’s slow-speed two-stroke business was reorganised as Winterthur Gas & Diesel (WinGD), a joint venture with CSSC (China State Shipbuilding Corporation). At founding, CSSC held 70% and Wartsila 30%.

CSSC sole ownership

In June 2016, Wartsila divested its remaining 30% stake to CSSC, taking approximately a EUR 21 million write-down. CSSC has owned WinGD 100% since June 2016.

Engineering and product evolution

Under CSSC ownership, WinGD has:

• Continued the RT-flex series under the “X” product family designation (X35, X40, X52, X62, X72, X82, X92)
• Launched the X-DF dual-fuel low-pressure Otto-cycle gas variant (first commercial 2016 on SK Audace)
• Developed X-DF2.0 with iCER for reduced methane slip
• Announced X-DF-A (ammonia, first delivery 2025-26 on EXMAR vessels) and X-DF-M (methanol, first full-load running December 2024)

WinGD is the direct corporate and technical descendant of pre-1997 Sulzer.

Sulzer marine engine series chronology

Notable installations

Sulzer engines have powered thousands of merchant ships, naval vessels, and specialty craft over a century. Notable installations include:

• MV Monte Penedo (1912): 2 × 4S47 (one of the first sea-going 2-stroke motor ships)
• Various MAN-Sulzer twin-engine installations through 20th century
• Emma Maersk class (2006-): 14RT-flex96C-B, single 80 MW engine
• Modern container ships, tankers, bulkers: thousands of vessels with RTA, RT-flex, and (under WinGD) X-series engines

Engineering legacy

Sulzer’s engineering contributions to marine diesel are pervasive:

• Loop scavenging: defined two-stroke practice for half a century
• Uniflow conversion (RTA, 1983): enabled the very-long-stroke modern engine class
• Common rail (RT-flex, 2001): first commercial implementation in slow-speed marine
• Dual-fuel (X-DF, 2016): low-pressure Otto-cycle gas operation, distinct from MAN’s high-pressure Diesel cycle approach

Many of these innovations are now standard across the slow-speed marine diesel industry.

Service and spares

Engines built before 1997 are serviced through:

• WinGD for design support and OEM parts
• Wartsila Marine (which retains the QuantiParts spare-parts business) for legacy parts on Sulzer/Wartsila Sulzer engines
• Specialist spares houses for older RD/RND engines

Engines built after the 1997 transition (Wartsila Sulzer, Wartsila RT-flex, WinGD X-series) are fully supported by WinGD.

Related Calculators

• Engine Power Per Cylinder Calculator
• Brake Mean Effective Pressure Calculator
• Specific Fuel Oil Consumption Calculator
• Stroke-to-Bore Ratio Calculator

See also

• WinGD X-DF Dual-Fuel Engine Architecture
• MAN B&W ME-C Electronic Control Overview
• Two-Stroke Marine Diesel Engine Fundamentals
• Loop Scavenging Versus Uniflow Scavenging in Two-Stroke Engines
• Common Rail Fuel Injection on Two-Stroke Engines

Additional calculators:

• Marine Engine Model Decoder
• Pumps in Parallel or Series

Additional related wiki articles:

• Burmeister & Wain: History of the Copenhagen Marine Diesel Pioneer
• NOHAB and Polar Marine Diesel Engines
• Winterthur Gas & Diesel (WinGD) — Corporate History

References

• WinGD. (2024). Our History. Winterthur Gas & Diesel. https://wingd.com/about-wingd/our-history
• WinGD. (2024). Our Engine History. Winterthur Gas & Diesel. https://wingd.com/about-wingd/our-engine-history
• Sulzer AG. (Various years). Annual Reports. Sulzer Brothers Limited.
• Wartsila. (2002). First Sulzer RT-flex engine completes its first year. Press release.
• Wartsila. (2015). Wartsila and CSSC two-stroke joint venture starts operations. Press release.
• Wartsila. (2016). Wartsila to recognise write-downs in second-quarter results. Press release.
• Pounder, C. C. (Woodyard, D., ed.). (2020). Pounder’s Marine Diesel Engines and Gas Turbines (10th ed.). Butterworth-Heinemann.
• Sulzer Wikipedia history page: https://en.wikipedia.org/wiki/History_of_Sulzer_diesel_engines