The use of the internal combustion engine in ships was introduced in the early 1900s, and the Royal Dutch Shell tanker Vulcanus (built 1910) was probably the first motorship.

One of the leading shipyards to design and build motorships was William Doxford at Sunderland in Britain. In 1906, the Doxford yard began planning the introduction of the internal combustion engine for ship propulsion. Work on a four-cylinder engine continued, and after further research and successful trials, Doxford installed the engine in the Swedish ship Yngaren, the first motor ship to be built in the Doxford yard. Because of its economy and relatively simple operation, the engine became a major success and the so-called Doxford Diesel was used in many ships. It was not the only make of diesel engine used in motorships but in those early years, it was among the most common. Doxford no longer exists. With several other reputable large marine engine manufacturers (mainly European companies) it was overwhelmed by ever-increasing costs of research and development, as well as the costs of building the engines and the growing competition. Today, the two major large-engine makers are MAN-Burmeister & Wain, and Wartsila-Sulzer. Asian shipyards construct these engines under licence from the manufacturers.

Most modern ships have a reciprocating engine (with pistons moving up and down, powered by heavy fuel oil) as their main propulsion unit. The pistons are linked to the crankshaft which rotates and is coupled to the propeller, either directly or via a gearbox.

The first passenger motorship to arrive in South Africa was the Japanese vessel Santos Maru that berthed in Durban in January 1926. Shortly after that, the famous Union-Castle Line that operated services between South Africa and Britain introduced their first motorship, Carnarvon Castle, paving the way for a further five mailships, seven smaller passengerships and 12 reefer ships, each powered by Burmeister & Wain engines.

Most other vessels on the South African trade were also motorships.

The advantages in using internal combustion engines rather than coal-fired steam engines include the following :

• The amount of stowage space for the fuel is far less than the stowage space required for an equivalent amount of coal. This means that more space is available for cargo and/or passengers, increasing the revenue-earning capacity of the ship..
• The range of the motorship is greater than that of the steamer. This means that the motorship needs to make fewer bunker stops on long voyages.
• Motorships are more environmentally friendly than coal-fired ships as far less carbon or sulphur emission occurs in a motorship than in a coal-fired steamer.
• Motorships are cleaner for those aboard – when coal-fired ships were bunkering, coal dust dirtied the decks. When coal-fired ships were under way at sea, much soot was emitted from the funnel(s).
• Because a motorship does not need stokers to keep putting coal into the furnaces or trimmers to level off the coal in the furnaces and bunkers, fewer crewmembers were needed on a motorship. The cost of operating a motorship was lower than the coal-fired steamer.
• Subsequent increased levels of automation reduced crew sizes. As the workload in the engineroom has been reduced, the watch system has been revised on most ships, and maintenance is often done by teams who join a ship for a limited period to do specific tasks, fewer engineering officers and ratings are required. This reduction of numbers of crew has also led to the reduction of catering staff. A turbine cargo steamer of the 1950s may have had 60 crewmembers, whereas a modern motorship of similar cargo capacity has around 20 crewmembers. Some even have as few as nine crewmembers.

The engineroom of a medium-sized motor tanker. Photograph : Robert Young

Maribo Maersk, one of the so-called Triple-E containerships owned by Maersk Line. These ships are among the most environmentally-friendly ships currently in service. Photograph : Captain Stuart MacAllister