Large-bore engines are the flavour of 1961
The port side of the Sulzer main engine in ‘Seine Lloyd’ showing the control position
The June 1961 issue of 'The Motor Ship' was full of news of large-bore low-speed marine engines, which seemed to be causing an even bigger stir than dual-fuel (oil and LNG) engines are at present.
‘Large bore’, 50 years back, meant 80cm-plus, so not too far from today’s largest bores of 96-98cm (and yes, we know that a design exists for a 100cm-plus bore engine but its chances of actually being ordered look pretty slim in today’s climate). However, the power outputs fell far short of today’s norm.
It was the quest for higher powers that led designers to increase the bore size, with the industry demanding reliable power in the 20,000 to 25,000bhp range. The first tentative steps had been made in 1960 by B&W (now, of course, part of MAN) with an 840mm bore six-cylinder unit rated at 1,730bhp/cyl. Such were the advances in turbocharging technology in the space of a year that similar units were being delivered in 1961 rated at 2,100bhp per cylinder. In 10-cylinder format, as used to power a new Norwegian 51,300ton tanker, that took the output into the magic 20,000bhp-plus bracket. Higher powers were to come; Gotaverken had an 850mm bore engine in service, which the builder was confident could be uprated to 2,100-plus bhp/cylinder, thanks to its maximum indicated pressure of 9.75kg/cm2 (9.6bar), then an almost-unbelievable high.
Sulzer too was in on the act, with a 900mm bore engine. A six-cylinder version had just entered service in the cargo liner Seine Lloyd, the first large-bore engine non-tanker afloat. This was rated at 12,000bhp at 119rpm, though on testbed trials it had recorded 3,000bhp per cylinder at 130rpm. However, the honours at that time for the highest specific output went to Fiat, whose 900mm bore engine had attained, from a nine-cylinder version, 26,000bhp at 131.4rpm. This engine was to enter service in a tanker later in the year.
The editorial comment in the magazine, while waxing lyrical about these achievements, felt that the Diesel engine had yet to reach its peak of development, and powers of 30,000bhp could be expected from engines designed to be overhauled only once a year. What a pity the writers are not around today, where the reliable, clean, 100,000bhp engine is a reality.
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