Growing interest in ultra-long-stroke engine

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NOVEMBER 27, 2012 — MAN Diesel & Turbo reports a "healthy interest" in its ultra-long-stroke G-type engine and steadily growing orders. Most recently, Piraeus-based Polembros and U-ming of Taiwan have placed orders for a further six engines, bringing the current number of G-type orders up to 70 just one year after being available on the market.

The six recently ordered MAN B&W G70ME-C9.2 engines are all destined for 186,300 dwt Capesize bulk carriers and will be manufactured by China's CSSC-MES Diesel Co. Ltd. (CMD). The first of the six  is scheduled for delivery in December 2013 with the remaining five due during 2014. The vessels will all be built at Shanghai Waigaoqiao Shipyard (SWS).

MAN Diesel & Turbo has released figures comparing the performances of an 6G70ME-C9.2 type and a 6S70ME-C8.2 type aboard a Capesize bulk carrier – the latter engine represents a traditional choice for  a Capesize. Results show that the G-type engine makes a significant 6.5% saving in comparison to the S-engine, of which 4.5% stemmed from the improved propeller efficiency – which is a consequence of the lower rpm – and 2.0% from the actual engine. The following table contrasts the same engines’ key values:

man table

The G-type programme entered the market in October 2010 with the entry of the G80ME-C9 model. MAN Diesel & Turbo subsequently expanded the ultra-long-stroke programin May 2011 with the addition of G70ME-C9, G60ME-C9, G50ME-B9, G45ME-B9 and G40ME-B9 models. The G-types have designs that follow the principles of the large-bore, Mark 9 engine series that MAN Diesel & Turbo introduced in 2006. Their longer stroke reduces engine speed, thereby paving the way for ship designs with unprecedented high-efficiency.

Tankers and bulk carriers have traditionally used MAN B&W S-type engines with their long stroke and low engine speed as prime-movers, while larger container vessels have tended to use the shorter-stroke K-type with its higher engine speed.

Larger container vessels, in recent years, have also been specified with S80ME-C9 and S90ME-C8 engines because of the opportunity they offer to employ larger propeller diameters. Following efficiency optimisation trends in the market, MAN Diesel & Turbo has also thoroughly evaluated the possibility of using even larger propellers and thereby engines with even lower speeds for the propulsion of tankers and bulk carriers

Such vessels may be more compatible with propellers with larger diameters than current designs, and facilitate higher efficiencies following adaptation of the aft-hull design to accommodate a larger propeller. It is estimated that such new designs offer potential fuel-consumption savings of some 4-7%, and a similar reduction in CO2 emissions. Simultaneously, the engine itself can achieve a high thermal efficiency using the latest engine process parameters and design features.

MAN Diesel & Turbo has previously compared its 7S80ME-C9.2 engine with a G80 engine installed aboard a 319,000-dwt VLCC, where the G80 engine had a greater efficiency of 1%. Assuming optimum running conditions, including an optimum propeller set-up, the company found that propeller efficiency could be improved by about 3.6%. Under the same ship-speed conditions, overall running costs could accordingly be reduced by 4.6%, a significant saving that the company’s own figures suggest can even be bettered, depending on individual circumstances. Again, under the same ship-speed conditions, the EEDI would be reduced by some 8.2% when using the G80 as opposed to an S80 engine.

The G80’s longer stroke results in a lower rpm for the engine driving the propeller: a reduction from 78 rpm for the S80 engine to 68 rpm for the G80. This lower optimum engine speed allows the use of a larger propeller and is, ultimately, significantly more efficient in terms of engine propulsion. Together with an optimised engine design, this reduces fuel consumption and reduces CO2 emissions.

MAN Diesel & Turbo believes that, just as MAN B&W S-engines became first choice for containerships, G-engines will become first choice for bulkers, tankers and some box ships.

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