Tuesday, November 11, 2008

Holy Billy Mays...That's a Big Propeller....

A heavyweight propeller, acting as a signpost to SMM 2008, was lowered onto its base on Thursday 18 September. It will be placed in front of the Central Entrance to the New Hamburg Fair, Messeplatz 1 (Germany).

Weighing in at nearly 58 tons, it will put the 47,000 or so trade visitors in the mood for SMM 2008. This leading industry event, the 23rd shipbuilding, machinery & marine technology international trade fair Hamburg, features 1,950 exhibitors from 55 nations, showcasing the latest technologies and products for shipbuilding and marine equipment at the Hamburg Fair site from 23 to 26 September.This modern fixed-pitch propeller with 5 sickle-shaped blades was built in Waren, Mecklenburg-West Pomerania, by Mecklenburger Metallguss GmbH (MMG), which is one of the world’s leading manufacturers of ship’s propellers and a supplier to shipyards around the globe. It is about in mid-range for MMG, with its diameter of 7.9 metres and weight of 57,760 Kg (2.2kg = 1 pound). After accomplishment of its mission as an SMM Eyecatcher, it will go into operation in a container ship having a capacity of 4,400 TEU (20-foot equivalent units). The ship is classified by Germanischer Lloyd and is being built at the South Korean shipyard Daewoo Shipbuilding & Marine Engineering Co., Ltd. (DSME). The main engine is a marine diesel type 8K90MC-C6 from MAN B&W, with an output of 36,540 KW to drive the propeller at 104 rpm. That is sufficient for an operating speed of 22.8 knots. In view of today’s fuel prices, shipowners attach more importance to fuel efficiency than to high maximum speed. The curving sickle shape of the five propeller blades is not a matter of design aesthetics, but is due to engineering considerations. The propeller skew, that is the dimension defining the blade arc geometry, is critical for vibration level caused by the propeller in the ship’s hull. More skew means less vibration.

The propeller is made of a special alloy, the main component of which is copper. Other elements such as nickel, iron, aluminium and manganese give the propeller the necessary properties such as high strength and elongation characteristics, and also resistance to seawater. Manufacture of propellers of this size may take about three months from the first drawing until they get their final polish. MMG can manufacture propellers with a finished weight of up to 140 tonnes and diameter 11.3 metres. That is enough for the largest container ships in service today. MMG has received numerous orders for propellers for 13,000 TEU container ships and for the new Post-Panamax class, said MMG Managing Director Manfred Urban, describing the company’s good order book. He added that MMG had received orders from Fincantieri, the leading cruise shipbuilder, for delivery of propellers for cruise vessels in construction for the well-known operator Carnival Cruise Line.

Ship’s propellers are naturally an important element in the chain of calculation, when trying to improve the fuel-efficiency of the large marine diesels – it is not just a question for the engine designers. At MMG the engineers have long since been working on new concepts, aimed at improving the efficiency of modern propellers, currently between 70 and 75%. “We are working on propeller shapes,” says Manfred Urban, “to improve efficiency and thus make a significant contribution to fuel savings. We are also optimising old propulsion concepts and optimising propulsion equipment so that it can still be profitably used.”These developments are possible thanks to modern calculation and simulation techniques. Designers have found, for example, that tanker propeller efficiency can be improved by reducing the number of blades, and that the well known disadvantages of a three-blade propeller can be minimised by optimising propeller geometries.

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