SkySails wind propulsion system
Engine, hull and propeller design
More efficient engines are key to effective propulsion and therefore to fuel saving that ultimately saves money and promotes anti-pollution measures. The shape of a ship’s hull is important in determining how well she passes through the water in terms of resistance, while the size of a ship’s propeller and the shape of the propeller blades are major factors in determining the efficiency of propulsion. Much work has gone into the design of propellers and propeller blades to improve efficiency.
The following is an extract from the website http://www.maersk.com/en/hardware/triple-e/the-hard-facts/efficient-propulsion and relates to the remarkable design of the so-called Triple-E 18000-teu containerships belonging to Maersk Line.
Efficient propulsion – The Triple-E two propeller system
The Triple-E ship has greater fuel efficiency due to two-propeller system. Maersk Line’s Triple-E may be the world’s largest container vessel but it is no gas hog.
Designing a propulsion system powerful enough to move the ship through the water but with maximum fuel efficiency was a tough task. The secret of the vessel’s energy efficiency lies in its custom-designed ‘twin-skeg’ propulsion system, which uses two engines and two propellers. And the results are astounding: the Triple-E can transport 2,500 more containers than Maersk’s currently most efficient ships (E-class) – while using 20 percent less fuel and cutting CO2 emissions by 20 percent.
The top speed of the Triple-E was capped at 23 knots, two knots lower than that of E-class ships. This means it has a reduced power requirement of approximately 60 megawatts, a reduction of roughly 25 percent compared to the E-class’s 80 megawatts. Setting a lower maximum speed allows Maersk to use engines that can operate at slower revolutions – the ‘ultra-long stroke’ engine – which provides greater fuel efficiency. However, retaining the efficiency created by the slower revolutions of an ultra-long stroke engine re¬quires a propeller with a larger diameter.
This posed a problem for the designers: the size of the propeller – which has to be submerged – is limited by the ship’s draught, the part of the vessel that is underwater. Their solution was to adopt the twin-skeg system. The Triple-E’s two propellers are 9.65 metres in diameter, each fitted with four blades, compared to the single propeller of the E-class, which has a similar diameter but six blades. This gives the Triple-E a significant advantage: the combined diameter of its twin propellers provides greater pushing power in the water and the fewer number of blades creates less resistance.
The propulsion system of the Triple-E is set to revolutionize long-distance transportation. As a result, Maersk will be able to ship goods on the busy Asia-Europe route with an Economy of scale, Energy efficiency and huge Environmental benefits.
- Overall, the Triple-E has 16 percent greater capacity than an E-class vessel but is more energy efficient.
- The Triple-E is designed for lower speeds, using the lowest number of engine revolutions with the largest possible propeller diameter to achieve lower fuel consumption.
- The four-blade propellers, each weighing 70 tons, were manufactured by Mecklenburger Metallguss GmbH in Germany.
- Using fewer propeller blades on the Triple-E – four compared to six on an E-class vessel – results in a less wetted surface of the propeller and thereby lower resistance.
- The propellers took 10 days to cool after being cast in moulds and heated to temperatures reaching 1,190 degrees Celsius.
- The first propeller was transported by a Maersk Line container ship from Hamburg to the Daewoo shipyard in South Korea.
- The Triple-E uses a special ultra long stroke engine. This MAN Diesel engine operates with a lower number of revolutions compared to a traditional engine.
- Using two propellers requires two engines on a vessel, each with the following specifications: Weight 910 metric tons, horsepower 43,000 and consumption 168 grams bunker oil per Kilowatt hour produced.
More efficient fuels and improved marine paints
Much research has gone into improving the efficiency of marine fuels and to reduce the amount of carbon and sulphur emissions from the fuels.