Efficient propulsion - The Triple-E two propeller system

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.

Triple-E: Efficient propulsion

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.

Facts

  • 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 tonnes, 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 tonnes, horsepower 43,000 and consumption 168 grams bunker oil per Kilowatt hour produced.