Ship propulsion

Marine diesel and LNG engines, wind-assisted ships and nuclear vessels.

Conversion and use · Transport systems · No. 115

• Conversion and use

The biggest ship engines are several storeys tall and among the most efficient heat engines ever built, topping 50%.

Chart: Illustration: Ship propulsion

Where it comes from

Chart: Map of where it comes from

Large ships use slow two-stroke diesels coupled straight to the propeller; big slow cylinders lose little heat. Heavy fuel oil supplied 79% of international shipping energy in 2018.

Three things to know

1. Only about 30% of a ship's fuel energy ends up pushing the hull, after engine and propeller losses.
2. A ship over 20 years old burns about 2.4 times as much fuel per container as one under five.
3. LNG engines that premix gas with air let about 6.4% of methane escape unburned, against 3.1-3.5% assumed in rules.

The journey

1. 1 Bunker fuelHeavy fuel oil, marine diesel or LNG
2. 2 Two-stroke engineHuge slow cylinders turn the shaft directly
3. 3 PropellerBronze blades turn torque into thrust
4. 4 HullThrust fights water friction, waves and wind
5. 5 Cargo movedContainers, ore and oil across oceans

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