Maersk cut fuel 30% by slowing its container ships to clipper speed

Container shipping's economics assumed speed: in the boom before 2007 the Emma Maersk, one of the world's largest container ships, burned about 300 tonnes of fuel a day and emitted around 1,000 tonnes of CO2. When the recession cut cargo and fuel costs bit, Maersk — the world's largest line, with more than 600 ships — chose to slow down.

The industry cut cruising speeds from 25 to 20 knots, and Maersk went further to 'super-slow steaming' at about 12 knots. The engines had to be adapted to run reliably at a fraction of their design output. The result, Maersk said, was a 30% cut in fuel consumption and CO2, and savings of more than £65 million on fuel by mid-2010.

The trade-off was deliberate: voyages take longer, so the line needs more ships to keep frequency, but fuel is such a large share of cost that the savings outweigh the extra vessels. Maersk's technology chief called slow steaming the most important factor in reducing the company's CO2 emissions in recent years.

Slow the ship; fuel falls faster than time rises

Fuel consumption falls faster than transit time rises

Engines could be adapted to run safely at low power

Extra ships cost less than the fuel they saved

Customers accepted longer lead times in a slack market

When a cost rises steeply with speed, the cheapest efficiency is to go slower — if your customers can wait, the whole fleet economics change.

Slow steaming became standard across the container industry, and by 2010 crossing times were comparable to the great age of sail. Maersk kept cutting emissions, targeting a 25% reduction by 2020, with slow steaming the main lever.