It may seem a bizarre sight – a big modern cargo ship flying an oversized ‘kite-surfing’ sail.
But this scene could become commonplace on the world’s oceans as shipping firms battle to slash fuel bills.
Set flying when the wind is strong enough, and attached to the ship by thick cables, the sails can cut the amount of diesel a vessel burns by as much as 20 per cent.
Maritime shipping each year pours out about a billion tons of the gases linked to global warming.
Cargo ships with 10,000sq ft sails could be introduced in a bid to battle rising fuel bills
In an innovation that promises to reverse the 19th Century moment when steam engines replaced wind power, sails currently in development will ultimately unfurl to as much as 10,000 square feet to pull giant vessels up to 1,000ft long through the waves.
One system is already in use, created by German company SkySails. Its sail – seen fitted to a 430ft cargo vessel in our picture – can unfurl to 90ft wide.
With its long cables giving it access to the stronger winds hundreds of feet up, it can achieve the power equivalent of an airliner, leaving a ship’s 20ft-high engines idle.
French company AirSeas has designed a similar fully automated system that unfurls at the push of a button.
The SeaWing is attached to large ships by a 1,200ft cable and is partly inspired by kite-surfing.
It has been suggested that when the wind is strong enough it could cut the amount of diesel a vessel burns by 20 per cent
The engineers who developed the SeaWing system are all employees of aircraft manufacturer Airbus, and AirSeas CEO Vincent Bernatets said: ‘They looked at the automatic technology of take-off and landing in an aircraft and thought, “Why aren’t we developing technology like this for a sail on a boat?’
Computers on board will take the vessel along the best routes for wind and fuel efficiency.
AirSeas have recently tested a smaller kite on a cargo ship between the Bay of Biscay and England. Mr Bernatets said: ‘We are in good shape. We are now analysing the results, but for the time being we are confident.
‘At the end of this year we will be able to take the final decision to launch or not.’
Kite-sail makers calculate that ship owners buying the systems will get the cost back within two years through fuel savings.