Global shipping firms under pressure to cut carbon emissions are experimenting with an age-old technology: sails to harness ocean winds and reduce reliance on costly fuels.
"Five years ago, such projects would have gotten us thrown out by security" at shipping firms, said French naval architect Marc Van Peteghem.
"Now shipowners are listening to us," he said.
A design from his firm, VPLP, has just been picked by European rocket-maker Ariane Group for a sail-equipped cargo ship to transport parts for its new Ariane 6 launcher to French Guiana starting in 2022.
The ship will be equipped with four huge rectangular sails rising 30 metres (100 feet) high, supplementing a motor and cutting fuel consumption by about 30 percent.
It might not be the first, though: French start-up Neoline announced in July it would start building a sail-powered transporter this year for launch by the end of 2021.
"We have 5,000 years of experience in sailing with wind -- it's renewable energy, and less intermittent than solar power," Neoline's managing director Jean Zanuttini told AFP at his office in Nantes, western France.
So far the firm has orders from three clients, including French automaker Renault.
But using wind to meet carbon goals is not as simple as building new boats or rigging sails on existing ones, as some ship owners have already done.
"Our 136-metre ship costs 30 percent more than current ships," Zanuttini said, "but we compensate by using 80 to 90 percent less fuel."
Wind-powered vessels are also slower -- a hard sell for some shipowners and clients who want their raw materials and merchandise to move as quick as possible.
- 'Everything's in transition' -
Operators of the 60,000 to 90,000 oil tankers, bulk carriers, ferries and other huge cargo ships plying the seas are racing to find alternatives to fuel oil as pollution rules are tightened.
The industry generates roughly three percent of Earth-warming greenhouse gas emissions worldwide, a figure that experts say could reach 17 percent by 2050 if nothing is done.
Also, starting January 1, levels of air-polluting sulphur in marine fuel must be below 0.5 percent, according to new International Maritime Organization standards -- a sharp drop from today's 3.5 percent.
This is forcing firms to seek out cleaner, more costly fuels or invest in "scrubbers" to filter sulphur out of smokestacks.
"Everything is up for grabs, everything is in transition," said Gavin Allwright, secretary of the International Windship Association in London.
This month his group organised a wind conference at the Royal Institution of Naval Architects in London, just a stone's throw from Trafalgar Square and its statue of renowned British naval officer Horatio Nelson.
Even if sailing goes back centuries, "the vast majority of the technologies are 21st-century technologies and materials. They are almost fully automated, one-button computer operated," Allwright said.
Beside sails, some firms have designed huge kites that pull cargo ships, though just a few operators have adopted the system.
- 'Opportunity' -
Another option is to use "Flettner rotors" like those built by Norsepower of Finland, employing a technology developed by German engineers in the 1920s.
The tall columns are installed on a ship and set spinning, creating lift that propels a ship forward when they catch a perpendicular wind.
Ville Paakkari, a Norsepower representative at the London conference, said the columns can be installed in just a few hours, and can cut fuel consumption by five to 10 percent.
"The investment pays off in three to eight years," he told participants.
So far, Norsepower's rotors are used on just two cargo ships and the Viking Grace ferry between Finland and Sweden.
But wind advocates say tighter pollution rules -- potentially including more widespread taxes on carbon emissions -- will force shipping firms to clean up their act.
"People only change when they are forced to," Van Peteghem said.
"We need to find solutions so that what shipowners consider a constraint today will become an opportunity, and make them want to change," he said.