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Low carbon innovations for maritime freight

Sailing merchant ships: utopia or reality?

Anaïs Marechal, science journalist
On May 4th, 2022 |
4 min reading time
Philippe Cauneau
Transport Engineer at the French Agency for Ecological Transition (ADEME)
Key takeaways
  • The International Maritime Organisation and the European Commission are demanding increasing decarbonisation efforts from shipowners, and sea freight is expected to be included in the EU Emissions Trading Scheme by 2023.
  • Several technologies exist for sail propulsion: the Flettner rottor, rigid composite panels, sails and notably the innovative kite.
  • One study estimates that 40-45% of the world fleet (37,000-40,000 ships) could benefit from sail propulsion by 2050, due to the lower cost of this technology and its wide availability.
  • Another study shows that 3,700 to 10,700 ships could be equipped with sail propulsion systems by 2030. This could avoid 3.5 to 7.5 million tonnes of CO 2 emissions by 2030.

Is sail­ing propul­sion a seri­ous option for reduc­ing the car­bon foot­print of mar­itime freight?

Since 2011, we have seen the emer­gence of projects for the use of diesel propul­sion in the mer­chant navy. And the cur­rent sit­u­a­tion – in par­tic­u­lar the very high cost of ener­gy – is increas­ing­ly favourable to the sec­tor. Wind is a source of ener­gy that is free from the prob­lems of spec­u­la­tion, secu­ri­ty, and infra­struc­ture. In addi­tion, the Inter­na­tion­al Mar­itime Organ­i­sa­tion and the Euro­pean Com­mis­sion are demand­ing increas­ing decar­bon­i­sa­tion efforts from shipown­ers, and sea freight is expect­ed to be includ­ed in the EU Emis­sions Trad­ing Scheme by 2023. 

The huge advan­tage of diesel propul­sion is its avail­abil­i­ty: it is an ide­al solu­tion in the short term, and com­ple­men­tary to alter­na­tive fuels in the longer term. There are already 15 ships in the world that are using sail propul­sion sys­tems. Some tech­nolo­gies are mature, such as Flet­tner rotors, and oth­ers will be test­ed very soon. For exam­ple, the Nantes-based start-up Airseas has been test­ing its kite since Decem­ber 2021 on a ship char­tered by Air­bus between France and the Unit­ed States. Zéphyr & Borée plans to launch its Canopée sail­ing car­go ship this year, which will trans­port the future Ari­ane 6 launch­er from main­land France to French Guiana.


You men­tion sev­er­al tech­nolo­gies: in con­crete terms, what is the nature of sail propulsion?

There is a real pro­lif­er­a­tion of inno­va­tions and tech­ni­cal solu­tions. The most mature solu­tion is the Flet­tner rotor, dis­cov­ered in 1924. Since 2010, the firm Ener­con has demon­strat­ed that this tech­nol­o­gy is com­pat­i­ble with the con­straints of mar­itime freight. The rotors need to be rotat­ed by means of anoth­er ener­gy source, a motor, or a huge fan in the case of suc­tion pro­files. Cur­rent­ly, oil-fired gen­er­a­tors are used on board to pro­duce this pow­er, and alter­na­tive fuels could be con­sid­ered in the future. 

There are also oth­er wind propul­sion tech­nolo­gies that use only wind pow­er. Con­ven­tion­al flex­i­ble fab­ric wings, such as those on old rigs like the three-mast­ed Belem, age quick­ly and are not very effi­cient. Today, shipown­ers are turn­ing to rigid pan­els, made of com­pos­ite mate­r­i­al, or thick pro­files that resem­ble an air­craft wing. 

All these sys­tems are locat­ed on the deck of the ship, and there­fore require space. One of the lat­est solu­tions explored is the kite: this time the wing is aer­i­al. This is quite inno­v­a­tive, and the tech­nol­o­gy is cur­rent­ly being developed.

Can all ships be equipped, and can we achieve 100% wind propulsion?

It is pos­si­ble to retro­fit exist­ing ships today. A study 1 esti­mates that 40–45% of the world fleet (37,000–40,000 ships) could be retro­fit­ted by 2050, due to the low­er cost of this propul­sion and its wide avail­abil­i­ty. Wind will in most cas­es be an aux­il­iary ener­gy source, part­ly reduc­ing the need for the ship’s com­bus­tion engine.

New ships will have to be built to achieve almost entire­ly wind propul­sion (they will still car­ry an engine to secure the port approach). This per­for­mance can only be achieved by ships designed for this pur­pose, and not by retro­fitting: their hulls must inte­grate anti-drift sys­tems linked to the use of sails, and the posi­tion­ing of the masts must respect the bal­ance of mass­es and access to car­go spaces by port ser­vices. The Neo­line sail­ing freighter, cur­rent­ly under devel­op­ment, will be equipped with four masts pro­vid­ing 90% of the ener­gy require­ment for its propulsion.


The heav­ier the ship, the more pow­er is need­ed to move it. Sail­ing propul­sion makes sense on medi­um-sized ships – up to 200 metres in length – at a speed of about 15 knots. By com­par­i­son, a con­tain­er ship can be up to 400 metres long and trav­el at 20 knots.

So, deploy­ing vee-propul­sion on a large scale will require a reor­gan­i­sa­tion of mar­itime trade?

Yes, the con­cept of mas­si­fi­ca­tion using con­tain­er ships and logis­tics hubs is out­dat­ed. Ship propul­sion address­es new tasks, such as the long-dis­tance trans­port of goods on inter­me­di­ate-sized ves­sels. They can call at more ports, espe­cial­ly sec­ondary ones: this brings the goods clos­er to the con­sumer and reduces pre- and post-car­riage, which is usu­al­ly done by road. Speed is also reduced: the Neo­line car­go ship will sail at an aver­age speed of 11 knots. This does not pre­vent ship­pers such as Man­i­tou and Beneteau from show­ing inter­est. It will be a vir­tu­ous logis­tics chain, and con­sumers must be involved by accept­ing longer deliv­ery times to avoid a rebound effect. 

Anoth­er change con­cerns the mode of nav­i­ga­tion. Wind propul­sion needs wind so some­times sea routes will have to be mod­i­fied to take advan­tage of it. To do this, crews can rely on mar­itime rout­ing – tak­ing into account the weath­er con­di­tions – which is essen­tial for sail­ing solu­tions. But shipown­ers are not used to this type of nav­i­ga­tion, and there is a psy­cho­log­i­cal brake. Final­ly, it should be not­ed that the propul­sion of sail­ing boats is more favourable on transat­lantic routes in the North, and less so on the route between Europe and Asia.

What is its decar­bon­i­sa­tion potential?

We do not know pre­cise­ly. A study 2 shows that 3,700 to 10,700 ships could be equipped with diesel propul­sion sys­tems by 2030. This could avoid the emis­sion of 3.5 to 7.5 mil­lion tonnes of CO2 in 2030. We can also rely on the esti­mate of the retro­fit poten­tial of exist­ing ships pro­duced for the UK gov­ern­ment (37,000 to 40,000 ships) 3: if 10% of fuel can be saved by the use of sail propul­sion, an over­all reduc­tion in con­sump­tion of around 3% is achieved. 

But the major uncer­tain­ty con­cerns the actu­al ener­gy gain of the sys­tems. There are no stan­dards for mea­sur­ing per­for­mance, only the man­u­fac­tur­ers pro­vide an esti­mate of the gain made by their solu­tion. On this basis, it is esti­mat­ed that the ener­gy gain asso­ci­at­ed with Flet­tner rotors is around 8%, up to 20% for the kite or even up to 30% for thick pro­files. But these are the­o­ret­i­cal mea­sure­ments: today we lack mea­sure­ments in nav­i­ga­tion as well as a stan­dard, such as an ISO norm. This is an impor­tant issue, which would enable shipown­ers to accu­rate­ly assess the return on invest­ment of these decar­bon­i­sa­tion solutions.

1Bell M. et al., Reduc­ing the mar­itime sector’s con­tri­bu­tion to cli­mate change and air pol­lu­tion, Eco­nom­ic oppor­tu­ni­ties from low and zero emis­sion ship­ping. A report for the Depart­ment for Trans­port, Fron­tier Eco­nom­ics, juil­let 2019, 51 p.
2CE Delft, novem­bre 2016, Study on the analy­sis of mar­ket poten­tials and mar­ket bar­ri­ers for wind propul­sion tech­nolo­gies for ships
3Bell M. et al., Reduc­ing the mar­itime sector’s con­tri­bu­tion to cli­mate change and air pol­lu­tion, Eco­nom­ic oppor­tu­ni­ties from low and zero emis­sion ship­ping. A report for the Depart­ment for Trans­port, Fron­tier Eco­nom­ics, juil­let 2019, 51 p.

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