While sails and wings are both airfoils designed to produce lift, the differences between them are obvious. One is made of cloth while the other tends to be a fixed structure. A sail’s shape can be changed, it can be reefed to reduce its area and, if all else fails, it can be dropped to the deck. A wing gives you fewer options. Wings can produce substantial lift, however — witness their use on America’s Cup race boats. But what about inflatable wings, like those used in wing parachutes? Two sailors in Switzerland have introduced an inflatable wing sail that can be changed in shape and also be dropped to the deck like a cloth sail.
Called the Inflated Wing Sail (inflatedwingsails.com/en/), it’s the brainchild of Edouard Kessi and Laurent de Kalbermatten. The Inflated Wing Sail (IWS) is a symmetrical foil that is formed by air pressure. Battery-powered electric fans pump air into the inflated sail and are designed to stabilize its shape for various wind conditions. The sail rides on a stayless retractable mast.
Kessi co-owns the sail loft Voiles Gautier in Switzerland and is the co-developer of the 3Di three-dimensional sailmaking technology behind the black sails used by the Alinghi race team. That technology is now part of the North Sails group. According to the IWS website, in 2010 Kessi “developed the first hard multiple-filament composites and was the co-founder of North TPT. During these last years, he worked on the production of large inflated textile structures such as the inflated hangar of Solar Impulse, which sheltered the ultralight airplane during its world tour.” In the 1980s, Kessi worked on developing the modern paraglider and worked in the inflatable textile industry for 15 years with the company Ailes de K, which he co-founded with de Kalbermatten. He’s an active sailor in monohulls and multihulls and is the record holder of the Lake Geneva Bol d’Or.
The IWS with its distinctive tufted leech.
De Kalbermatten is a longtime pilot in fixed wing, helicopters and hang gliders. His and Kessi’s company Ailes de K manufactured the first industrial paraglider, called La Randonneuse, which was popular worldwide. As told on the IWS site: “In 1999, he invented a new concept of wing by marrying an inflated paraglider wing to a horizontal mast. The ‘Woopy wing’ was born. Even today, it still flies in hang gliders, ski gliders, ultralight aircraft and even as unmanned aircraft. Two years ago, Laurent and Edouard Kessi joined forces again and, by sharing their respective flying and sailing competences, tested the Woopy wing vertically on a yacht. The new concept was a success and led to the birth of the IWS.”
The IWS idea takes the horizontal Woopy wing and makes it vertical. Along with the inflatable wing concept, the two Swiss sailors also developed a retractable mast that fits inside the inflatable sail. Thus, the entire rig compacts into a small package with no mast extending high above the boat. Another aspect of the inflated sail’s retractable mast is the lack of any standing rigging. Like other freestanding rigs, there are no shrouds or fore and aft stays, no chainplates, no turnbuckles and no other deck gear associated with a traditional rig.
When asked about the impetus behind the inflatable sail, Kessi replied via email that the goal was to apply the advantages of the Woopy wing to sailing, “to have a soft wing rig with a telescopic mast that gives all the advantages described in our presentation [on the website].”
According to the inventors, the IWS provides the following advantages:
The IWS sail performing in heavier winds.
• The sail flies vertically.
• The NACA airfoil has been studied to develop a high driving force for a low righting moment.
• Using a symmetric airfoil allows for tacking from one side to another without having to trim the sail shape.
• The symmetric airfoil is balanced and places itself in the best position to maximize the driving force.
• The aerodynamic center stays stable in every wind condition.
• This kind of sail can easily be driven by an automatic system.
Further advantages claimed for IWS include the elimination of battens and deck hardware and the control of sail shape by changing the internal air pressure. The IWS site claims the IWS system would be suitable for cruising sailors.
When asked by email if the IWS was suitable for heavier winds, Kessi replied, “We have already sailed on Lake Geneva for two months and sailed in wind conditions up to 25 knots with two reefs and retracted mast.”
Would the IWS be something that voyaging sailors would use? Probably the biggest questions the IWS would have to answer with cruisers would be issues of cost, reliability and durability. If the retractable mast system fails to retract, how easy would it be to get at the mechanism to repair it? Plus, since the sail has to hold pressure to inflate, how durable is the fabric and how easily is it patched? To be fair, these are also questions for traditional cloth sails. While the inflatable sails don’t seem like something most voyagers would quickly embrace, IWS is an intriguing concept that might garner some traction.