Downwind sailing gets a lift

From Ocean Navigator #143
January / February 2005
At first glance the sail looks like a spinnaker tearing itself apart, as if a radial split has opened and the torn fabric is bulging downwind. But, in fact, the Parasailor2 sail from a German company called Istec, is a novel approach to a downwind sail that incorporates elements of skydiving technology in a bid to reinvent the powerful – but not always easy to use – spinnaker.

The Parasailor2 is built with a substantial opening or slot across the middle of the sail. Spanning this opening, like a slat in a Venetian blind, is a fabric “wing,” the same type of soft airfoil wing used by skydivers for highly maneuverable descents. Once you get used to the unusual look of the sail, you start to see the benefits of this “eyebrow spinnaker.” The unusual sail was conceived by German sailor Hartmut Schädlich who also worked with Istec on the product development effort to turn the idea into an off-the-shelf product.


Air particles fill the belly of the Parasailor2 before rushing out the slot. This flow of air across the fabric wing creates both forward drive (1) and upward lift (2), producing the resultant force in red. The lift is also said to reduce the force on the masthead (3).

According to Istec, compared with a traditional spinnaker, the Parasailor2 provides sailors with a range of advantages, from increased performance to added safety and comfort. And Istec claims, the Parasailor2 can play the role of both a standard spinnaker and a gennaker.

The effect of the wing on the Parasailor2 is due to the interplay of the forces between the slot and the wing, both of these elements are necessary for the sail to be effective. As any sailor who has flown a chute knows, the pressure buildup on the weather side of the sail is substantial, especially as you head farther off the wind. What Schädlich and Istec have done is make use of this high-pressure air. The slot in the sail directs a jet of pressurized air across the fabric wing. This airstream “inflates” the wing, and it assumes an airfoil shape. According to Istec, the foil not only provides forward drive, it also creates lift that works to change the forces normally exerted by a spinnaker. Horizontal force on the head of the sail is decreased, and this means the masthead is more stable and there is less pressure on the bow. In addition, the inflated wing acts as a lateral support, stabilizing the sides of the sail and reducing the tendency for them to collapse.

Istec claims the sail increases performance because one sail can be used in wind angles from 70° to 180°. The company also claims that by relieving pressure on the bow and via the stability the sail imparts, a vessel’s rudder is more effective and fewer rudder adjustments are required. This means less work for a crewmember who is hand-steering, as well as less strain and electrical power needed by an autopilot.

For voyaging sailors who may be hesitant to use a spinnaker due to the perception that it increases rolling, yawing, pitching and the possibility of a flat-out broach, Istec claims the Parasailor2 actually reduces the problem of instability caused by a big kite of a sail imparting large forces on the top of the mast. The lift from the wing stabilizes the sail forces, and the slot acts as a pressure overflow valve; excess air from gusts is dumped out through the slot.

While voyaging sailors often are eager to embrace products that make voyaging easier, they also demand gear that is reliable and tough. Some voyagers might be skeptical of the Parasailor2’s durability given its open slot and the many support lines that make up the integral wing. On the other hand, Istec claims that German ocean sailor Bobby Schenk used the Parasailor2 on at least one extensive offshore trip.

Schädlich, the developer of the Parasailor2, was an active paragliding pilot and sailor when the idea for the Parasailor2 occurred to him in the 1990s. After working on the concept, by 1999 he had obtained a patent on the idea. One of the areas that required fine tuning was the profile of the wing that would be used. Schädlich and Istec invested considerable time optimizing the wing profile. They drew on extensive specialist knowledge from the sailing, paragliding and kite-surfing communities.

Image Credit: Images courtesy Istec

The wing structure is supported by a series of thin lines adhered to the leeward side of the sail. The durability of these lines could be an issue for long-distance voyagers.

They started with a wing profile typical of paragliders, one that was designed to produce lift but was also to reduce drag as much as possible – thus making the wing optimum for gliding. The Parasailor2 developers, however, were not as concerned with drag. They wanted a wing that produced substantial lift. The result was the wing used in the Parasailor2; it has a thicker cross section than the wing on the paraglider and is built with permanently deployed flaps. This downward-curved shape on the trailing edge of the wing and the larger cross section help the integral wing produce plenty of lift. This added lift produces added forward thrust and relieves the strain on the masthead and bow.

To aid in deploying and retrieving the Parasailor2, Istec also markets a spinnaker snubber called the Istec Sock. This product is similar to established spinnaker socks on the market, such as ATN Inc.’s Spinnaker Sleeve.

Time will tell if the Parasailor2 is seen as merely another interesting development in the sailmaker’s art, or if it becomes a valuable contributor to the ocean voyager’s holy grail: the fast, relaxing downwind passage.

Istec claims the sail increases performance because one sail can be used in wind angles from 70� to 180�. The company also claims that by relieving pressure on the bow and via the stability the sail imparts, a vessel’s rudder is more effective and fewer rudder adjustments are required. This means less work for a crewmember who is hand-steering, as well as less strain and electrical power needed by an autopilot.

For voyaging sailors who may be hesitant to use a spinnaker due to the perception that it increases rolling, yawing, pitching and the possibility of a flat-out broach, Istec claims the Parasailor2 actually reduces the problem of instability caused by a big kite of a sail imparting large forces on the top of the mast. The lift from the wing stabilizes the sail forces, and the slot acts as a pressure overflow valve; excess air from gusts is dumped out through the slot.

While voyaging sailors often are eager to embrace products that make voyaging easier, they also demand gear that is reliable and tough. Some voyagers might be skeptical of the Parasailor2’s durability given its open slot and the many support lines that make up the integral wing. On the other hand, Istec claims that German ocean sailor Bobby Schenk used the Parasailor2 on at least one extensive offshore trip.

Sch�dlich, the developer of the Parasailor2, was an active paragliding pilot and sailor when the idea for the Parasailor2 occurred to him in the 1990s. After working on the concept, by 1999 he had obtained a patent on the idea. One of the areas that required fine tuning was the profile of the wing that would be used. Sch�dlich and Istec invested considerable time optimizing the wing profile. They drew on extensive specialist knowledge from the sailing, paragliding and kite-surfing communities.

They started with a wing profile typical of paragliders, one that was designed to produce lift but was also to reduce drag as much as possible &mdash thus making the wing optimum for gliding. The Parasailor2 developers, however, were not as concerned with drag. They wanted a wing that produced substantial lift. The result was the wing used in the Parasailor2; it has a thicker cross section than the wing on the paraglider and is built with permanently deployed flaps. This downward-curved shape on the trailing edge of the wing and the larger cross section help the integral wing produce plenty of lift. This added lift produces added forward thrust and relieves the strain on the masthead and bow.

To aid in deploying and retrieving the Parasailor2, Istec also markets a spinnaker snubber called the Istec Sock. This product is similar to established spinnaker socks on the market, such as ATN Inc.’s Spinnaker Sleeve.

Time will tell if the Parasailor2 is seen as merely another interesting development in the sailmaker’s art, or if it becomes a valuable contributor to the ocean voyager’s holy grail: the fast, relaxing downwind passage.

By Ocean Navigator