Parasailor ²

The Assignment

The project Parasailor² shows that product optmization and innovation have no boundaries. At the beginning of 2003, RGD™ received the assignment to develop a novel downwind sail for the ISTEC AG. It was intended to be the safest and most efficient sail yet.

A downwind sail – also called a spinnaker – is an especially large, roundly cut sail out of a lightweight material, which leads to an enlargement of the sail’s surface and therefore also to increased performance and speed. A drawback of the standard spinnaker construction is the concentrated and abrupt bursts of captured energy. With large spinnakers, incoming gusts or waves can raise the horizontal energy so much that the rudder is no longer able to keep the boat on course. The result is a dangerous loss of control.

In order to avoid this drawback, RGD™ took the patented idea of sailor Hartmut Schädlich and combined paragliding technology with the physics of sailing. The product was Parasailor², a symmetric spinnaker with a broad opening in the upper half of the body of the sail. In front of this opening is a special miniature wing, which is filled by means of dynamic pressure – similar to a paraglider. This wing generates aerodynamic buoyancy and propulsion. The energy is transmitted over lines to the main sail, which gives it a greater degree of stability, thereby ensuring safer and more efficient movement for the boat.

The Challenge

The physics of the movement of fluids around flexible elements – such as sails – is highly complex. A sailboat is always susceptible to outer variables, such as high waves and currents. In addition, the wind speed is never constant and is influenced by surface friction.

The combination of these two different systems – that of the sail, and that of the wing – increases this complexity. The interaction of several overlapping systems is the most difficult challenge of all in the world of sailing. With this system combination, the number of variable parameters is nearly unlimited, which confounds even the most modern analyzing software.

The Execution

The basis of the development process for Parasailor² is the body of the main sail. In combination with the wing, its form interacts completely differently than a spinnaker with a standard cut. The air intake position of the wing, as well as its profile and form, define the characteristics of the sail and thereby its range of implementation.

Variations on these parameters significantly alter the entire product. That is why it was all the more important for RGD™ to find a homogenous compromise between performance and handling characteristics. Several experimental models were necessary in order to ascertain the working limitations.

Only by means of their profound expert knowledge in the fields of aerodynamics, construction of flexible airfoils, and CAD construction was it possible for RGD™ to prepare these experimental models. With the help of sailing enthusiasts and professionals, comprehensive product tests were performed, and the various sizes of Parasailor² were able to be delivered for production.

Project Details

What makes Parasailor² so unique?
This spinnaker provides sailors with a performance range and level of safety that was previously considered to be impossible. The venting function of the opening leads to an excellent release for gusts of wind, since it provides an escape for excess air; and at the same time buoyancy is generated in the wing. Moreover, the construction of the integrated wing allows a proper balance between buoyancy and propulsion. This decreases the horizontal energy that attacks the head of the spinnaker as well as the resulting torque on the mast. The bow is also considerably relieved. Rolling and swerving are drastically reduced.

Through the inner dynamic pressure, the wing part of the Parasailor² functions as a cross-bracing and stabilizes the leeches. This allows for a much flatter sailing profile, which gives the Parasailor² a performance range from 70 to 180 degrees to the direction of the wind.

Rolling and swerving, as well as the movement of the ship, have been the main risks when sailing with a spinnaker up until now. Rough seas combined with gusty winds could lead to the loss of the spinnaker, or in the worst case to the loss of the entire rig, even with an experienced crew.