.

Sail boats have had adjustable leeches for many years and any serious boat sailor would not consider sailing without the ability to tighten or loosen the leech as needed, so why not a windsurf sail?

Photo courtesy of Hansen Sails

By Jane Morson
Published: November, 2006

While most manufacturers of sails spend R & D time on the luff sleeve, battens and twist patterns of a sail, a bunch of friends, who are part of Hansen Sails, felt it was time to evolve.

Over the last few months the group has tried adjustable leech ideas, including a mechanical adjusting system, and although the mechanical system works, they felt they could do better. They looked at the details in the upper section of the sail. Now, Hansen is pursing a utility patent for the Hansen Compliant Leech technology (HCL), a development that provides a major improvement in sail performance by allowing a sail to automatically adjust its shape and twist according to the aerodynamic pressures encountered.

For windsurfing, HCL is particularly significant, because few changes to a sail’s tuning can be made, other than outhaul, which primarily controls draft in the lower sections of the sail. The overall shape and twist in the key upper sections are pre-set during rigging and cannot be controlled under way. Significant distortions are caused by the resilient bending of the mast under changing loads.

For modern truncated tip platforms, it is well known that the optimal twist and shape is highly variable depending on the course sailed and wind and water conditions. HCL solves these problems by providing a full shape with minimal twist which progressively flattens and twists off as the wind builds through the judicious placement of elastic flex panels in the sail body.

When in use, an HCL equipped sail automatically adjusts its shape in gusts and turbulent conditions, and as the sheeting angle varies during maneuvering and course changes such as reaching or running. In engineering terms, HCL matches the compliance of the sail to changes in aerodynamic force. The result is an effective moderation of the velocity squared aerodynamic forces and the relationship between sheeting angle and force. HCL provides a much greater time-averaged coupling of the sail to the wind for improved performance and handling.

In testing, notable improvements included low-end power and acceleration, upwind VMG, delayed stall, gust absorption and ease in handling while turning off the wind, jibing or water starting. HCL provides a wider range of effective sheeting angles and an extremely smooth ride which eliminates much of the fatigue associated with high-performance sailing.

In yachting, where rig motion in a seaway or turbulent air cause rapid shifts in velocity and sheeting angle, HCL provides immediate reactive micro-adjustments which are otherwise impossible due to the critical lag between input and active human response. The result is an average increase in drive per unit time, which is of use in either a competitive racing or cruising environment.

It’s exciting to note that certain aspects of HCL technology are also applicable to other aerodynamic or hydrodynamic devices.