Development of a dinghy Radial Cut Sails

North Sails is entering its 30th year making sails. Much has changed since the first sail designs were lofted on Lowell North's garage floor in San Diego.

When North Sails Japan began to produce a dinghy sails in 1973, the drawing of the real size of a sail was marked on the floor of sail loft, and sail cloth was arranged on it. The shape was placed at the edges of the panels by bending a wooden lofting rod to form a curve. Efforts to reproduce the same curves from one sail to the next was difficult. So at that time, there was some luck to get a good sail and much depended on the skill of the individual sailmaker.

There was improvements in accuracy in the early 80's as mylar patterns were used to recreate the actual panels of the sails. It was possible to reproduce a sail shape close to original and to make incremental changes to evolve the pattern. The downside of the mylar patterns was that the mylar is easily damaged and the pattern tape used on the edges shrank, causing some distortion from the original panel shape. It was also an art to develop the sail shape using a mylar pattern. While easy to change a broadseam on one edge of a panel, there was some guess-work as to how this would affect the curve of the other panel edges. and the 3 dimensional flying shape.

Some sailmaking skill was lost as it was easy to use an existing pattern with some changes than to loft a new sail design with all the trial-and-error involved.

Through the mid and end of the 80's, computer-aided design (CAD) began a revolutionary change in sail design, construction and knowhow. It was possible to perfectly re-create a sail design in either 2 or 3 dimensional form and to make accurate changes to specific characteristics by altering either the edge curves such as the luff curve to a mast bend or the built-in (moulded) shape. It became economical to customize sail designs for any sail with a reasonable expectation of success. A fundamental change in the philosophy of the sailmaker was to think of designing sails in 3-dimensional form as previously through the history of sail design it was only possible to relate to a sail design in 2 dimensions because of the lofting and cutting process.

Since North Sails Japan became involved with the sails of America's Cup, the tools used for sail design and evaluation evolved with epoch-making improvents in precision. The technology succeeded on all scales including the design of dinghy sails.
From the photograph analysis of a base model sail used with typical rig tuning, a proceeding sail model can be designed with some adjustment for specific sail shape outcomes. Typical environment variables are the designed windspeed or wave condition and mast stiffness with crew weight. With advanced "live" sail and rig modelling tools, the effect of change in sail design can be assessed in a variety of wind conditions and with any mast stiffness.
The sail control variables are exactly what you have available on the boat such as mast step position, rake, forestay tension, spreader settings, sail controls etc.
But in addition, we can also make changes to the mast inertias (fore-aft, sideways and torsional stiffness), batten stiffness, sail cloth specifications and trapeze wire weight (crew weight). By changing one control at a time it is possible to determine how this control affects other variables, such as how the cunningham on a mainsail affects the mast bend at various tensions.
With the cloth specifications as a variable, we can also calculate the growth of the sail as air pressure is applied to the surface. We can also map the surface deformations and load paths which enables us to find the ideal panel layout. In this way, determining the best design for any rig or set of conditions by computer simulation has become a reality.
Full-scale testing of the design and analysis system using a "live rig" has been ongoing since 2001 resulting in another leap of performance since adopting the "Radial-Cut" sail designs.

There are a lot of advantages of radial cut sails as follows.

1. Since it is a 3-Dimentional design by computer where the shape is transferred to the radial panels with very fine tolerances, there is no distortion and a smooth and beautiful curve is developed.

2. Factors such as sailing weight of a team, stiffness of a mast, and side bend, are inputted, and a perfect sail shape is obtained for the rig and crew weight used.

3. Since the optimal cloth is most effectively arranged according to the direction of the stress in a sail, the result is the shape being maintained over a wider wind range and for a longer period (longer racing life).

This design system and a radial cut brings you..
Sail shapes and mast matching the style of a specific team.
The stiffness of the mast to be used and the sail designed to a target shape can be analysed correctly in a short period of time.

The design and snalysis system has been used successfully by many national teams forming for the 2004 Olympic games.

While North Sails Japan design and analysis system has been developed working mainly in the 470 class, we have cloned the technique to other classes with equal success. You can now own "Radial-Cut" sails for Snipe and FJ class as we have various models for the rigs already in our extensive library.
Of course, optimized sails for any class can be made. For your yacht class or special rig please feel free to consult us.