Sobstad first marketed Airframe sails in 1985, and the sails were used to win the America's Cup in 1987. Those early sails were a far cry from the sophisticated, highly engineered products that are now being manufactured, but they were a breakthrough for their time. The problems associated with paneled sails, namely bias stretch and hard angles in the catenary path were overcome by the Genesis method, which orientated individual yarns directly along specific load paths. The process starts by creating complex stress maps that analyze the various loads in sails and then reproduces the resulting two-dimensional stress map as a three-dimensional sail.

Strictly speaking, Genesis sails are not created on a mold, but manufactured in large panels, which are then pieced together to create the finished sail. In fact, in the case of Genesis sails, the seams where the panels come together are used to create the shape of the sail just as broadseaming is employed in panelled sails. Still, any sail that is designed and built using a three-dimensional design program can be referred to as a molded sail, and is certainly considered to be such by the U.S. court system. As part of its process, Sobstad has developed an interesting seam construction that allows two panels to be joined together without the need for sewing. This is important since in contrast to panelled sails where the various scrims and weaves provide plenty of yarns for the stitches to bite into, the Genesis panels have fewer yarns and the result is a seam that is much harder to sew. During the assembly process the Genesis seam is heat-sealed at 120 degrees Fahrenheit, while pressures on the order of 25 pounds per square inch are brought to bear on the seam. This heat, combined with pressure and the latest epoxy adhesives, results in a seam that does not need stitching, yet is still extremely strong (Figure 5.2).

As is the case with laminated fabrics, molded sails would not be possible without the sophisticated adhesives that have been developed in recent years. And it's important to remember that a large part of the success of the laminating process stems not only from the adhesive, but also from the amount of pressure that is applied to the surfaces being laminated. When rolls of sailcloth are laminated, for example, the pressure is exerted over a relatively narrow surface area. As soon as the surface area to be laminated is increased, say on a large mold, it is not that

Figure 5.2

Cross-section showing the Genesis seam, which uses heat, pressure, and adhesives to create an extrememly strong seam that does not need stitching.

The Genesis seam, heat sealed at 120 degrees Fahrenheit at 25 pounds per square inch pressure for maximum strength.

A typical sewn seam.

Epoxy adhesive and primary fibers.

Pressure-sensitive flexible adhesive.

Sewn seam hole elongation and movement under load.

3DL sails have become a common sight on the racecourse since North Sails geared up their manufacturing facility.

easy to get the intense pressure needed for a secure bond and more reliance is placed on the adhesive. In fact, there is an ongoing debate among sailmakers who produce paneled sails versus those that produce sails on a mold. The paneled sail-makers claim that their sails are actually lighter than molded sails because they are able to bring more pressure to bear on the fabric and therefore use less adhesive. It's an interesting debate that likely has no resolution since sails are complex pieces of engineering with too many variables to compare one technique directly against the other. It does, however, give the salesmen some interesting material for bringing in customers, and the difference in weight, if indeed there is one, will likely diminish as the technique for molding sails becomes more sophisticated.

In terms of the specific production process, the construction of Genesis sails begins with the application of thread to a film substrate, which is accomplished by a thread-laying machine that is programmed with each sail's design information. The machine plots precisely the right density and type of yarn to create what Sobstad calls the "primary carrier film." Once this is done a second layer of fiber on film is created with the yarns orientated to accept all the secondary loads to which the sail might be subjected. Then the two layers are bonded together to produce a strong panel ready for shaping and joining with the rest of the panels to finish the sail. As noted above, the individual yarns do not run the full length of the sail, since they are severed at each seam. But the design program lays them onto the film so that the seams from different panels will meet head-on creating a "virtually" continuous fiber running from head to clew. With no seam slippage and a myriad of yarns precisely oriented to accept the loads, the result is a sail designed to hold its shape once the forces of the wind come into play.

It's also important to note that with this kind of construction there is less need for the corner reinforcement usually found on paneled sails since the individual yarns radiating from the corners along the load paths efficiently take up the extra burden placed on the corners of the sail. On some Genesis sails I have

3DL sails have become a common sight on the racecourse since North Sails geared up their manufacturing facility.

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