Sail designer Doug Slocum explains how North’s computer software was used to design fast sails for the J/70 even before the first boat was built!
When Heather Gregg Earl and crew beat 89 other boats to win the inaugural 2013 J/70 North Americans, they used sails that had been designed and thoroughly tested before the first J/70 was even wet! And so did the boats that finished 2nd, 3rd, 4th, 6th, 7th and 8th. This sounds almost like science fiction because it certainly wouldn’t have been possible in years past. The old method of developing one-design sails required a lot of two-boat testing on the water to evaluate designs. That process took a very long time, and even if it eventually produced fast sails there was no guarantee that those shapes could be reproduced exactly or consistently. The sail designers and software experts at North developed a much better approach. They created a proprietary software package called North Design Suite™ (NDS). NDS allows the designers to ‘sail’ any boat virtually in an infinite variety of conditions, all from the friendly confines of their computer. This greatly expands the designers’ ability to test different sail shapes, sail trim settings and sail/rig combinations, and it allows them to measure the results very accurately. The NDS software tools were originally developed for North’s work with big boats and grand prix events like the America’s Cup and the Olympics. Over the past decade they have been used more and more for a larger cross-section of one-design classes. NDS is a comprehensive system of design programs that allow a sail designer, with a lot of hard work, to develop sails that are literally fast out of the box. Here’s a step-by-step look at how this technology is being used for one design classes, including the first (and fastest) J70 sails.
STEP 1: Build a model of the rig and boat. Using North’s Desman™ program, the sail designer creates a complete three-dimensional model of the spars and rigging. This model incorporates very detailed information such as the mechanical properties of the spars, standing rigging and the rigging attachment points.
STEP 2: Design sails and place them on the rig. Using the program Spiral™, the designer specifies a shape for each sail. This software defines the sail’s three-dimensional shape using a ‘molded’ surface that the sail panels will be laid on. This shape, which is created without any wind load, will be optimized in later steps.
STEP 3: Define the structure of the sails. Using the software module 3D Layout™, the designer selects a fabric and a panel layout. The structure of a sail is as important as its designed shape because the two must work in concert to achieve the ideal ‘flying shape.’
STEP 4: Calculate a pressure map for the sails. The designer uses Flow™ to introduce wind pressure over the sail’s three-dimensional mold and produce a pressure map of the sail’s surface (photo left). This pressure field is then linked to Membrain to show what effects wind pressure will have on the molded sail shape.
STEP 5: Apply the pressure map to the molded sail shape. Using Membrain™, the sail designer takes the rig and sail model developed in the first three steps and applies the pressure field from Flow. Membrain considers the specific sail fabric and panel layout, adds in windpressure, and shows how the sails and rig will deform when they are loaded.
STEP 6: Fine-tune the flying shape. Once the sails’ flying shape is tuned and trimmed in Membrain, the deformed (pressurized) shape is sent back to Flow. This shape is different than the (nonpressurized) shape that was created in Spiral, so Flow re-calculates a new pressure map which goes back to Membrain and is applied to the sails to get a new deformed shape. This process is called aero-elastic coupling. With North Design Suite, the computer keeps going back and forth between Membrain and Flow until there is no longer any change in Membrain’s sail shape.
Aero-elastic coupling works for evaluating many things – changes in sail shape, sail trim, rig tuning and almost every other sail-related variable. It can (and does) answer, for example, the age-old question, ‘Will I go faster and higher if I trim harder?’ Being able to sail and test a boat virtually has opened up new horizons for one-design sailmaking. Before the J/70 hull design was completed, for example, North designers had already created and tested many sail shapes. Subsequent two-boat testing and the success of North sails at the 2013 North Americans (7 of the top 8) confirmed that the NDS-designed shapes were fast, and consistent too.
In addition to the J/70, many other classes have benefited from virtual modeling and testing in North Design Suite, including the Viper 640, VX One, 49erFX, Etchells, A-Cat, J/24, J/88, Melges 24, Melges 20 and Moth. Variables tested include new panel layouts, changes in sail fabric, improvements in shape and the effect of variations in mast stiffness. Simply having a computer and a plotter/cutter is no longer sufficient for sailmaking today. That’s why North One Design has committed to software that will model, sail and test boats virtually (and very accurately!). This allows each North sail designer to test many more options than ever before, and to do it in much less time. The result is an ever-improving product for one-design sailors.