UK Sailmakers uses very powerful 3-D CAD/CAM software for sail design, which create virtual 3-D molds that can be digitally sliced into two-dimensional panels that when joined back together re-create a full-size version of the designed mold. Thanks to powerful 3-D graphic renderings, designers can see how a sail fits around the spreaders and shrouds as well as making sure the clew height and sheeting angles are right. They can also analyze how a main and genoa work together to make sure the boat stays balanced. The ultimate objective is a sailplan and sail shapes that put the maximum driving force in precisely the right place to produce a perfectly balanced boat – and with the least amount of drag.
Pat Considine, UK Sailmakers’ chief designer, goes a step further and uses Fluid Structural Interaction software, called FSI for short, as a virtual wind tunnel for refining sail designs and sail construction. FSI calculations are used to test proposed designs and cloth choices to make sure they are not built too strong (too heavy) or too weak (too light) for their expected loads. The FSI calculations will predict whether a sail’s design and construction will keep its shape properly as the rig bends, halyards are tightened, and sheets are trimmed.
Shown rotating in this video are two renderings of a Tripp 47 mainsail design. The side-by-side comparison shows the sail with no backstay tension and with max backstay trim. The FSI software allows Pat to rotate the two designs together to study their shape from any angle. In this case, Pat needed to be sure the draft would not move too far aft as the sail was flattened; likewise, he had to make sure the draft was not too far forward when the backstay was eased completely. The FSI program makes extremely accurate predictions of how specific sail designs will perform once made and trimmed in a variety of wind speeds. These tests ensure sails will meet the performance needs right out of the bag.