New toy

Naval architect and Americašs Cup performance- analysis consultant Claudio Fassardi has recently launched a new real-time sail shape measuring system that he has developed in partnership with electronics engineer and fellow San Diego resident Tomas Godoy

Introduction
In simple terms the ability of a sailboat to sail quickly depends on the ability of its hull to develop low resistance when moving through the water and of its sails to deliver maximum forward thrust. The ability of a sail to deliver maximum forward thrust depends mainly on its design. The improvement of sail design has been the objective of sailors since man first set foot on sail-assisted ships. Back then improvements in sail design, along with improvements in rig configurations, produced faster and more manoeuvrable ships that generated higher profits to commercial shipowners and provided tactical advantages to naval ships.

Since the Industrial Revolution, when power-assisted ships displaced sail-assisted ships in every commercial and naval activity, propelling a vessel by means of sails has essentially being confined to pleasure sailboats. While speed is still a desirable feature for a sailboat to have, it is essential for raceboats. From all the factors involved, sail design is a critical factor in the equation for achieving maximum performance.

Sails are made of stretchable materials that make them deformable under wind loads. In addition, a variety of rig controls allows for the change of sail shape to maximise performance over a range of conditions. The undeformed sail shape is known by the sailmaker; however, commonly known as the flying shape, the shape that the sail adopts under the wind load, rig and sail adjustments made during sailing are essentially unknown and difficult to predict. So the thrust a sail can produce is not accurately known. Knowledge of the flying shape of a sail is important to those involved in the design of performance sailboats. It is important to the sailmaker because the deformation process of the sail could be better understood and desirable flying shapes could be better achieved from the undeformed shapes. Better knowledge of flying shapes will always allow analysts to produce more accurate aerodynamic models for the prediction of performance with Velocity Prediction Programs (VPPs). Finally, this knowledge is important to the sailor because, in conjunction with knowledge of the corresponding sail/rig adjustments and the various performance parameters measured by onboard sensors, it permits better understanding of the effects of sail trim. The prevalent technology for surveying flying shapes comprises the tedious and time-consuming process of acquiring images onboard, and analysing them ashore afterwards with special image analysis software...

To read the remainder of this and many other articles, please purchase your copy of the April 2007 edition of Seahorse International Sailing available at selected newsstands or by calling: + 44 (0) 1590 671899 or by email at: info@seahorse.co.uk

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