The re-examination of IOR yacht performance - obtaining data for velocity prediction and sensitivity to data accuracy and quality

Abstract

The International Offshore Rule (IOR) provided a handicap system for racing yachts in the 1970s, 80s and 90s. It was accepted worldwide and many of the famous yacht designers of today made their name in the high profile events that took place under this rule. There is a large body of commentary and opinion regarding yachts of this era, in which the rule allowed the designer to explore the design space in search of designs that rated lower than their size. Yachts, particularly in the early IOR era, were designed through experience, knowledge of the rule and inherent talent. Computing power was low and the subject of velocity prediction was in its infancy. This paper examines a method of undertaking a velocity prediction of yachts of this era using data provided by the designers, namely lines plans and rating certificates. A performance sensitivity analysis is conducted examining aspects such as measured versus sailing trim, lack of geometric data, influence of waves and sail configurations. The results show that subtle changes in input data, associated with the yacht, can be measured in terms of performance. This will allow for the future comparison of fleets of boats and provide some data to confirm or contradict the sailing community narrative regarding IOR yacht performance.