International Journal of Small Craft Technology


INTERACTIONS BETWEEN YACHT-CREW SYSTEMS AND RACING SCENARIOS COMBINING BEHAVIOURAL MODELS WITH VPPS


M Scarponi and P Conti, University of Perugia, Italy R A Shenoi and S R Turnock, University of Southampton, UK SUMMARY


Considerable progress has been made in the development of Velocity Prediction Programs (VPPs) suitable for analysis of racing yacht performance. In addition, investigations on yacht dynamics (i.e. optimal tacking procedure) are now available. While these tools will no doubt be further refined and computations speeded up, there is also a need to assess the performance of the yacht’s helmsman and crew.


The scope of the present study is the prediction of the performances of a yacht-crew system as a whole, by deriving numerical models for human behaviour alongside with those referred to the physics of yacht motion. The latter issue, the mechanical side of the problem, is analysed by solving yacht equations of motions in the time domain; crew inputs in terms of yacht steering and sail trim are considered. The yacht-crew system can sail a racecourse in an arbitrary wind pattern, according to strategic rules and given decision making schemata.


NOMENCLATURE awa


awaref apparent wind angle reference apparent wind angle


twa true wind angle DMG distance made good


1. INTRODUCTION


The use of Velocity Prediction Programmes, (VPP) to assess yacht performances can be regarded as a well- established


technique in yacht design. Considerable


improvements were actually carried out in the last decades, in order to achieve a closer modelling of hydrodynamics and aerodynamics of sailing yachts [1]. As a result, designers can now obtain valuable information on the straight-line, equilibrium state of a yacht for each point of sail and wind speed. Screening among a fleet of design candidates is also possible through VPPs: a ‘test fleet’ can be generated, usually by applying systematic variations to a ‘base boat’, and the minimum time required to complete a set of racing legs can be predicted. VPPs have also


been used in


conjunction with weather databases, in order to predict the outcome of races [2]: these are usually identified as Race Modelling Programs (RMPs). It is widely felt that further additions to the traditional models for yacht performance prediction are necessary: as an example, in Keuning et al. [3] it is pointed out that aspects of yacht dynamics (namely, the tacking ability) should also be modelled for handicapping purposes.


One of the distinctive features of modern yachting is clearly one-design racing:


the attention of either


yachtsmen, designers, sponsors and media is actually switching to contexts where the skill of crews and the ability to make the right decisions at the right time are keys to winning races. In the Authors’ opinion, any


2.1 BACKGROUND ON VPPS


The goal of VPPs consists in solving iteratively the equilibrium equations of a sailing yacht subject to hydrodynamic loads (hull


and appendages) and


aerodynamic loads (sail plan). The steady state surge speed of the yacht can therefore be calculated for a range of wind speeds, points of sail and sail inventories, which then gives designers an insight into the overall quality of their yacht design. The reliability of VPP predictions is closely related to the quality of experimental and numerical


data models are based.


To bear the costs of a close modelling of a sailing yacht, with the purpose of getting accurate VPP predictions, is still far from being an easy task. In fact, access to facilities such as a suitably-sized towing tank and a wind tunnel is required, in


order to investigate the


hydrodynamic behaviour of appended hulls and to build up the aerodynamic model. A numerical approach in terms of Computational Fluid Dynamics can also be regarded as a valuable


source of information, but


traditional testing can hardly be avoided, since numerical methods can provide just partial responses to designers.


upon which the aero-hydrodynamic


improved approach to performance prediction should therefore aim at taking two factors into account: the racing


hardware, the boat, and the software (or


wetware!), the sailors. Regrettably, little or no published attention has been paid to the latter issue so far. This seems to be paradoxical, since sailing is a discipline so rich in


predicting


uncertainty that gambling, taking chances, future scenarios,


assessing


decisions always come heavily into play. 2.


outcomes of YACHT PERFORMANCE PREDICTION


©2008: Royal Institution of Naval Architects


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