University of Twente Student Theses


Effects of rig tension on sailing yacht performance : internship report

Bergsma, Friso (2012) Effects of rig tension on sailing yacht performance : internship report.

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Abstract:In yacht racing the aim is always to go faster. In every sailing competition yachtsmen try to make their boat go as fast as possible. Even in the smallest details efforts are made to pursue an increase in performance. The Stewart 34 is no exception to this rule. This yacht is designed by Bob Stewart in 1958 and is raced very competitively in Auckland. It is noticed that many of the top boats have very slack cap shrouds causing a big sideways deflection of the mast(top). The believe is that the increase in performance is cause by these slack cap shrouds. The research presented in this report was conducted to find out if the performance actually increases due to slack cap shrouds, and what causes this increase in performance. Full scale tests were performed on the Stewart 34 ‘Pride’. Aerodynamic forces were determined and compared for different shroud settings. Using VSPARS and discrete pressure measurements the shape and pressure of both sails of the Stewart 34 were measured. These were extrapolated to obtain the full shape of the sail and the full pressure distribution. With this data the force components could be determined. Forces were determined for systematically varied cap shroud settings. These forces were normalized by correcting them for wind speed and apparent wind angle. A correction is applied to account for the variation in performance due to variation in apparent wind angle. This leads to performance indicators named corrected driving force made good (CF_(x,MG,η)) and corrected heel moment made good (CM_(x,MG,η)). It is found that: The value of (CF_(x,MG,η))/(CM_(x,MG,η) ) maximizes for most combinations of tack and heading at a rig setting between medium and slack. And exception is shown in the measurements on port tack while heading for maximum VMG. The fall off of the mast top clearly increases with slacker cap shrouds. This is shown for all combinations of tack and heading. The gap width has a minimum for the medium shroud setting. As expected the gap width increases with increasing slackness of the shrouds. However the gap width also increases when the cap shrouds are set to tight. For four out of six cases it is shown that the corrected driving force made good increases with increasing gap width. This indicates that there might be an increase in performance associated with an increase in gap width.
Item Type:Internship Report (Master)
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
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