Trans RINA, Vol 1521, Part B1, Intl J Small Craft Tech, 2010 Jan-Jun


whose definitions are reported in [19], and is also far from being related only to the edge separation at the shear line of the deck [20]. Wind-tunnel force measurements have been performed by [21], [22] and [23] on upwind sails to investigate the heel effect. These authors reported a reduction of the drive and side forces with heel. More recently, forces have been measured in downwind conditions [24] and a force increase at low heel angles


was reported. The present pressure


measurements show that the drive force increase at low heel angles is correlated with a larger suction peak, whilst the drive force decrease at large heel angles is correlated with an earlier trailing edge separation.


Figure 5: Cp at 55° AWA versus the curve length for 0°, 10° and 20° heel, measured at different fractions of the mitre (from the top to the bottom): ⅞, ¾, ½, ¼ and ⅛, respectively.


4.3 EFFECT OF SAIL SHAPE


Figure 4: Cp versus the curve length for 40°, 55° and 70° AWA, measured at the different fractions of the mitre (from the top to the bottom): ⅞, ¾, ½, ¼, ⅛, respectively.


The 3 sails had different shapes and were designed for different purposes. As noted above, the A1 is designed to sail at low AWAs and the A3 is designed for large AWAs. The A2 is an all purpose sail which can be sailed at medium AWAs with good performance but has a wider AWA range where the performance is still acceptable even if not optimum. The force trends show that the A1 performs better than the other sails at low AWAs and that the drive force does not decrease with


B-46


©2010: The Royal Institution of Naval Architects


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