The development of a reversible and finitely variable camber windsurf fin.

Abstract

An investigation was undertaken to identify and develop a practical method for improving the lift to drag ratio (LID) of the contemporary windsurf fin. It was established that the contemporary windsurf fin is at an advanced stage of evolution and that a fundamental reworking of the design is required to attain significant L/D gains. In particular the symmetrically foiled cross-section (required for equal performance on each sailing tack) limits the performance potential of the device. The benefits of using camber in the design of lifting sections for high lift and low drag are well known. Traditional variable camber lifting surfaces utilise leading and trailing edge flap technologies to vary the geometry (camber) of the cross-section. However, this method for generating variable camber is not considered to be suitable or practical for the windsurf fin, primarily due to the increases in drag associated with conventional flaps. An alternative approach for developing a variable camber windsurf fin is therefore considered. It is proposed to use hydroelastic tailoring techniques to realise a reversible and finitely variable camber cross section for the fins used in the sport of windsurfing. The camber in the cross-section is invoked by the pressure differential acting on the two surfaces of the fin when it is at an incidence angle to the freestream. The magnitude of the camber is adaptive and responds passively by design, material usage and sailor input. As part of the preliminary investigation a computer based analysis tool was developed to perform the two dimensional investigation into the coupling effect between the fluid flow and the hydroelastically tailored cross section. Based on the outcome of this work a prototype windsurf fin employing a hydroelastic cross section was fabricated and tested. Results from this preliminary investigation establish the potential for using a hydroelastically tailored cross-section to significantly increase the L/D performance of a windsurf fin of nominal surface area (when compared with contemporary designs).