DIETRICH ‘RICK’ HANKE, MAUI ULTRA FINS
Rick Hanke, founder and fin designer of Maui Ultra Fins, is renowned for his standards in fin design, combining his passion for windsurfing with his professional background in aero and hydrodynamics ( study of aeronautics at the University of Braunschweig, Germany and his long time scientific work on flight mechanics and flight simulation with the German Aerospace Agency, DLR). Rick’s fin design and development work follows a scientific approach by using computer assisted foil design (Computational Fluid Dynamics, CFD) and CAD design (Computer Aided Design) for the final 3-dimensional fin. With a successful range of fins across all disciplines, we asked Rick for his specific thoughts on slalom fin designs.
Rick Hanke – “Slalom fins have a very specialised design brief that includes:
• Wide wind range from about 9 knots to force 9 and beyond.
• Wide range of angles on course and speeds are needed.
• Any slalom fin – responsible for directional stability – has to compensate the varying leeward-forces of the sail with a minimum of drag.
• Depending on course angle and sail trim, the needed forces vary a lot. That means that the fin, defined by lift over drag at different angles of attack, has to cover the whole polar range.
The consequence for slalom fin design is one profile has to be developed that works in high angles of attack without spin-outs and that has a low drag at low angles of attack at high speeds. The matching profiles / designs have a relative thickness between 9 and 10 per cent, high aspect ratio for minimum resistance / drag and must be stiff enough not to break, so to withstand the side forces.
The size needs to be defined by fin area as it counterbalances the sail forces – therefore fin lengths can be misleading (our Slalom-Race fins are wider and have more area than the Slalom / Slalom-Pro so can be used about 2-4 cm shorter).
The fin area needed mainly depends on the weight of the sailor, the board size / width and sail size.
Slalom fins need to have a certain degree of flexibility (flex) to create a vertical force (lift) at the tail of the board – to get a flatter water line and reduce drag – and to keep control at high speeds.
Slalom fins have to match the rider’s requirements, more so than with freeride, wave or freestyle fins and different designs are needed.
Maui Ultra Fins therefore has designed:
• Standard slalom fins with a moderate thickness and the thickest point further forward for early planing.
• Wider high performance slalom fins like the ‘Slalom-Race’ in G-10 and carbon that plane earlier and facilitate “easy” high speeds.
• Narrower / even flatter and therefore faster designs with the ‘Slalom-Pro’ (also G-10 and carbon) with even better control in heavy chop / high winds.
Too much / little lift in a fin can be completely or partly be compensated with sail and board trim to create more lift. I carefully calculate profiles and outlines using fluid dynamics calculation before first prototypes are made. Those prototypes are then validated by experienced slalom sailors and improved. The focus here is often on the flex behaviour.
According to our experience, fins up to a length of 36 / 38 cm are more often made of G-10. Beyond that size, most riders prefer carbon slalom fins. Those benefit from freedom in design as the bend / flex can be defined through the different layers and positioning of fibres – independent of the profile. Carbon is very light and stiff so that these fins can get a narrow / thin profile without breaking.
Maui Ultra Fins decided to produce the carbon fins at a very experienced German producer of carbon composite parts. THM in northern Germany manufactures our fin in a steel form in an RTM procedure (RTM=Resin Transfer Mould). This production process allows for the highest precision and same quality for all fins (weight, bend curve etc.). A special high-end resin is heated and vacuumed into the steel form that already contains the fibres that are cut and laid up. As the resin is not brushed by hand upon the fibre, there is absolutely no variation in quality.
These fins are absolutely high-end due to the inner construction and finish. They are also the lightest on the market. Maui Ultra Fins offers three different carbon fin types. On top of the above mentioned
Slalom-Pro and Slalom-Race-Carbon, we offer a weed version, the Slalom-Race-Carbon-Weed with a rake of 45 degrees.”