Hydrofoils

Hydrofoils for SUP Geeks…

Every now and then there is a news flash on it, slowly but surely the word is getting out — some recon this is the next big thing, others skeptically look at it and shake their heads. 1st it was Laird Hamilton on a surfboard that made the surfing headlines and now more recently Kai Lenny on a SUP that had the social media networks buzzing….
 
 Hydrofoils….. or just Foils for short.
 
 But apart from the fact that it looks kinda weird floating above the water and it also looks like a mission to carry, I don’t really know much about it. When Ian from ZealSurf let it drop that he is planning to build a locally designed Hydrofoil SUP I went round asking some questions.
 
 *** 
 OH — Oliver Hobson — yachting enthusiast and the engineer behind the ZealSurf foil design.
 IW — Ian Wolmerans — water-man, entrepreneur & owner of Zeal Composites and Zeal Surf.
 *** 
 
 CTS: What is a hydrofoil stand up board?
 OH: A hydrofoil stand up board is the culmination of decades of aerodynamic and hydronamic specialists researching the subject along with material scientists improving their understanding of light, stiff materials such as carbon fibre.

The apex of this was the America’s Cup of 2013 which had 72ft boats weighing several tons skimming above the waves of San Francisco Bay at speeds in excess of 40 knots. This piqued the interest of the public at large and resulted in a huge uptake of hydrofoils on kiteboarding, windsurfing and sailing craft.
 
 The benefit of a hydrofoil is twofold; firstly it raises the rider and board above the water reducing the drag that has to be overcome to propel the board forward. This is the largest gain from the hydrofoil as it means that for example in a downwinder situation once the rider has caught the wave and the board has risen out of the water due to the lift produced by the foil, much the same way as a plane flies, the rider will be able to stay on the wave for a longer duration due to the reduced energy required from the wave to sustain the wave induced forward motion. Secondly, due to the way the foil is designed the foil can be ‘pumped’ by the rider to sustain the forward motion through lulls or flat spots between waves. In theory this could last for entire downwind runs, but hydrofoils are still in their infancy and all riders are still learning about their capabilities and limitations.
 
 Also, due to the better understanding of composite structures, lighter and stiffer foils have been able to be developed that allow takeoff to occur with less energy required and at a lower speed. This lower speed threshold is the breakthrough that allowed Sup’s to foil since the human providing the propulsion previously did not produce enough energy to overcome the extra weight that other materials would have.
 
 Ultimately a hydrofoil allows a rider to glide above the waves of the water with minimal effort to truly have a vastly different experience and could allow competitive riders to really enjoy the thrill of speed.
 
 CTS: How does the hydrofoil work?
 OH: The hydrofoil simply put, operates in the same way that a plane flies with wings. The only difference is that water is a denser fluid than air. This difference in density means that a wing operating in water will produce substantially more lift than the same wing produces in air. 
 
 In more detail this means that as the foil moves through the fluid it deflects the fluid in a partially downward direction which according the Newton’s third law will result in an reaction force in the upward direction. Also due to the shape of the foil and Bernoulli’s principle the fluid flowing of the upper surface has to travel a further direction the the fluid traversing the bottom surface of the foil. The result of this is a low pressure above the foil and a high pressure below the foil which then brings about a force in the upward direction i.e. lift.
 
 CTS: How easy / difficult will it be for the average SUP guy / girl to ride?
 OH: There will be a learning curve for even an experienced SUP rider since your balance above the foil has to be even more finely tuned than on a standard board. However, as with any sport, if the correct equipment is used the learning process can be accelerated. Ultimately with perseverance the average SUP rider will be able to experience foiling.
 
CTS: When can we expect the 1st Zeal Surf hydrofoils to be launched?

 IW: I was hoping to launch the whole foil project by the end of September, however the project has been delayed somewhat due to other priorities. The challenge of course is that I’m working for myself, so I’m building boards for customers and taking care of all the other things that takes priority in the business. Thus I’ve not really spend as much time on the foil as I would’ve liked. There also was a small issue in the initial build process and the prototype was binned, which is not all bad — it was a huge learning experience. Remember this has not been done with the same precision engineering anywhere else in South Africa, this is basically uncharted territory.
 
 This together with the fact that I’m off to the States in October means that I’m aiming to launch sometime in November.
 
 CTS: Do you think that there is a market for SUP Foils?
 IW: I don’t know. I’m building this foil for myself because I’m excited by the whole concept.. and if there is customers out there who want the boards I’ll be happy to build it for them. If there is a market I will continue to build, if not then I will have foil board that I can play with. I’ll attach it to it a downwind board and see what happens from there.

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