This doesn't have to do with surfing, but it sure provokes thought. Check out: www.aquaskipper.com. What do you all think? Seem like there is pretty easy glide. What would happen with wave energy behind the foils?
The AquaSkipper (formerly Trampofoil) is a very cleverly designed, human-powered, hydrofoil-based, recreational watercraft optimized for use on a flat, or nearly flat, sea surface. Key elements of the design are a very low weight (~26 lbs), a very high aspect ratio fully submerged main hydrofoil, and a unique, propulsion system in which the the rider pumps up and down with his legs, thus causing the main foil to flex and produce forward thrust as well as the lift necessary to support the rider and craft. A small forward (canard) foil and strut combination (“Shutt Strut”) control the flight height and direction.
(See upper-right image at: http://www.aquaskipper.com )
A major limitation of this design is that it can’t do “water starts”. Instead, the rider must launch the craft (and himself) by pushing off from a fixed (or semi-fixed) object such as a pier, a dock, a rock, a raft, a boat, etc.), then leap onto the craft and immediately begin energetically pumping with his legs. Once the rider has successfully launched the craft, he must pump continuously and with sufficient energy so that the craft continues to “fly”. That means that the surfer must continue to expend energy while waiting for a suitable wave to ride. If he cannot maintain this level of energy the craft will settle into the water and the rider must swim the craft back to a suitable launching site (or into the beach if he is done).
It remains to be seen if it is possible to do a water start if the wave face is very steep. But with virtually no mobility to position (swim) himself relative to the wave face, that doesn’t sound like a desirable alternative–even if possible.
Unfortunately, with these limitations and requirements, it would seem that the most viable solution is to be towed up to flying speed and then maneuver to catch a wave, or be towed into the wave the surfer selects to ride.
As long as the slope of the face of the wave is small at the position of the rider on the wave, or the rider is going “straight off”, the board should handle more or less like it does on flat water. However if the rider chooses to go across the face of the wave (as well as toward shore) the stability and the rider’s ability to control the board become problematic. In particular, the lack of symmetry in the flow-generated forces on the board can be expected to generate a rolling motion toward the “shore side” of the craft. In general, the severity of this type of problem will increase with increasing speed, with increasing steepness of the wave face, and with the design of the craft (especially with regard to the span of the main foil). This effect may challenge the rider’s ability to compensate and is likely to result in a wipe-out. Since a high aspect ratio main foil is used in the AquaSkipper, it would seem likely that roll control this could be a significant problem–especially in hollow waves with wave heights (/curvatures) comparable to the span of the main foil.
When the craft is moving across flat water, the functions of the forward (canard) foil and associated strut are two-fold: (1) maintain the “flight height” of the craft and (2) allow the rider to control yaw (direction). With proper design, these two functions can be made independent of each other when traveling on a flat sea surface (or going straight off on the face of a wave). Pitch is automatically controlled while yaw is rider controlled. But if the rider is moving across the face of the wave the effects from the two systems can become intwined (i.e. the foil begins to influence direction while the strut begins to control pitch). The result is a complex response. This “mixing” also makes it increasingly difficult for the rider to anticipate consequencs and maintain control of the craft.
My overall assessment: Could be fun to play with in suitable conditions, but likely to be marginal in anything but very modest surf (unless you’d like to explore how it works for you).
A few performance specs from http://www.trampofoil.com
The Trampofoil is a Human-Powered hydrofoil with flapping wing
propulsion. The Trampofoil® gets its supporting and propelling
force completly from the hydrodynamic lift on its hydrofoils. The athlete
jumps with both feet together and pushes the hydrofoil alternately up and
down. The vehicle is normaly started and landed on a jetty and it is not
possible to start from the water with the present configuration. The speed
interval is from 2.5 to 6 m/s (5-12 knots). The current distance record is
11.5 km (A. Sahlin 1997).