When paddling at speeds less than 10 km/h (2.8 m/s), the Flyak behaves just like a stable, conventional kayak.

When the speed increases to just under "take-off" speed, the front foil first lifts until it is about one chord length under the surface, and the Flyak is tilted about 1 degree backwards.

When the speed is about 25% higher than the"take-off" speed, the hull is lifted out of the water, and the Flyak is tilted about 1 degree forwards.

Top Speed can be more than 50% higher than "take-off" speed. At top speed, both foils are less than one chord length under the surface, and the Flyak is tilted about 3 degrees forwards.

There are no flaps or any other mechanisms that sense the surface to keep the Flyak level. About one chord length under the surface, the lifting ability of a hydrofoil decreases, so the Flyak is kept level by simply "leaning" the foils up against the surface. The foil winglets give added lift and directional stability.

The front foil is also a rudder. The front foil/rudder is controlled by the paddlers feet.

We recommend a paddle length of about 225 centimeters.

The graphs show the speed as a function of the kayakers total power output, when paddling a normal racing kayak (blue graph), and when paddling a Flyak (red graph). The total weight of kayaker, kayak and paddle is 90 kilograms.

The Kayak Graph (Blue)

When paddling a racing kayak, we know that approximately 25% of the power output is lost to turbulence around the paddle. From towing-test data (Jørgen Kvaleid, NTNU), we know that the speed power function of a kayak with 90 kg displacement is given by:

v = 0.57 × P^0.35

The Flyak Graph (Red)

When paddling a Flyak, we also have calculated 25% loss of energy due to turbulence around the paddle (This is a simplification: before "take-off", the energy loss is a little more than 25%, but after "take-off" the energy loss is just under 20%.).

It is easy to make a pair of foils (front foil and main foil) with a lift/drag coefficient of 20 (C_LD = 20). Of course, the lift/drag coefficient is dependent on many factors; for example the foil profile, the angle of attack, the aspect ratio and so on. A simplified graph, with constant C_LD = 20, gives a good illustration of the speed potential of a Flyak compared to a racing kayak:

v = 0.017 × P

To fully enjoy hydrofoil paddling, you will need flat water and a nice tail wind. The Flyak is all about speed, and the graphs show that the theoretical top speed of a Flyak is twice the speed of a kayak. At longer distances though, slow paddling in a normal racing kayak is more efficient than hydrofoil kayaking. Kayakers who are able to paddle 500 meters in 2 minutes or less, are fit enough to "fly".

The total weight of the kayaker and hull, together with the desired speed, dictate the area of the foil pair. Kayakers with a high level of fitness can use smaller foils, and thereby reach higher top speeds.

We have two ambitious goals: to break the top speed world record for human powered boats, and to go faster than the rowing eight over 2000 meters.

To break the top speed world record for human powered boats, we will use a "take-off" speed of about 20 km/h (5.56 m/s). At top speed the Flyak is tilted forwards, so that the angle of attack is reduced to about 1/3 of the angle of attack at "take-off".

To go faster than the rowing eight, we must carefully optimize the foils so that the lift/drag coefficient is 21 or higher.

Einar Rasmussen