FOILTWISTER

The idea of travelling at a low cost with hydrofoils is old. Already in the fifties hydrofoil based boats were used for commercial purposes for quick trips. The drawbacks were unfortunately many - foils stuck out from the sides and the boats were difficult to dock at a pier. It also became very bumby when the boats went through high waves. Another drawback has been the advanced control system as needed on older hydrofoils.

Elektrofoil now with our solution foiltwisterlogo solved all this with an innovative and stable solution.


The most effective type of hydrofoils is when the lifting wing is fully submerged below the water surface, and is connected to the hull via the streamlined struts passing through the water. The hydrodynamic force on these struts is small compared with the foil's lift.

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A problem with this configuration is that the vessel becomes unstable sideways, as the craft center of gravity lies above the hydrofoil and struts.
This instability has previously been handled with active steering, much like on a bike, or with an electronic computerized control system linked to the ailerons on the hydrofoil.

Our patented solution with twisting foils shown in an animated sequence above.

 
Foiltwister is a new way to stabilize fully submerged hydrofoils. The struts is freely pivotable sidways. If hydrofoil starts flogging, it moves to the side of the heels, causing the struts to twist. The struts rotation axes are oriented so that one strut is rotated forward and the other backward when turned sideways. This forces the blade to skew itself, giving an aileron effect which rectifies the boat.

The slope of the axes of rotation for the struts determines the gain in the lateral stabilization. Too little gain may lead to large lateral movements when the system compensates for the waves and uneven load, and in the worst case course instability. For high gain, on the other hand, require unnecessarily large lateral force to the struts to shear the foil.
Through simulation and extensive field testing, we verified the gain that are best suited.

Lateral stabilization in this version has worked without problems from the first attempted several years ago.

Our solution is completely without either any hydraulics or electronics and based solely our pure mechanical rotating shafts, struts and a twisted hydrofoil - a solution that is simple yet brilliant.

Height regulation has required more development work. The requirements for the system are both to keep a stable altitude and the system to be robust. Because of that we have avoided sensitive rudder flaps on the rear end of the hydrofoil. We have tested the height control both on the forward and end foil with different designs and reinforcements.
The solution proved to work best is to turn the entire front hydrofoil. To avoid large control forces when the hydrofoil is moving forward / backward rotation is a roller body so that the pivot point always is moved with the foil.

To verify the technology we have over several years built up a number of test platforms from a small radio controlled model and then various full size boats. Currently our newest concept boat is a 5.8 meter aluminum boat specially designed for our hydrofoil solution

Additional information