Hydrofoil

During the summerseason of 2002 I've built a hydrofoil (Dutch: 'draagvleugelboot'), with help of my brothers Pieter and Thomas. A hydrofoil is a boat that lifts itself out of the water when it has gained sufficient speed. The lift is generated by wings (hydrofoils) mounted below the hull. In the selfmade design here described we used a surfboard and an outboard engine of 5hp. This engine seems to have insufficient speed on its propeller, and as a result the board only just manages to escape the water. This is understandable considering that these engines/propellers are made for lower speeds, and heavier loads. We have thought of buying a faster engine for the board, but small engines for high speeds are hard to come by.

On this page some photos of the hydrofoil. Click the thumbnails to view the photos.

The whole thing out of the water. The back wing has a settable fixed angle, while the front wing has a mechanism to adjust its angle to the depth in the water, so that it stays at a constant depth.

This is me on the hydrofoil. It seems I'm enjoying it :) You can see that the ski at the front is high above the water, which it should not. It should ski on the water to adjust the angle of the front wing. As a result the board often rises too far above the water, looses forward thrust, dives down and then regains speed. It's like riding over small hills with a bicycle. So there's work to be done.

Thomas on the hydrofoil.

In spring 2003 I did some modifications to prevent the 'hill cycling' behaviour, and also some changes to make it more stream-lined. The front and back wings now look like this. The large back wing is now adjustable "from the cockpit", so we can trim it. We've also added a throttle lever, so you don't need to adjust it on the engine.

In 2005 I made some modifications to the frame, making it lighter. I also want to mount a smaller, lighter fuel tank. And in 2006 I've adjusted the hole in the surfboard for a bigger engine (9.5hp) :) It now lifts above the water without any problems and we think it goes between 20 and 25 km/h.

Movie here (5MB, moving jpeg)
Again with Thomas at the helm. Notice how small the "bow" wave is it generates. It also cuts through waves as if it has air suspension, unlike planing speedboats.