A Photo & Discussion Forum for Wharram Design Enthusiasts
After more then ten years of sailing my Tiki 26 Freyia, I decided I needed to do something to get her a better speed when surfing or sailing downwind in stronger winds. The biggest problems we had was that over a certain speed like 10-12 knots, Freyia has the tendency to sink her sterns so deep that first the outboard leg and then the whole cockpit would "touch down" and so bringing the speed down to 6-8 knots. As a friend of mine had a bunch of helicopter wings and rotors laying around I persuaded him to give me some parts of an heli-heck rotor blade made out of solid carbon and glass fiber at the front and filled with closed cell foam in the middle part.
Last June I found time to add these wings to the stern of each hull, just in front of the rudder, and during my sailing trip, could experiment with the adjustments of angle and get some nice results.
After adding these winglets Freyia is now sitting much higher with her sterns when starting to surf down waves of 3 feet or higher. When getting over 25 knots of wind we seldom touch down anymore, but could have a couple of days when we would run at 9-11 nm in one hour. So these little foils bring the v-hull the much needed gliding surface aft. Each of the four foils is about 12 inches (25 cm) long and has a profile very similiar to a NACA 10 one. I calculated that each hull should get a lift of about 20-30 kg at about 10 knots when the attacking angle would be about 10°. I have made the angle of attack a bit adjustable, (but I need to go swimming for doing so) and found out that they must be nearly horizontal when the boat is not moving. The angle comes from the stern sinking deeper when speed gets up. Giving them bigger angles was not helping but adding more drag and slowing the boat. When running on the engine full throttle and horizontal adjustment I did not loose any measurable speed loss. Only when sailing at 2-3 Beaufort Freyia might have lost a 1/4 of knot, compared to no foils.
So over all I am very pleased with this addition, one additional bonus being to be able to climb aboard Freyia easily when boarding after a swim, instead of putting down the ladder.
I will add some pictures of my construction, please feel free to ask any questions..
Brilliant ! Now that you have worked out the angle have you fixed them in permanently ?
Those bolts and angle brackets would be draggy as all get out !
A couple of points.
I would angle the foils aft a bit so they don't collect weed.
I would reinforce the skeg with some extra glass as the lift force is taken by them.
Beach cats don't have the leading edge skeg so that is why the foils go on the rudder, although the extra depth on a beach cat rudder would give greater leverage, not really applicable to the Wharram set up.
Have a look at this Tane rudder set up here.