Fenced V foil sail inflatable planB

Fenced V foil sail inflatable. Plan B.

Following some helpful comments from the forum conclude that the V foil proposal whilst relatively simple has probably too much drag to succeed. Looking at some of the successful dinghy's that have foiled Moth, Europe, Laser, Optimist, Waszp all utilise a single strut supported submerged T foil which logically would have less drag than a V foil. So to stand an improved chance of success plan B will be to increase complexity for better chance of success. Believe a simple parallel cambered plate (4% ?) from laminated ply with some GRP reinforcing at the slow speeds envisaged could work. Some of the craft above utilise a flap and wand to control height when foiling but not having any hull penetration it is more difficult. Proposal will be to form a central nacelle under the foil to house a linkage attached to a flap formed by cutting the foil at 30% and using some woven cloth glass grp for the hinge on top surface. The linkage attached to a bowden cable from a bike or similar such as a teleflex cable to a wand at the bow. Attaching a further bowden cable to a fulcrum led aft to enable additional control of the flap and enable manual trim. The additional control would allow overriding the wand to lower drag until say 5-7 knot reached and then deploy the flap for hopefully lift off and wand control. Area of foils around that of a similar weight radial Laser or Europe but increased a little aiming for lower 5-6 knot take off with 100kg main foil around 1.3m x 25cm and a rudder foil of 50kg lift. I wonder how does one calculate force to move the flap should treat as a small foil or percentage of lift ? Most flaps seem to be 30% however an article on the site with reference to sails suggests the shape of 1/6th of rear of foil controls 50% of lift which suggests a smaller flap perhaps. Further comments on proposal please.

 

I don't believe that anyone was arguing that the drag of the V foil arrangement in your first proposal was too high, rather the issue is that the drag of the boat itself prior to liftoff is likely to be high, making it hard to achieve the sort of boatspeed necessary to attain liftoff in the first place.

To address this proposal directly: learning to sail a T foil monohull while simultaneously trying to tune the setup is likely to be extremely difficult. I would suggest gaining considerable experience in a moth before building your own system. The general solution for trim control is to manually adjust the angle of attack of the rudder foil (either flaps or canting the entire rudder) not the main lifting foil.

 

Hi Thanks for your input. I have started to survey whats worked and find for example there are 3 lasers smallest sail is 4.7m2 I have I think arund 5.5m2 untested at present. Laser is 59kg the inflatable is 45kg plus my modifications which I think have added 10-15kg so similar. The Europe dinghy is also similar 60kg all up but 7m2 sail. The hull whilst an inflatable has what I would consider quite a nice hull shape given by the inflatable keel and planes readily one up with smll engine my guess 7-8 knots. Assuming my latest rig can stand a decent blow (mast from windsurfer not designed for cantelever support) which will add to some crude stay supports at position of windsuefer boom. New boom added at bottom of sail. The reason for initially going for V form foils was that I assume are mostly self regulating as far as trim and therefore simpler to fly but no practcal experience. I can see a V form has more wetted area and likely more drag especially considering actual length of foils rather than projected. I do have a start problem in that the centreboard is hung from the hull and pivots to raise so a T form will also need two vertical supports whilst those suppports could be foils if a V form used. If a T type foil is used it makes sence to me to regulate the main heavy lift foil rather than the rudder foil although can see some trim required at stern unless v form. Logigical route would be to tow craft behind cruiser and measuer drag . Sail in strong blow and measure speed. But I do have a good deal of time on my hands so with Covid lockdown and retired a wasted experiment would not be so disastrous and was looking for a low effort solution. So laminated ply thin plate form at low Rn I thought could work. Will do a few more sums does anyone know of similar e.g. heavier smaller sail area V form dinghys to look at ? Think Im past leaping about on a moth but would like a ride on an AC75 if was offer