Foiler Design II and Construction I

This topic was accidently deleted today (see "Problems, Solutions).
I will add some of the information that was lost and suggest that those interested first read Foiler Design below-a locked topic.
Foilers for rc sailing are relatively new and offer dramatic benefits in stability and speed. When compared to normal rc multihulls perhaps the most important benefit of the type foiler dscribed here is that of automatic,all weather stability control: the foils with their wands sense and maintain altitude but also sense roll and prevent it by using the power generated by the hydrofoils themselves. The basic system was devised by Dr. Sam Bradfield(and before him Philip Hansford) and is incorporated on his Rave and Scat foilers. An rc version has been built called the F3 using this system. The beauty for models in addition to breathtaking speed is that the system vitually eliminates capsize or pitchpole as the wind gets stronger-no conventional multihull can offer this kind of stability.
This information is posted for the experienced boatbuilder whether business or not: the idea is to get as many foilers sailing as possible. It is also posted for the begining multihull sailor of which this type of boat is absolutely ideal; I’ve had years of experience sailing conventional rc multihulls and years of sailing a foiler and the foiler is far easier to master in strong winds than any other type of multihull: a begining multihull sailor can expect high speed, quick turns right off the bat in strong winds
with no capsize or pitchpole.

The information here and below in Foiler Design can be applied to multiONE multihulls , F48/mini40’s and to two meter multi’s. Trying to build a foiler from scratch or even a kit requires expert modelling skills and a basic understanding of sailboat design.The information below is for a Formula 48 foiler but can be varied to suit other sizes of multi.

  1. position of the main foil is described below as at the point where it carries 80% of the weight of the boat, measured at the quarter chord point.In doing your design you need to locate this point first.The location of the vertical fin that supports the hydrofoil is done by first locating the pushrod control tube in the vertical fin: it should be aft as far as possible but big enough that the push rod can move fore and aft as the flap moves + or - 25 degrees. The pushrod should intersect the flap at the halfway point fore and aft and that gives you the vertical fin location. To set rig location you can align the geo CE with the quarter to mid chord point of the vertical fin-no lead at all.
  2. Use a main hull with a CB at 53% and a prismatic at static at around the same(say 55 or even less)-the main hull should be optimised for light air. The beam to length of the main hull should be 13-14/1 . Main hull displacement should not have to exceed 5.5lbs.(2.5kg).Minimum achievable appears to be 3.5lb.s(1.5kg) Shoot for: 4.4lb.(2kg)
  3. Ama total buoyancy should be between 5lb.s(2.27kg) and 7lb.s ; smaller is better . Keep the beam to length as high as possible-around 18/1 is ideal. Ama CB should be an inch or two(25-50mm) AHEAD of the CB of the main hull.Lenth of the ama doesn’t need to be any more than 36"( just under one meter)
  4. the best design to use here is a retractable foiler because you will not need to install ANY trunks inside the hulls and because the retractable system is easy to adjust that way.
    IMPORTANT: you can choose to build a retractable or fixed foiler; Both will foil in 5-6mph of wind. The retractable foiler has NOT been tested ; the fixed version has. Both use the same foil system and the retractable system is quite simple. The first prototype using the retractable system will be sailing before too long.I recommend that design because I believe it will work perfectly: you can use the basic retractable mounts for a fixed set up and convert to retractable later very easily!

In either case a torsionally reinforced carbon cross arm is required: .062"(1.57mm or so)WALL by 1"(25m)ID.
A supplier in the states is McLean Quality Composites.
5) details of the wand system can be supplied as sketches-just contact me; same with the retractable system.

More Later…

edt:add minimum achievable weight
Doug Lord
–High Technology Sailing/Racing