I’ve experimented with canting keels for years; the latest boat I used one on was the aeroSKIFF a 42" model. The keel canted 52 degrees and went from center to full out in about 1 second.(the new F100 will use the exact same system) Because the boat was designed to use hydrofoils it had a daggerboard just ahead of the canting keel since all canting keel boats need some form of extra lateral resistance in moderate to heavy air when the cant angle of the keel reduces its effectiveness. In the course of developing the aeroSKIFF an opportunity presented itself to secure the world wide rights to CBTF Canting Ballast Twin Foil technology . And to secure the services of Graham Bantock to design such a boat PROVIDED the computer analysis using his proprietary VPP(Velocity Prediction Program) showed that it would be the fastest one meter monohull(not on foils!). So I put the aeroSKIFF aside with the concurence of the customers that had ordered that boat in favor of going whole hog in the new CBTF F100 direction. From day one the design was to be within the parameters of the new Formula 100 Class(the only development monohull class to allow movable ballast) and the design goal was first and foremost to produce the fastest one meter monohull.
In the analysis done by Graham(see the three reports published on this site under the articles section–click on HOME and scroll down) it was determined ,to a high degree of accuracy, that a fixed keel F100 would beat an IOM in all conditions and that a canting keel F100 would beat a fixed keel F100 in ALL conditions. The downside was that “normal” CBTF- that is twin rudders: one forward, the other aft -could not be used in all those same conditions.
(UPDATE: see “CBTF RULES!!!” under New Classes and watch for a Canting Ballast Twin Foil thread in this section. The final Bantock design is in and with a number of significant refinements he has shown that a CBTF F100 WOULD be superior to the fixed keel version of an F100 IN EVERY CONDITION ; the fixed keel F100 is already superior to an IOM by large margins.That Graham was able to reduce displacement, wetted surace and drag so much from the generic CBTF boat mentioned in report two and three is a GREAT testament to his design ability and to the application of science to model yacht design.
This post presents some alternatives to CBTF that may also be fast but likely no where near as fast as CBTF 8/14/03)
Either the forward rudder would have to retract upwind in under 4 or so mph of wind and downwind in 6mph and under or a retractable daggerboard would have to be used to reduce wetted surface.
The fact is that a canting keel equipped one meter was shown in Grahams testing to be FAR SUPERIOR to the other two one meter monohulls for which he had or developed data:the IOM and the Formula 100 fixed keel.
Also clear was that a new version of a CBTF boat with a retractable forward rudder would be the fastest of all. Unfortunately, as of now we haven’t come up with a good solution to make the retractable rudder practical.So utilizing a daggerboard seems like the way to go at present. I discovered that using a daggerboard on the model would require a different set up than is frequently used on fullsize boats where the canting keel strut is not usually designed to provide any lateral resistance. Because of Reynolds number considerations the model canting keel strut is easily adaptable to providing lift(lateral resistance) at low speeds because its thinness provides a longer chord than would be used on a full size boat. The fact that thin foils (6-7% thickness/chord ratio) are better for model foils mandates a longer chord that coincidently can be used to provide lateral resistence. On big boats ,especialy CBTF boats, the canting keel “strut” is just that -not a fin at all and if sailed in such a way that it was forced to develop lift would result in great drag. Thats why CBTF boats have collective steering that allows leeway to be eliminated allowing the strut to have streamlined flow and produce no induced drag.On a canting keel boat-full size or model the ability to have a “gybing” daggerboard can accomplish close to the same thing as collective steering on a CBTF boat. But back to the different setup: most fullsize canting keel boats that use a daggerboard have the daggerboard in front of the canting keel strut since the strut is NOT developing lift.
On the model since the keel fin IS developing lift and the daggerboard is only used upwind in moderate to heavy air the solution I discovered is to put the daggerboard BEHIND the canting keel. That way the Center of Lateral Resistance is forward in light air and as the wind picks up the daggerboard is lowered moving the center aft which matches the movement of the rig Center of Effort.
This is a great improvement in controlling the balance of a canting keel boat throughout the wind range.
I think well designed canting keel boats have great potential in the future and they definitely bring more speed and more challenge to rc sailboat racing. Oh yeah: and MORE FUN!
Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing