CBTF(Canting Ballast Twin Foil)

USA2, check out the page on the website below. you'll see a picture of a Melges 24 model that I designed and built(modified with approval of Melges and Reichel-Pugh) that is using an on-deck "Power Ballast System" coupled with a fixed keel. This is the boat that taught me the value of the hybrid setup because with a fixed keel the lead is just sitting there while the PBS does all the stability work.
With a hybrid ondeck system with a canting keel all the dead weight on the model is movable in the cause of going faster. This boat also taught me that scale hull designs -even way powered up- are no good for models: you want the lightest possible boat with the highest beam to length ratio possible with the most sail area possible. A beam to length ratio of 9 or 10 to one or better is fast as long as you have the righting moment.
For instance, a 50" canting keel hybrid ought to have a 50"wl with a max beam at the wl of 5.5" with 4.5" even better. Since it would use a hybrid system it should have a 4.5 pound bulb on a stiff ,thin 20" fin(6-7% t/c ratio) with around two pounds(incl. battery and variable) in the on-deck system. Wetted surface is less important on the fin than keeping it thin and stiff. Extra lateral resistance with CBTF or kFOIL- max 4/1 aspect ratio on the CBTF or kfoils...
But you should really consider an F100-it costs less and you'll help build a class...

See this page:
http://www.microsail.com/pbs.html

Note: PBS Systems or Melges no longer available for sale

[usa2]

after Im done this boat, I probably will get into the F-100 class. Right now I race soling 1 meters, but the F-100s seem quite a bit faster and more exciting to sail. What would be the upper wind limit for an F-100?

USA 2, sent you an e-mail...

[usa2]

got it

[D'ARTOIS]

Doug, what is the value of the distance between the center of the keeland the forward foil. Is a specific distance required, I believe it is, although it should not exceed........?

Mr. Dartois-the keel fin(strut) doesn't develop any lateral resistance and so it's position is not relative to the foils; it is placed where it needs to be to best support the ballast.
The foils are placed where they best reduce the wavemaking of the boat and the rig is placed relative to a point halfway between the two foils. The CE/ CLR reltionship is based on the foils being the same section and area ..

[amolitor]

I am looking at what latitude 38 CLAIMS is a picture of the capsized Skandia from the recent Sydney/Hobart. There's a lot of water around, but you're definitely looking at the underside of a boat. It sure looks like two foils one fore and one aft. and a rectangular opening where a keel used to be sticking out.

That would make it CBTF, no? Assuming the picture is captioned accurately, and that I am interpreting it correctly, of course.

This is in the Feb 2005 issue of Latitude 38, pp146-47. Could someone wiser than I with a copy take a look at it?

Skandia is definitely not CBTF; I asked CBTFco about it.
One usually tell tale way to recognize CBTF is that the foils are generally equidistant from the fin or close thereto.If the forward or aft foil is not in the "CBTF" position it is definitely not CBTF. There are numerous boats with daggerboards like Skandia; the daggerboard is generally significantly closer to the keel than is the rudder.
Anyway you could scan that picture?

[brian eiland]

courtesy of www.sailingscuttlebutt.com

LAUNCHING
We normally don't report on boat launchings, but there is a pretty
significant one happening on Monday, February 14 in Auckland, NZ. The boat
is the 100-foot Maximus, which is modestly described as the 'World's
fastest and most advanced supermaxi.' Designed by Greg Elliott and Clay
Oliver for New Zealand businessmen Charles Brown and Bill Buckle, boat's
featured include:
- Light displacement carbon fiber construction
- Rotating wing mast
- Retractable canting keel
- Maximum power to weight ratio
- 500 Square Meter upwind sail area
- 800 Square Meter downwind sail area

Previous commitments will prevent the curmudgeon from attending the
launching, but there is lots more information and photos on the GBS
Yachting website: www.supermaxi.co.nz/

[brian eiland]

Chris Ericksen:
As one who was in the hydraulics business for 15 years, the
stories of canting-keel problems occurring when an hydraulic ram or
cylinder is fully extended leads me to wonder why people don't use a
different hydraulic device to cant a keel: a rotary actuator. The kind I am
thinking of is a rack-and-pinion device wherein pistons attached to either
end of a rack rotates a pinion gear that would in turn be attached to the
axle of the keel. I am sure folks smarter than I have considered and
rejected this, but I wonder why this simple and robust device has not been
used heretofore.

Brian, I can't seem to find any mention of it; do you have reason to believe that this boat is CBTF?

[dougfrolich]

Amolitor,

CBTF refers to CantingBallastTwinFoil where the forward and aft foils rotate about a vertical axis, and is trade marked and or pat as such. CBTF does not refer to canting keel boats with daggerboard arrangements. The reason for all the extra foils is because when the canting ballast strut is canted it no longer develops effective lift to counter aerodynamic forces. ps looking at the same photo-glad I missed that adventure

[amolitor]

Yeah, I guess I am just looking at a pair of daggerboards. If they don't turn, then it's not CBTF? Even if they're on the centerline?

I would scan the photo except I stupidly forgot my copy at home. If nobody gets around to it, I'll try to remember tomorrow. It's a fairly depressing picture, but quite interesting. You don't get a good look at the bottoms of these boats all that often. Fortunately.

Amolitor, centerline daggerboards used for lateral resistance in canting keel boats sometimes cant (mini6.5) or rotate in addition to retracting but there are four ingredients missing: 1)the daggerboard and rudder are not located at the same place CBTF foils are ,2) they are not linked together such that the forward and aft foils rotate in opposite directions for the boat to turn and rotate in the SAME direction for "collective" steering, 3) they don't have the same area in each foil(usually),and 4) they haven't paid the CBTF royalty...
I'd like to see that pix if you or anyone can post it..

[nico]

Here it is.