CBTF(Canting Ballast Twin Foil)

[Paul B]

I just returned from New Zealand. While I was there I saw the new R/P designed MaxZ86 Pyewacket doing some testing at the dock.

This is a CBTF design. You can see the upper bearing for the forward foil on the foredeck. I don't know if this is full cant or not, but it is as far as I saw them go.

I believe they will be doing the Sydney-Hobart race in a few weeks.

Paul, thanks for the picture!!. I'm not 100% sure but I think in the Sydney -Hobart they may be limited to a static cant that only heels the boat 10° ; she appears to be substantially more than that in the picture-probably just testing. I know that Maiden Hong Kong also using CBTF(despite theSailing World article) will statically heel 37° with her keel at max cant.
Is there a url you know of with more pix? Thanks again...

[nroose]

Perhaps you all have seen them, but there are some other pictures of Pyewacket at http://www.outsideimages.co.nz/index.html.

[Wardi]

At the risk of raising what may seem a stupid question,....why is there such a focus on CBTF at present?

Surely there would be far less resistance if the moveable ballast were on deck, instead of under water!

Also, while these boats may be actually faster, surely they still have to be competitive on handicap.

Is this current fad purely a result of the current rules which do not allow moveable deck ballast other than water, and a handicap system which has not caught up with the benefits of this new configuration.

I really do not understand how a boat with moveable ballast can be effectively raced against one which does not.
We do not expect to effectively race dinghies, cats or sailboards against yachts and so we have separate divisions.
Surely the same should apply to the various categories of yacht eg: Keel ballasted, Crew ballasted, Water ballasted, CBTF etc

Ian, I sure don't think CBTF is a fad it has shown itself to be very fast. Putting the ballast on deck is worth experimenting with and I have done that with models: a boat so equipped is almost unsailable without a certain proportion of the ballast still in the fin or buoyancy pods accompanying the ballast to prevent capsize.The buoyancy pods change the definition of the boat from mono to multi in some peoples minds. In models things are speeded up a lot so there is room for experiment on big boats but there is little chance of such a system being adopted for prouction given the great resistance in some quarters to new technology in the first place.
But the canting keel allows around a 50% reduction in ballast for the same SA as a "normal" mono so represents good progress.
But the equally important aspect of CBTF is the ability to use collective steering to eliminate leeway upwind. Turning both foils a few degrees to weather alows the hull to go straight thru the water and allows the canting strut to uses a shorter ,thicker section than would be possible if it was developing lateral resistance.
CBTF is not the only canting ballast technology but it is probably the fastest especially upwind....

[SailDesign]

Doug, I'll take exception to your last statement, but only a little ;-)
I think the canting keel/twin dagger board set-up is probably just as fast upwind. Not faster, but as fast. The same lift is developed by the boards as by the CBTF foils, probably with similar aspect ratios, hence producing similar drag penalties.
It would be a close thing.

Ian, you may be too hung up on ratings. There are a great many people who are just not interested in the whole ratings game any more, and just want to go fast. In the Open Class world, you can take your choice of ballasting systems, no holds barred (or very few) so the fastest technology is what wins. It's a great game.

Steve

Steve, exception noted but CBTF allows the angle of incidence of the twin foils to be varied as necessary depending on conditions . According to CBTFco, the placement of the twin foils adds an advantage not achieved by twin asy boards and that is a reduction in wavemaking resistance.

[SailDesign]

LOL!! - If you can explain it in simple words, I'll believe it, but otherwise......
If you want to be picky (I'm jesting here, mostly) then the asymm boards help to equalise the pressure on the high-pressure side of the boat as well, which reduces wave-makng resistance by, what?, a whoel0.01% or so.

Hey Steve-glad I could provide you with a good laugh! Seahorse magazine provided a simple clear explanation of this regarding CBTF boats three or four issues ago(or more back)--it's apparently one of the unique and real advantages of CBTF. If I find it in a quick search I'll post it here; when you're thru laughing and if you want to hear it from the horses mouth I'd invest in the time to send an e-mail to Bill or Bruce at CBTFco(info@cbtfco.com)
-who knows you might learn something.....Merry Christmas and Happy New Year etc!

[BrettM]

Sorry to say it, but I happen to agree a little with what wardi is saying. CBTF whilst all very interestingin the technical sense, it amuses me with the fact that all this money is being spent on boats that do seem to comply with the spirit of the rules. (ie amount of cant/heel available etc etc). If one really wanted to go fast and ignore the rules a multi seems a good choice. Take the example of the guy who buys a 300k mono who is beatern around the buoys by a guy in a 100k multi who in turn is beaten by two guys who have pooled 5k into a second hand off the beach cat.
(I'm goin to get jumped on here)


Have a merry Christmas all....

I personally would prefer a multi or mono foiler for my inshore sailing because I love speed under sail BUT there are different degrees of fast.
If you look at design progression in mono's you cannot realistically deny that CBTF is a giant step forward-not just because of the light displacement made possible by the canting keel but also because of collective steering and reduced wavemaking.
I think down the line we'll see hydrofoils on mono's with canting keels and other developments within monos that are significant. Right now with the exception of Mari Cha and some boats specifically configured fo the Sydney -Hobart the big CBTF boats like Genuine Risk, the two maxZ86's,Pyewackett and Morning Glory, Maiden Hong Kong, the Schock 40's etc use 55 degree canting keels that with a 20 degree angle of heel get the ballast strut almost horizontal.
There is room to give a lot of design and engineering credit where it is due to the CBTF guys without denying that there is still great room for improvement in mono and multi speed.....

[nico]

About the Cbtf patents, do they exist in europe too or is it only for the States?

Thanks

Don't know the exact answer but if one was to want to violate their patents the market would not include the US; nothing violating their patents could be imported.
I think you can research it under the PCT(Patent Co-operation Treaty).
Why, just out of curiosity?

[nico]

Let me take an example, a Volvo 70 designer wants to use a canting keel with one rudder aft and one foreward. Does he needs to pay the CBTF fee? Is it only for american designer? If yes it would mean that a european design might be less expensive than a american one (I read that the fee is very expensive). Hope it doesnt work like that. Hope does it work for one-off?

Thanks

Patent license fees are generally in the vicinity of 5% of the retail cost of teboat though that can be negotiable. If you were investing in a boat for the Volvo and you wanted to use CBTF why would you not pay the fee and get the best information available on how to use CBTF? There is the chance if the boat stopped in the US and IF CBTFco knew that th boat was using a pirated version of the concept that they could have the boat seized. I don't know the fine points of patent law but I HOPE such a thing would be possible. The rip off of intellectual property is a detestable crime and should be prevented by all means possible.
If the design uses a canting keel and a rudder forward of the canting kee and one aft OR if the boat uses a canting keel and a gybing daggerboard then it violates the CBTF patent. Since I'm convinced that CBTF is the fastest of the lateral resistance solutions with a canting keel there will, I'm sure be more and more of these questions finaly resulting in a major lawsuit. I believe CBTF will win(and hope they do); they've worked out a really fast way to use a canting keel.....