CBTF(Canting Ballast Twin Foil)

So it means that a fair part of the mini 6.50 (say 1/4) are violating the CBTF patent? (as they use gybing daggerboard and canting keel)

An interesting article http://www.sailinganarchy.com/general/2003/cbtf_bogus_rebuttal.htm

 

Patent Infringement

It's possible that the patent is being violated or perhaps they paid a license fee; whatever the case I'm sure CBTFco is on top of it.....

 

I don't think there is any chance of having the boat siezed. A patent is issued after investigation as to the originality of the invention by the patent office - those guys are good, but often not experts in the field of the patent. An issued patent may not hold up under challenge for a number of reasons - the main one being the existance of prior art. If the patent holder feels that someone is in breach then they can file suit and you go through the process of determining if there has been a breach or not. If there has then a license fee and fine usually result, sometimes the patent becomes worthless...

As for the protection of intellectual property through patents - they were introduced into the US constitution as a mechanism for the spread of ideas - a teaching device.

It would be interesting to see if the CBFT guys would file suit on a aleged infringement as the gybing boards mentioned earlier could be construed as prior art - then the patent is gone. While it remains un-tested they can continue licensing it to those who want to use it

 

Why would twin daggarboards not only be as fast, but faster than CBTF?
-The CBTF foil is symetrical...no such limit for twin daggarboards. Less induced drag and greater lift.
-The CBTF foil is heeled and loses flow and projected area...the daggarboard is vertical when the boat is heeled.
-The CBTF foil doesn't ever get removed to reduce drag, the daggarboards can be pulled up entirely (or partially) to suit the conditions.

So given these facts, how can it be that CBTF is faster upwind in every condition?

 

Cbtf: Collective

Much of the "facts" you mentioned were not facts at all-more like a misunderstanding of CBTF.
CBTF upwind uses "collective" steering which allows the leeway of the boat to be dialed out in all conditions.Collective steering allows both foils to be turned the same direction while for normal steering they turn opposite directions. Twin asy daggerboards are only exactly right for one condition. CBTF boats are usually designed for an optimum angle of heel which can be controlled relatively precisely with the canting keel.
By dialing out leeway the hull goes straight thru the water reducing drag. The canting keel strut also can be designed with a shorter chord, thicker section since it develops none of the lateral resistance. By using extremely high aspect ratio on the twin foils their area is kept to a minimum.
And finally CBTF gets a reduction in wavemaking resistance due to the PLACEMENT of the twin foils that no other lateral resistance solution offers.

 

Good question

My final year dissertation is mainly about the comparaison of CBTF and twin daggerboards on a Volvo 70. It involved using the towing tank, so i gained a good insight in the problem.

this is not exact. The daggerboards produces the same lift for a similar draft. Therefore the induced drag is similar. Viscous drag might be a bit lower for the same lift. However CBTF shares the lift on two appendages and fair gain can be expected in induced drag.

Most current boats needs to generate sideforce even downwind. (asymetric gennakers,etc...)

I dont think it is The big thing about Cbtf, it is probably the most marketed "advantage". But leeway is actually important since a hull/appendages interaction is beneficial.

I think this is the main problem with daggerboards.


When finished i ll post my dissertation, hope it ll give more insight in this interesting area.

 

Nico, thanks for the straight up answers. Allow me to clarify a few statements for further consideration.

At higher and higher speeds, while we still need some lateral resistance, we need less and less area to resist that. So we raise the daggarboard, not all the way, but maybe 40 or 60 or 90%. We could raise our rudder as well (some do) but that's a separate issue.

Now Doug, I'd like some more explaination of this wavemaking resistance. It's my understanding that this is the same way that the bulbous bow works on a cargo ship or tanker. But as you mention in disparaging the daggarboard idea, it is tuned to one speed only. Is that not also the case with the unique wavemaking resistance reducing charactaristics of CBTF? Like a tanker ship running a some speed other than it's design speed, won't a CBTF boat suffer greater drag due to the foils wave train operating outside their design speed?

One issue neither of you gentlemen address is the fact that twin daggarboards the boards are 'plumb' when the boat is heeled, while the canard foil is inclined at the heel angle of the boat. Nico, I'm sure this will be answered in your dissertation, I look forward to the results, and I hope you will share them with the group.

Last question Doug, what happens when I strike a container or a whale with that forward rudder. What sort of contingency plans are in place for this eventuality?

Thanks for the feedback guys. This is a great thread.

 

The main problem with raising the daggerboard is that it reduce the effective draft by a large amount. The increase in induced drag is not made up by the decrease in viscous drag, except at low speed.
CBTf has a fair influence on wave making obviously it s the most effective for one speed only (when the forward rudder is below the bow wave) therefore around Fn 0.35 so most of the upwind sailing.

The canard foil is reducing the righting moment, the daggerboard is not this is something that is difficult to include with common VPP. I am writing a vpp to accomodate such things but i dont know yet how much does it influence the results.

 

Cbtf

Nico, how does CBTF's forward foil reduce righting moment and a dggerboard does not?
One of the areas also touched by CBTFco is using a flap on the canting keel strut to increase righting moment. I've done model experiments on a design for a canting keel hydrofoil with a retractable main foil and at speeds you can drastically increase righing moment by using the strut in this way. I'm not sure how it will work at upwind displacement speeds but they do have a patent on it.
As to hitting objects and a clearer explanation of the wavemaking advantage you should probably contact Bill or Bruce at CBTFco.
I've got a patent pending on a system I call kFOIL™ that basically consists of a pivotable foil mounted IN a slot in the BULB. When the foil is deployed it makes up for lost lateral resistance from the canting keel fin and can be automatically deployed or retracted.Fixed wings like IACC wings have been used on Atomic ,a 52' Sydney Harbor Racer, designed by Andy Dovell in Sydney, Australia. I called him and he is convinced such wings are a good(very fast) solution for canting keels. My version is similar except that in light air or downwind the "wing" or wings 100% retract.....It's primary advantages are in not taking up room inside the boat as well in being abe to retract if hit by something and it may have others(including speed) I haven't explored thoroughly yet.It can be used on low aspect fixed keels to improve weather performance..
But the king of lateral resistance solutions for now seems to be CBTF....

 

It s how i see it Blue vectors are of the same magnitude, assuming same righting moment for the two boats, the sail side force and keel side force are equal for the two boats. However the cbtf rudder is producing lift at an angle, therefore the required lift is sideforce/(cos(heel)) this is not the case for the daggerboard. Green is therefore bigger than Red. So CBTF produces more heeling moment. Hope the diagram help
Another way to see it, is that the cbtf rudder is producing an upward force increasing heeling moment. The daggerboard is not.

 

Cbtf

Seems to me both foils produce a moment about the CB of the boat opposing righting moment.
Your drawing illustrates the fin and keel bulb which may be misleading since with a CBTF system the the keel strut develops no lateral resistance. What I think you were trying to illustrate was the more or less horizontal force produced from the lee of two asymetrical daggerboards(at one particular angle of heel) but usually that board would be at a preset angle of incidence-as is the CBTF foil(though not preset). A fixed center daggerboard would be at the same angle of heel as the CBTF foil.I guess there is some confusion as to whether you are talking about the angle of heel of the board/foil coupled with angle of incidence or just angle of heel? And were you illustrating the twin asy board idea compared to CBTF? At any rate,the significant moment is that about the CB opposing righting moment while developing lateral resistance, right? The lift(vertical) componnet of that would be of no consequence unless I'm missing something?
In your analysis did you look at all at wings on the bulb as a lateral resistance solution?

 

Yes my drawings are a bit misleading. I should not have drawn the bulb there. The one on the left represents the CBTF and on the right two asymetric daggeroboard system. A central daggerboard will have the same effect as the CBTF.
Most of my analysis were done on the comparaison of these two configuration.Mostly because the volvo rule doenst allow for such things. To study the other possibilities i would have needed more towing tank or a more developed VPP (which i am writing now). My project is actually the complete design ( structure, hull design, rig etc....).

 

About the central daggerboard, there are one or two mini 650 which have a swinging daggerboard. The daggerboard can be moved deeper at the required angle. I think this one hasnt been patented by CBTf (yet )

 

I'm a big believer in the trim tab on the canting strut for added righting moment, but I don't imagine that patent will be enforceable. I posted that idea and discussed it at some length four years ago on the Mini 650 forum. That would be for the lawyers to sort out, but this business of patenting ideas that are already public domain is kinda lame.

 

Patents

Patenting something "in the public domain" is a sure way to waste money(if it can be done which is HIGHLY unlikely). No one with any brains would spend the effort-and money- on a patent without doing extensive research on their own and having an attorney do an exhaustive search. It's also true that there is more to some patent's than initially meets the eye.