CBTF(Canting Ballast Twin Foil)

Well, I guess since I am reading this stuff, I will post comments and questions:

1. Seems to me that for a boat that has to perform at all points of sail, CBTF is pretty great (probably it's forte is upwind), but for a boat that mostly has to perform downwind, CBTF is not necessarily optimal, because at different speeds you need different sizes and shapes of lifting appendages in the water.

2. I think most daggerboads that are not aligned with the mast also do not come out of the hull at the centerline - they come out to leeward, approximately where the lowest point on the heeled hull is. This improves efficiency.

3. What do you all think about the fact that on the bigger CBTF boats they have to run the engine all the time just to have power to cant the keel? I guess the Schock 40 only has to have the 4 batteries, but the MaxZ86s ran their motors the whole time they were racing eachother in their first race! It seems to me that if the conventional boats in the race were allowed to run their motors while sailing, they would have been going faster as well!

I am fascinated by the technology, and thrilled by the speed, but I am not interested in running my engine while sailing, and I don't want to have to worry about running out of battery power.

4. I agree that an lifting appendage that is heeled produces more heeling moment for the amount of lift it produces than one that is vertical.

 

Happens all the time, unfortunately...

Most patents are unenforceable. The patent office can't be an expert at everything.

 

Drag Racing

I can visualize a cartoon showing two canting keel boats next to each other with 6 or 8 chrome exhaust pipes coming out of the deck on each side and can just hear the noise as the two race their engines before the start!! Still makes me laugh like hell!
But running the engine is a canting keel thing not a CBTF thing. I guess when you want to move large amounts of lead you have to get the power somewhere.
As to patents when it comes right down to it is the responsibilty of the individual applying for the patent to make sure it is patentable. I've done extensive seaches on my own in addition to my attorney's search for the patents I've gotten so feel pretty confident about them.
Since they cost so much to get and to keep it's just foolish not to do the research. I wouldn't count on the " most patents are unenforceable idea".....

 

Do all boats having a rudder aft and one forward of the keel paid a fee to CBTF?
There are several boats coming out from sportsboat to maxis using such appendages.
If not has anybody heard about CBTF doing something against that?

Taking Genuine risk (new Dubois design with Claughton and Oliver) as an example, i think they are going for something similar to CBTf but they dont refer it as CBTF. With their experience and tank test program, i understand that they found useless to get the info from CBTF company.
Any comments?

 

Cbtf

I'm fairly certain Genuine Risk is a paid up CBTF boat and so is Juan K's Maiden Hong Kong. If the boat has a canting keel and twin movable foils ,one in front of the keel strut and one aft it is CBTF paid or not...

 

Patents: Well, I really don't know much about patents, and I guess I was just going by all those rediculous anecdotal stories about rediculous patents...

Engine Use: I guess it seems to me that CBTF boats are specifically being used for bouy racing, whereas other boats with canting keels have generally been used for mostly long distance downwind racing. If you need a little power for a few minutes a day to move the keel so that you can be on one jibe for the day, then I am not really goiing to get up in arms about that. Also, I think all of the canting keel mini transat boats, which I would guess accounts for a large portion of the existing canting keels - have multipart rope systems to cant their keels (a system that would not be fun around the bouys). I think most of the canting keel boats operate on a basis that is a far cry from what happened when Morning Glory and Pyewacket lined up against eachother earlier this month. In some photos you can see the exaust coming out of the transom (although there is no chrome).

 

I notice in the April 2004 edition of the Australian Sailing magazine an article on steering trifoil canting keel designs.

It mentions the use of a "collective" control, which is used to counter the weather helm of the hull by setting a differential "delta" angle between the two coupled rudders.
I presume that more collective angle is applied in stronger winds.

Since weather helm typically increases with angle of heel, how is this effect managed in these new designs? Do they change the collective as the boat heels? Are the two wheels geared together so that you get more collective as you apply more helm?

Very thin hulls generally have less intrinsic weather helm. Perhaps this is just one more reason why the very latest designs are getting even narrower!

 

Collective

Ian,not really a "trifoil": more like two foils and one strut. The foils on a CBTF boat are designed to utilize normal steering by turning in opposite directions and "collective" by turning in the same direction. When collective is properly set upwind the boat makes very little ,if any , leeway. Therefore the canting keel strut can use a shorter chord thicker section that does not produce lateral resistance.Both rudders always turn together even when collective is used and collective can be adjusted for any conditon of balance. The boats like the Schock 40 and Pyewackett /Morning Glory are narrow for their length ; that is standard for a CBTF boat. Canting keel boats particularly CBTF boats can be designed for an optimum angle of heel since that can be maintained thruout much of the wind range by moving the keel.
When I first read "trifoil" in your post I thought you might be going to talk about a canting keel boat with foils; you didn't but it won't be long before that becomes reality: retractable main foil plus rudder t-foil--and a "power flap" on the canting keel strut to develop even more RM when the boat is on foils....

 

so it's really more like the trim controls on an aircraft? Innerestin'
I'm still waiting for the GPS/Doppler Current Detector (tm)/Helm Feeler version with the automatic collective setting to be introduced.

Just kidding, Doug - but it will come, and someone will ask for that soon. "What, I have to _manually_ set the collective based on _feel_?"

Steve "tongue out of cheek now..."

 

auto collective

Steve, I bet it woudn't be too difficult to make an autopilot that would adjust the collective NOW;
all it takes is..well,you know....

 

It would be interesting if someone would do some speed testing to find out if it is indeed the fastest to dial out all leeway with the collective steering, or if having a little leeway is a little faster than no leeway. Perhaps it depends on the boat and on the conditions...

 

I (and two friends) leased Green Hornet in its CBTF configuration from Dynayacht in 1998 and 1999. It was one of the most fun boats I ever sailed. CBTF was outstanding in every wind range and every point of sail. In heavy weather, there was never the slightest problem with any sort of instability due to the "canard" (forward foil) which, in Green Hornet, was linked to the rear foil and tiller with a rigid tube system. The boat has a tiller and it handled exactly like a boat with a conventional rudder except that it had a very light touch, almost no helm, and turned faster and tighter at speed. Steering feel was always sure, positive, and reassuring. The only thing I missed from a conventional boat was that there was little or no helm requiring, it seemed, more concentration to keep a straight course.

Fitted with a "code zero" furling headsail on a sprit, Green Hornet was tame enough for very high performance short handed sailing with inexperienced "light weight" crews or casual bay sails with non-sailor passengers. On one such sail, we snagged a small gust on a very light day, accelerated to near wind speed on a reach, speeding past a Catalina 34 like if she had been anchored. The guys on board the 34 actually "whooped and hollered" (something you usually just see in promotional articles). Like beach cats and trimarans, Green Hornet generated a lot of her own apparent wind on reaches. I would guess from a few experiences that Green Hornet could usually keep up with or beat a Corsair F-24 in light or moderate winds but it was no match for a well sailed F-31. On the other hand, in the Little Ensenada race, with a mostly novice crew and a casual approach, we finished around a J-120, a Santa Cruz 50, a Farr 40, and ... believe or not, a Melges 24 (those little pests are fast downwind).

The CBTF hydraulics and pumps never caused trouble or required service during the 2 years except to top off the fluid. Apart from issues due to the overall age and heavy duty past use of Green Hornet, the only problems we had were related to seaweed, in particular, kelp, which is very thick near San Diego. Kelp was the *only* reason why I decided not to continue sailing Green Hornet. It was a constant hassle to keep the foils free of kelp in San Diego until we got a few miles off shore.

We considered sweeping the foils back to shed kelp but the designers assured us that this would add weight, decrease efficiency and was a generally bad idea. Kelp in San Diego is uniquely thick, common, and nasty. Most local boats have kelp windows and kelp cutting knives. We had short knives on the fore and aft foils but they were difficult to use and we had none on the main keel strut.

Anywhere that thick seaweed is no factor, CBTF boats are an elegant option for combining comfort, ease of handling for day sailing, and exhilarating speed which you can not get any other way except with multihulls. And CBTF boats won't flip or pitchpole like the multihulls can. If you can get a test ride on one, try it. You will be amazed at the ease and the speed.

(FYI : I have no connection with or financial interest in CBTF or any related company. My current boat is a Martin 242 set up to daysail locally (it has a kelp window!) and my next boat will probably be a Corsair tri whose retracting centerboard and rudder make kelp almost a non-issue. For now, the kelp beat me.)

 

Notes from Scuttlebutt:

* From Preston Wake: There is also one other big boat with a canting keel
and twin foil to be launched this year it is Magnitude 80, the Andrews 80.
Although the lead foil is a dagger board similar to a laser.


* From Dave Beck: While I cannot speak for Mike Golding, my guess is that
his KISS solution to his ballast strut problems will be to install a more
robust hydraulic drive motor. The performance advantage of canting ballast
in these light boats is too great to ignore, and the acceptance of powered
ballast struts is a done deal. Every innovative technology goes through a
period where the best engineering solutions are sorted out in the hard,
real world. These solutions then become commonplace and accepted as normal. Anyone who has sailed a performance oriented canting ballast boat knows they are too fast and too much fun to ignore. This is the way to do it.

________________________________________________
I guess I should appoligize to the forum as I should have continued on with this thread rather than starting another under the heading of "Swing Keel 'Fluttering'" , <http://boatdesign.net/forums/showthread.php?t=3839> Just wasn't paying attention.

 

CBTF and leeway

Hi,
Any comments on the effect of Bi-Plane theory on CBTF?...
What about when the leeway comes too zero?...

thanks...

 

oops,
sorry for the basic english mistakes