HELP ! Canting keel for 28ft performance daysailer

[Guest Jan]

Servus !

We are currently developing a 28ft performance daysailer and have some trouble to get valid information about the optimum configuration for the appendages including the canting keel.

The canting keel is needed because the boat will carry 45 sqm (sorry - metric world) upwind, displacement 1650kg and will only carry a crew of 2 or maximum 3. So for performance sailing we need a canting keel in order to get enough upright moment (correct word ?)

So far we know that there are several options

"Classic CBTF" with controllable forward foil. This seems to be too much mechanics etc for a 28ft

Twin daggerboards (as used on future Volvo 70s). This might be great for racer but not for a fast yet comfortable performance daysailer. Not enouigh space under deck anhow

Canting keel with forward daggerboard. This seems to be the worst for the upwind performance and the influence on the sail plan

The 1mtr class boats seem to be playing aroud with with on the keel bulb. Does it work and if so would this work on a 28ft "real" sailboat ?

Please make any comments on what you would recommend as the best appendages configuration for a 28ft baot. In case you have any drawing or papers we would be more than happy to get those. Obviously postage is on us.

Thanks again


Jan
Berlin, Germany

[Guest]

From the length disp SA, i think it looks like a small IAAC ? On the heavy scale but highly canvassed. No Beam value are given but must be small. From a performance point of view, i think CBTF is the way to go. But it must be difficult to handle and use. I think for such program, a single gibing centerboard is the way to go, it will be deeply immersed (high beam/ canoe body draft) and wont ventilate. For such narrow hull, twin daggerboards arent required. A daggerboard in front of the keel stepped mast doesnt take much room.
Finally, i think you were referring to winglets (big) on the keel. It needs to be researched. Might be interesting.

Nico

[Guest Jan]

Sorry about the beam dimensions.

The basic layout looks like 2.1 or 2.2 meters beam at the waterline. The deck beam will be 2.8 meters.

The displacement is because we need to get the boat trailerbale. And even a BMW or Mercedes does not take more than 2.200kg incl. a trailer with 450 kg

Jan

[Guest]

I have a few thoughts on the canting ballast. Since I have never owned a boat with canting ballast and have never sailed one either, I may be way off base but here is my 2 cents. I think the hydraulic and electrical systems are much too complicated and expensive on boats like the Schock 40. I think you should let gravity do most of the work and only have a small hand hydraulic pump as backup. Eliminate the electrical hydraulic pumps completely. The hydraulic cylinder attached to the ballast could be setup to act as a dampener so that the ballast gently swings and can be hydraulically locked in position. By releasing the ballast just before tacking, it will swing downward and be locked. The boat will heel which initiates the tack. Once on the new heading the ballast will be positioned to the correct side and can be adjusted further with the hand pump if needed. This is similar to how the water ballast is used.

[nico]

Is it a one off?

[Guest Jan]

It is a prototype for what we hope becomes a series. It is a niche product. Compare it to a 911 Porsche


Jan

[jonathan]

Hey, jan, I think some people got the same idea as you. Maybe you can find your answers there:
http://www.nacira-design.com/Portfolio/racing/N26.HTML

[Doug Lord]

Jan, for the highest performance you should seriously consider CBTF: best VMG upwind using collective steering plus other important benefits. Contact Bill Burns at info@cbtfco.com
If you subscribe to "The Daily Sail" and maybe even if you don't(they have a free tour I believe) go to their front page and click on the pix on the right showing the canting keel and take a look at Full Pelt: it uses a canting keel but with the daggerboard AFT of the canting keel. That way when the keel cants the shift of the clr is in the right direction--at least thats their justification(that would suggest that their daggerboard is not a gybing board and that both the canting strut AND the daggerboard are developing lateral resistance-not good if true). Back to the begining for a second: one of the most important design considerations in CBTF and it should be in any canting keel application is how to keep the appendage wetted surface down. CBTF solves this by using "collective steering" which allows both "rudder" foils to be turned the same direction upwind eliminating leeway 100%. That in turn allows the canting keel strut to be designed with a lower wetted surface than would be possible if the keel strut itself also had to generate lateral resitance. Furter drag reduction comes with the fact that the hull is now going straight thru the water instead of sideways.
The next best to CBTF is a gybing daggerboard and it could be placed in front of or behind the canting keel. But don't choose this option because you don't want to pay the CBTF royalty: their patent covers a gybing daggerboard used in conjunction with a canting keel.
A boat called Bondi Tram was recently launched in Australia: it uses a canting keel with wings similar to those used on th bulbs of IACC boats but specifically designed to provide lateral resistance upwind as the keel cants. Disadvantage: they're still there when you don't need them.
So from a performance perspective CBTF is best followed by a gybing daggerboard. A non -gybing daggerboard is a bad idea-don't even consider it.
As to CBTF not working on a 26 footer : that is a myth-- I'm using it on a new line of RC one meter called the F100CBTF and it has been designed using the most modern analysis available and the numbers show that it will work very well...

[Guest Jan]

Thanks for all your input. But I am still not convinced about CBTF on a 28ft boat.

Two aspects: The forward rudder is pretty far away from the keel so in the moment we cant the keel the whole lateral area will change dramatically and the boat will begin to "jump" to windward (or leeward ?)

The other aspect is that the engineering and construction efford is pretty high for this kind of "double steering". Synchronisation etc. Sound slike a lot of testing.

If CBTF would be the choice why do the Volvos go for twin daggerboards ? Just because of the wetted area when downwind ?

What do you think of this solution (http://www.sailinganarchy.com/general/2003/smak2.htm). It comes from an australian boat. There the daggerboard is very close to the keel.

The only question is if it is necessary to use a daggerboard. The alternative would be a fixed finn with appr. 100kg. Would make you feel more comfortable. Yes, it is slower downwind. But does it make it big difference whether you are planing with 14 or 16knots ? On a dayracer.

BTW: Does anyone of you have experience with the hydraulic system etc ? Seems like a big secret.

[Guest Jan]

Thanks for all your input. But I am still not convinced about CBTF on a 28ft boat.

Two aspects: The forward rudder is pretty far away from the keel so in the moment we cant the keel the whole lateral area will change dramatically and the boat will begin to "jump" to windward (or leeward ?)

The other aspect is that the engineering and construction efford is pretty high for this kind of "double steering". Synchronisation etc. Sound slike a lot of testing.

If CBTF would be the choice why do the Volvos go for twin daggerboards ? Just because of the wetted area when downwind ?

What do you think of this solution (http://www.sailinganarchy.com/general/2003/smak2.htm). It comes from an australian boat. There the daggerboard is very close to the keel.

The only question is if it is necessary to use a daggerboard. The alternative would be a fixed finn with appr. 100kg. Would make you feel more comfortable. Yes, it is slower downwind. But does it make it big difference whether you are planing with 14 or 16knots ? On a dayracer.

BTW: Does anyone of you have experience with the hydraulic system etc ? Seems like a big secret.

Jan

[dougfrolich]

I am working on an ocean going 30 foot swing keel, so I have been working out some similar issues. Like you, I do not think the forward rudder is the most elegant solution. I will go with either a single centerline daggerboard or twin asym canted dagger boards like open 60's. I'll post more as the design develops. Do you have any drawings? Sounds like a great project!