CB vs keel

[Quoddy]

I have heard it said in many places that a centerboard will never go to weather as well as a keel.
If the underwater foil is like a sail then most of the lift should be near the leading edge. If this is so then it would seem the overall size or length fore and aft would make little difference? Or is the superiority in the ability to carry more ballast and therefore more sail?

 

[Snotter]

The statement may be true for a given area below the water line. However, you can more than compensate by making a center (or dagger) board deeper without feer of constantly running aground.

 

[tommays]

The shape of the foil in both the keel and rudder (even on kids opti prams)has a big impact on performance

We have a custom keel and rudder(kind of a V2) and cant go to the V3 rudder because the racing rating hit is so big because of the performance difference in the 3 possible rudders

 

[Dan Johnson]

Centerboard vs Keel...

I race on a centerboard boat and can say it doesn't point quite as high as the boats with ballasted keels. Both a J24 and a Catalina 32 point higher than we can. It is more tender and requires close attention to sail trim to optimize performance, and benefits from rail meat in heavier air.

On the plus side, we can raise the centerboard on down-wind runs to reduce drag, but, under the asym the boat gets a bit "wobbly" with wind shifts so we keep it down when flying the asym.

 

[plchakcer]

Pointing up wind is a compromise. Sailing downwind raise the board and run a bit faster. Where you sail is the key to this question.

 

[Prime Time]

It's all about compromises

"I grew up" being very biased against centerboards but times do change. It all depends on where you sail and where you want to go and what are your priorities. Some keel centerboard boats sail very well.

My Bristol 43.3 only draws 4.5 feet with the board up. Board down, we draw almost 11 feet which does improve the ability to point and decrease lee-way substantially. That being said, we certainly don't point as well as a real racing design with an 8 foot deep fin keel with a bulb on the bottom. However, putting the Board down improves pointing by about 8 degrees.

Where we sail on the Raritan Bay, it is very nice having the shallow draft.

Sailing downwind on a reach in 15Knots apparent with the asymmetric chute up, board up, we are very competitive with much faster boats that owe us time in PHRF. In a recent race on Raritan Bay, we were actually ahead of a J 105 and ahead on time with a Beneteau First 40 during a 6 mile downwind leg (first leg of race). Up wind, they walked away from us as their ratings (and design) suggest they would.

 

[Prime Time]

Keel Shape

I missed your question at the bottom of the post.

The shape of the foil may be very important to the performance.

Centerboards may not weigh very much to be effective. It isn't all about lowering the center of gravity like on a swing keel.

 

[Prime Time]

Further info

Sorry to keep on breaking up the reply but:

It is an issue of drag vs. lift according to my friend who is a fluids dynamics guy. The shape of the foil impacts that relationship. The keel "flys" underwater.

I used to try to get him to put my Flying Scot in his flow tank at Rutgers to check out different bottom preparations. Never could get a grad student interested in the project. His bias was that the only part of any foil or hull in the water that mattered in terms of surface characteristics was just the leading edge, due to turbulence that would start to develop.

 

[Barnacle Bill]

I think it depends on the type of keel you are referring to, or comparing to. Obviously a Cape Dory full keel with barn door rudder won't sail to weather as well as a J/24 or J/125. Windward performance has a lot to do with how deep you are going and then the shape. Some centerboard or swing keel boats will sail into the wind better than most shoal draft, or winged keel production boats. The French designed Ranger 23 built by Bangor Punta had a retractable keel on a worm gear that was very effective upwind. Better than most. The S-2 7.9's or 6.9's which have retractable keels go to weather very well. The new J/95 with shoal keel and bronze centerboard with twin rudders sails to weather very well (and they are now coming out with a new J/108 of the same underbody shape). The water ballasted Schock 23 had a swing keel and it sails very well to weather.
I think it is safe to say a boat with a keel appendage that sticks deeper in the water will sail into the wind better than a keel that is shallower in design. A Catalina 22 with a swing keel (and it is a pig keel in terms of shape or lack of it) will sail into the wind better than most any boat with a shoal keel. A deep fin blade with a lot of lift will be the best for windward performance. But, you know a Catalina 22 will blow the doors off of a J/109 in 3 feet of water.