Shallows in a swing keel - Page 2 - SailNet Community
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post #11 of 22 Old 08-30-2007
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There is a big difference between a centerboard and a swing keel with 400lbs of lead on the end of it. The former may play around with differents settings. The latter isn't worth a tinker's damn, motoring or sailing with the keel retracted at all. The entire trim of the boat is radically changed.

Since we are generally talking about drafts under five feet I really do not see great advantage. In decent weather, you'd not only want the keel down, but pinned as well.

The only time I crank my keel up is if I am going to beach the boat or after I've run hard aground. If you want to sail in water skinnier than that you either need a different boat or you should do it only with a 150 genny and winds over 20kts so you can keep her heeled thirty degrees of so. (g)

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post #12 of 22 Old 08-30-2007
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I have a Helms 25 that draws 20" with the centerboard up. The fixed keel that makes up the 20" draft is ballasted. The 300 pound cast iron centerboard draws 6' all the way down. If this design is close to yours, the centerboard makes a big difference in weather helm. At about 1/3 down my boat is balanced in a 10 to 15 kt wind. However it can be sailed easily all the way up.

Wayne
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post #13 of 22 Old 08-30-2007
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Quote:
Originally Posted by bobmcgov View Post
ETA: Gosh, Andy -- all that's missing from that chart is the minefields, giant whirlpool, and a kraken or two. Should keep you on your toes!
The minefields aren't marked for security reasons. The Krakens are south of the chart's coverage.

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post #14 of 22 Old 08-30-2007
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I have a 1983 Catalina 22 with a swing keel that was replaced with the previous owner. I have found with the keel up the boat will still point fairly well even in mild winds. You have to remember that the keel is ballast in addition to keel. What kind of boat do you have?

-Spencer
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post #15 of 22 Old 08-30-2007
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I have a 21' Cal if it is I you are addressing. (g)

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post #16 of 22 Old 08-31-2007
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Spencer: My questions refer to the San Juan 21, which has no stub keel. Just a 420lb, 4'-draft, fully-retracting centerboard. I'm presently sailing a Buccaneer18, which has 3' of draft with the board down and heels faster than a champion bird dog.

The SJ21 manual promotes raising the keel half way up when reaching or running. But it says never sail w/ it all the way up, which makes sense -- that would put your ballast above water line. Seldom a good plan! (Tho I guess that's how dinghies sail all the time....)
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post #17 of 22 Old 08-31-2007 Thread Starter
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SA SAilor,

I have a Newport 17. It has some concrete ballast plus the steel swing CB.

Bob,

The 2 days I sailed a Bucc I never got all that much wind but I think I dipped the mast when I sneezed once. They are quick little boats. A friend on a PWC clocked me at 6 reaching in what I thought was a fairly light breeze.
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post #18 of 22 Old 08-31-2007
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A ballasted keel provides lateral resistance, which tends to prevent the boat from side-slipping when it's sailing to windward, and it provides a weighted lever, which resists heeling. There are all kinds of swing keel and centerboard configurations. Some designs use a swing keel that retracts snugly up against the boat's bottom, like a CATALINA 22 OR 25. When that type of keel is retracted, it greatly reduces the keel's effect as ballast (to resist heeling), but the retracted keel still provides a great deal of lateral resistance. When that type of keel is fully retracted, the same amount of surface area is still submerged in the water, and it still provides nearly the same amount of lateral resistance. IOW, Retracting this type of keel doesn't significantly reduce it's lateral resistance.

By comparison, some boats carry their ballast in a centerboard trunk, which can't be moved. They often have a centerboard or daggerboard that swings or is raised up into the centerboard trunk. If the entire surface of the centerboard is retracted into the centerboard trunk, so that the water is no longer flowing across the surface area of the centerboard, then retracting this type of keel significantly reduces it's lateral resistance. Of course, the centerboard trunk itself provides lateral resistance, but, to the extent that the centerboard surface is retracted into the trunk, the amount of lateral resistance is reduced.

So, the effect of raising or lowering a swing keel depends very much on how it's designed.
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post #19 of 22 Old 08-31-2007 Thread Starter
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I think the Newport 17 has roughly 300 lbs of ballast in the hull and the board weighs somewhere between 100 and 150 (the reason for the rough estimates is that due to replacements, repairs and differences over model years, they don't all match). I drop the board a few inches to rest on a board on the trailer to take strain off the cable while towing and it looks like a reasonable skeg.

Last edited by arbarnhart; 08-31-2007 at 03:22 PM.
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post #20 of 22 Old 08-31-2007
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Actually some of swing keel boats have used those swing keels for lunch hooks, Amongst other things.
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