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Go Back   SailNet Community > General Interest > General Discussion (sailing related)
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Old 03-19-2001
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Self-righting

Hello,
I''m new to sailing so apologies if this is a
dumb question.
Is there an easy way to tell if a boat is self righting in a capsize by looking at
figures like ballast, displacement etc?
At the moment I am learning in (on?) toppers
these capsize easily ( well, they do when I sail them ) and do not self right - but that is part of the fun. Single handing bigger boats, say 16 to 22 ft, this could be a problem.

Thank you for any info.
Paul
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Old 03-20-2001
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Self-righting

I think most manufacturers can tell you if their boat is self-righting. I grew up sailing a San Juan 21 and the manufacturer said it was self-righting. After sailing the boat for years, I had a sudden squall hit me once while I was beating into the wind. The boat went over, the sails hit the water, and in a fraction of a second, the boat popped right up. After experiencing this, I always felt alot safer sailing the boat in heavy winds. I think for most people this should be a rare event. It happened only once in my 20+ years sailing the boat. The time it happened, my single crew member was inexperienced, and he didn''t let the jib sheet go quickly enough. Good Luck. Rob
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Old 03-24-2001
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Self-righting

Self righting is a comparative term. All boats have a point at which they are stabile upside down. In most keel boats that point comes between 120 and 140 degrees of heel. In unballasted boats that typically occurs somewhere around 80 to 90 degrees of heel.

The statically calculated angle of "ultimate stability" or "negative stability" for a production boat is a pretty inexact number as it is affected by the way the boat is equipped and loaded. Because the calculation needs to include factors related to hull and cabin shape as well as weight distribution it is also a pretty elaborate calculation.

There are a variety ''surogate'' formulas that try to apporximate the ultimate stability of a particular design but because they ignore the two most critical factors in determing stability, namely the locations the center of gravity of the boat and the location of the boats center of bouyance over a wide range of heel angles they are terribly misleading.

These formulas primarily focus on secondary factors affecting a boat''s ultimate stability as Follows:

Beam- Wide beam contributes to a boat''s stability when it is standing up straight but as the boat heels beam becomes a liability to the boats ultimate stability.

Weight- Weight adds to a boat''s inertia (a heavier boat feels more stabile when you step aboard from the dock) but weight really does nothing for stability in an of itself. If that weight is carried high, (in teak decks, heavy hull, hull rig and interior furnishings) as it often is in heavy cruising boats, it can actually result in pretty poor ultimate stability. Surogate stability formulas use weight a major determinant but without the vertical center of gravity being taken into account that info is useless.

Draft- All other things being equal, the deeper the center of gravity the greater the ultimate stability. Deeper fin keel boats, with their lower center of gravities often will generate greater stability than their heavier bretheren.

So back to your question. Generally keel boats are advertized as being self-righting and unballasted centerboarders are not. You will sometimes see surogate stability numbers published. Bigger race boats that have been certified under the IMS racing rule have a calculated ultimate stability on their rating certificate that is a reasonably close to correct number. Otherwise assume that to a point a ballasted boat will be self rescuing and an unballasted boat will not.
(One more aside- boats with water ballast and other low density ballast materials tend to not have great reserve stability.)

Does that Help?
Good luck
Jeff
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