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**To**:**smkranick@xxxxxxxxxxx, sanjuan23@xxxxxxxx****Subject**:**Re: A tech few questions****From**:**Wesharp3@xxxxxxx**- Date: Tue, 5 Sep 2000 23:29:52 EDT
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Sean, Some answers to your questions: 1) I have been reading a book titled "Heavy Weather Sailing" by Peter Bruce. In it he devotes a chapter to the stability of yachts and presents an imperical formula. It is called the Angle of Vanishing Stability (AVS) and is approximately AVS ~110 + 400/(screening value -10) The screening value (SV) is given as SV = B^2/(RxTxV^(1/3)) where B is the maximum beam in meters, R is the ballast ratio: keel weight/total weight, T is the hull draft @ B/8 from centerline in meters, and V is the displacement volume in cubic meters = Displacement (kg)/Density of water (1000 kg/cubic meter). For my 1977 SJ23 I calculated the following: B = 2.44 meter, R = 0.343, T = 0.279 meter, V = 0.123 cubic meters, giving SV = 57.97 (no units) and AVS ~ 118 degrees. A number of boat types with their righting moment and AVS are plotted in his discussion. For a long keel the AVS is about 160 degrees with maximum righting moment about 50% of that or 80 degrees. For a fin keel boat of low freeboard the AVS is about 135 degrees with the maximum righting moment about 48% of that or 65 degrees. The higher the Vertical Center of Gravity (VCG) is above the intersection of the keel with the hull, the smaller the AVS. The SJ is not a fin keel boat and is not a long keel but some where in between with a low free board. From the low number for the AVS I would judge that the VCG is above the water line. At any rate 50% of 118 degrees is 59 degrees for the maximum righting moment. Any angle up to 118 degrees and the SJ will right itself. If the SJ is broadsided by a wave and rolls past 118 degrees, then it is going to roll over. 2) Knowing my mast height above the forecastle and scaling from the drawing in my owners manual I would judge that the height from water line to mast top is near 34 feet. Bill Sharp San Juan 23 Internet Fleet: http://www.geocities.com/Yosemite/Rapids/5493/ San Juan 23 Tech Tips: http://www.geocities.com/Yosemite/2358/index.html mailing list commands: mailto:majordomo@peak.org?body=help

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