capsize screen?

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Ben

This is my first time looking through this site (I think it's great, btw) and I was checking out the ratings for my capri 22. I just wondered exactly what the capsize screen means.
 
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RonD

Capsize Screening Formula (CSF)

The CSF is a general Rule-of-Thumb regarding the stability of vessels. Expressed another way, it's about a vessel's ability to (a) resist being capsized and (b) quickly right itself after being capsized. The CSF was developed as a comparison tool. As such, and because it isn't an "absolute" design calculation, it is one factor used to weigh various aspects of boat designs against intended use. In this case, "capsize" is predominantly an offshore sailing concern -- a "heavy weather" combination of high winds and big seas that can knock a boat over. The formula used is: CSF# = BEAM (in feet) divided by the CUBE ROOT of [DISPLACEMENT (lb) divided by 64]. A CSF# less than or equal to 2.0 is considered "good" for offshore operation -- the lower the better for stability. Another measurement/calculation often used is the Limit of Positive Stability (LPS), expressed in degrees of roll relative to perfectly level/upright (0 deg) and totally inverted (180 deg). It is often shown graphically as the righting moment-arm force (Y-axis) vs. roll angle (X-axis). An LPS of greater than 120 deg is considered necessary for offshore use. The greater the LPS angle, the more "unstable" the boat is while inverted ("turtled") and the faster it will right itself. LPS and CSF are obviously related in some way. Suggested reading: "The Desirable and Undesirable Characteristics of Offshore Yachts," published by the Cruising Club of America (CCA), and widely available in bookstores & chandleries. It reflects the results of much testing, analysis, and debate following the disasterous Fastnet Race 20-some years ago where many boats were damaged or sunk in a storm. Now, having said all that you must put it into perspective: what type of boat do you have and what do you use it for? Wind alone can knock you down close to 90deg, but not capsize you (unless your LPS is 90deg or less, or your spars "dig in" to the water and your forward motion on that sideways force causes a spiral roll). Very large and steep waves can capsize you, as can the combination of winds & waves. A Capri 22 isn't a boat designed for offshore use, but is well suited for sailing more protected waters. My C320 isn't a true offshore boat either, but is well suited for coastal cruising where I can weather isolated T-storms, or moderate winds/seas, but duck for shelter to avoid major storms at sea. Hope that answers your question. --RonD
 
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