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This formula gives an estimate of the angle of vanishing stability or the angle the boat can heel and still right itself.

This is the resistance to capsize and heel.  One of the best predictors of ultimate stability is the "angle of vanishing stability" or the angle to which the boat can heel and still right itself. A dingy will have a stability range of about 80 degrees, an inland water boat should have a stability range of 100 degrees, and an offshore boat of at least 120 degrees.  Boats which have a stability angle of less than 140 degrees may be left floating upside down once capsized.  Boats with a higher angle will usually right themselves
     

    
1
.  Enter Widest Width of Boat (Beam) in Feet:  

2.  Enter Total Weight in Pounds:   

3.  Enter Ballast & Keel Weight in Pounds: 

4.  Enter Hull (not including the keel) Draft in Feet: 


     
Reference:  K. Adlard Coles' and Peter Bruce's (editors)   Adlard Coles' Heavy Weather Sailing   (30th edition)  Stability of Yachts in large breaking waves.   Chapter 2   pp11-23   International marine,  Camden, Maine
    


    This formula does not fully take into account the vertical position of the center of gravity (VCG).  The VCG can be lowered by a longer keel or by having more ballast (weight of the keel) at the end of the keel.  However, according to Adlard Coles' "Heavy Weather Sailing"  thirtieth anniversary edition, "The effects of large movements of the VCG on the propensity to capsize was surprising small".   Nevertheless, a low VCG will greatly help the boat in righting itself once it has capsized.  Thus, boats with a long lead keel or a lead bulb at the end of the keel may have a higher angle of vanishing stability than that predicted by the formula.  

A caveat regarding stability predictions:  One of the greatest sailing disasters in recent maritime history, the 1998 Sydney-Hobart Race, offered a number or lessons regarding the performance of sailboats and crews in heavy weather conditions.   The 1998 Sydney to Hobart Race Review Committee report, summarized by Peter Bush, the committee chair, reported the following as one of the significant findings:  "There is no evidence that any particular style or design of boat fared better or worse in the conditions.  The age of  yacht, age of design, construction method, construction material, high or low stability, heavy or light displacement, or rig type were not determining factors.  Whether or not a yacht was hit by an extreme wave was a matter of chance."    (Ref:  Rob Mundle in Fatal Storm,  Publisher's Afterward p 249.  International Marine/McGraw-Hill  Camden, Maine.)

According to Andrew Claughton  in Heavy Weather Sailing 30th ed. p 21  "This (the test data presented in the chapter) suggests that alterations in form (of a sailboat) that improves capsize resistance may be rendered ineffective by a relatively small increase in breaking wave height."

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Copyright 2001         Website last updated 05/11/2005