Angle of Vanishing Stability:
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 dinghy 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.
The following is the formula used to calculate The Angle of Vanishing Stability:
Screening Stability Value ( SSV ) = ( Beam 2 ) / ( BR * HD * DV1/3)
BR: Ballast Ratio ( Keel Weight / Total Weight )
HD: Hull Draft
DV: The Displacement Volume in cubic metres. DV is entered as pounds of displacement on the webpage and converted to cubic metres by the formula:
( Weight in Pounds / 64 )*0.0283168 = Displacement Volume in Cubic Metres
The Beam and Hull Draft in this formula are in metres. These values are entered in feet on the webpage and are converted to metres before SSV calculation.
Angle of Vanishing Stability approximately equals 110 + ( 400 / (SSV-10) )
Adapted from: K. Adlard Coles and Peter Bruce (eds.) Adlard Coles’ Heavy Weather Sailing, revised 3rd edition, chapter 2: ‘Stability of Yachts in large breaking waves’, pp11-23, International Marine, Camden, Maine 1980.
Capsize Screening Formula:
The following is used to calculate the Capsize Screening Formula:
Capsize Screening Formula = Beam / (Displacement / 64)1/3
Displacement is in Pounds
Beam is measured in Feet
Adapted from: John Rousmaniere, The Annapolis Book of Seamanship, chapter 1: ‘Boat Selection’, p35, Simon & Schuster, New York (edition uncited).