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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