when does CSF make a difference?
There is absolutely no useful imformation that can be gleaned from a boat''s Capsize Sreeen Factor. With the possible exception of beam, the capsize screen factor includes absolutely none of the factors that really control the stability of a boat. It does not include the vertical center of gravity, buoyancy and weight distributions, drag, sail area and sail area distribution, hull shape or windage.
The example that I typically give regarding the dangerously misleading nature of the Capsize Screen Formula is this one, if we had two identical sailboats except that one had a 1000 lb weight at its masthead, (and yes I know that no one would ever put a 1000 lb weight at the top of a mast) the capsize screen formula would predict that the boat with the weight at the top of its mast would be less likely to capsize while in reality it would be way more likely to capsize.
The reality is that heavier displacement boats appear to be more stable when in reality, they often lack stability relative to their drag making them less stable than lighter craft with more easily driven hulls and lower center of gravities especially as viewed relative to their centers of buoyancy.
A much more accurate indicator of stability is the CE''s STIX (Stability Index) but it is by far a more complex set of formulas to calculate.
Rod Johnstone had an interesting discussion of stability on the J-boats website that compared the Capsize Screen Factor with the actual stability of actual boats and pretty much showed the irrelevance of the Capsize screen factor.