I think the problem with your calculation is that you are entering the draft of the keel; not the hull draft. For a Catalina 42 the hull draft should be somewhere in the range of 1-2 feet and that would give an AVS result somewhre in the 118-130 deg range.
Use the following page for entering numbers; remember to use hull draft not keel draft:
Thanks for pointing that out -- yes, I was using total draft, not hull draft. I was actually working from the formula that Nottoway had linked to -- I didn't realize there was an interactive site that would do the work for me. Very handy!
One problem, though, I know the total draft (hull and keel) of our boat, but not our hull draft without the keel.
I could guess, but that wouldn't be very scientific.
Actually, I'm surprised that the formula does not want the keel draft -- seems like that would be a major component in stability.
Also, I posted the Intact Stability Curve for the Catalina 42 just as an example. We don't actually own one. That curve was generated by Catalina Yachts and the designer, so I have to assume it's a more comprehensive calculation (such as JeffH described above) and reasonably accurate.