Stability calculations

Circa 1971, we had an even more naive view of warship design than we have today (my friend and I). I am somewhat more sophisticated now, in the sense that I have a better system for computing power curves (actually based on a real system, not some empirical hack). The next issue that I will be tackling is stability. What I want to have is a "back of the envelope" system that is still based on the correct theory. With what I am doing, I am just not going to have the detail to do an exact computation. I would like to do better than what I have been doing (nothing). I would also like to do better than the "Spring Style" program. The "Spring Style" program is a noble effort, and I was really excited when I originally found it and started experimenting. I lost some of my enthusiasm as I found "issues" with it (power calculations, stability, and strength calculations). I felt obligated, since I had criticized it, to do better.