Values less than 2 are good. The formula penalizes wide boats for their high inverted stability and light weight boats because of their violent response to large waves. All multi hulls, some modern coastal cruisers and many racing designs have problems meeting this criteria. Anything over 2 scores zero. This is an empirical term developed by yacht designer Ted Brewer.
Large numbers indicate a smoother, more comfortable motion in a sea way.
The equation favors heavy boats with lots of overhang and a narrow beam. These are all factors that slow down a boats response in violent conditions, which is a major factor in reducing crew fatigue. A value of 30 - 40 is recommended for a cruising boat. Racing designs are typically less than 30, and a full keel, Colin Archer design, could be as high as 55. Ted's recommendations were used for the optimal values, with a minimum of 25 and a maximum of 50.