The equation favors heavy boats with some overhang and a narrow beam. These are all factors that slow down the boat's response in violent waves. A value of 30 - 40 would be an average cruiser. Racing designs can be less than 20, and a full keel, Colin Archer design, could be as high as 60. Our template value of 36 indicates that comfort is a high priority on cruisers.
Large values resist rolling forces.
A heavy rig can greatly increase I, with little impact on displacement. The roll period is based on the moment of inertia. Simply stated, a sailboat's roll period, in seconds, is inversely proportional to its stability. Unstable boats have long periods, stable boats have short periods. Then count the number of full cycles in one minute, and divide into 60.