Join Date: Feb 2000
Location: Annapolis, Md
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One thing you need to realize is that the capsize screen ratio (or the motion comfort index) tells you absolutely nothing about how likely a boat is to capsize or how comfortable its motion is likely to be. I know that I have explained this on this forum before but here it is again, both of the capsize screen formula and motion comfort index formulas were developed at a time when boats were a lot more similar to each other than they are today. These formulas have limited utility in comparing boats that are very similar but are totally useless and misleading in most cases.
Neither formula contains almost any of the real factors that control motion comfort or stability. Neither formula contains such factors as the vertical center of gravity or buoyancy, neither contains weight or buoyancy distribution, and neither contains any data on dampening. In other words these formulas lack all of the major factors that actually control motion comfort or likelihood of capsize. Weight in and of itself has next to no bearing on motion comfort or stability; nor does max beam, which in this formula is measured at a single point on the deck.
An example that illustrates this might be two boats of equal length, equal max beam, and displacement, but one had a longer waterline and a 1000 lbs of lead in a deep draft keel, while the other had a shallow draft keel with a 1000 lbs less ballast, a hard turn of the bilge, and a 1000 lb heavier interior and deck.
Obviously the boat with the deeper draft, lower ballast and longer waterline would be the less likely to capsize and offer a slower motion through a smaller roll angle, yet their capsize ratio and motion comfort index would be identical.
That is why I see these formulas as being worse than useless.