The answer is more complicated than just wind
speed. Wave conditions, mast
steps and gusts (and a whole host of other variables) also play a large role. But a simple equation can be derived by multiplying the weight of the multihull
by 1/2 the beam to derive the maximum righting moment (ft/lbs) at 10 degrees. The sails
has a certain overturning power which is calculated by the area of the sail (sq.ft.) multiplied by the height of the center of effort (ft) which gives the moment of area of the sail (cubic ft). Then add the moment of area of all the sails
at a given sail set and mast and hull moment of area to give the total moment of area. At 20 mph wind
the maximum pressure of the wind is 1.22 lb/sq.ft. The maximum wind pressure of 100 mph wind is 30lb/sq.ft. You can then create a graph to show the maximum righting moment by putting wind speed on the x -axis and the moment of the sail area and hull and mast on the y-axis. Since the mast and the hull will remain the same you can remove these numbers from your graph to give the moment of sail area (cubic feet) for any given wind condition. If you stay under that moment you theorectically will not capsize
Thus if your boat weighs 10,000lbs and is 20 feet of beam: the righting moment is 100,000ft/lbs. The maximum moment of sail area that can be carried in a 20 mph wind is 100,000 divided by 1.22 or 81,967 cubic feet.
Then do the same for 100mph and drawa line between the two values.
A chart can be created showing the possible sail combinations that would provide the maximum moment of sail area for each sail set combination. Thus you can sail in confidence that theorectically you will not capsize
. Do not forget to consider that wind speed at the deck
is lower than at the moment for the sails and it is suggested that you add about 13% to the highest wind gusts.
Please note that I claim no accuracy for these calculations and each person should do their own homework (liability statement :-) but they are based on some fine research
by Charles Dennis and Hugo Myers Ph. D.