A good rule of thumb for righting moment is :

Righting moment RM = 0.5 * boat width * boat weight + (boat width + 1) * crew weight

The formula uses SI units, so meters and kilograms, if you want to do it with feet and pounds then replace (boat width +1) by (boat width + 3) (this a rough approximation)


The results are :

F16 sloop two-up with 150 kg crew

RM = 0.5 * 2.5 * 107 + (2.5 + 1) * 150 kg = 133.75 + 525 = 658,75 = say 659 kgm



F16 sloop two-up with 150 kg crew and 1 foot wings (=0.3 mtr by 5 kg each)

RM = 0.5 * 2.5 * 117 + (2.5 + 1.3) * 150 kg = 146.25 + 570 = 716,25 = say 716 kgm = 8.6 % more than standard F16

Is comparable in righting moment to putting a 166 kg crew on the wire of a wingless F16

RM = 0.5 * 2.5 * 107 + (2.5 + 1) * 166kg = 133.75 + 582.5 = 716,25 = say 716 kgm = 8.6 % more than standard F16



F16 uni one-up with 80 kg crew

RM = 0.5 * 2.5 * 104 + (2.5 + 1) * 80 kg = 130 + 280 = 410 = 37 % Less than standard sloop 2-up F16


F16 uni one-up with 80 kg crew and 1 foot wings (0.3 kg by 5 kg each)

RM = 0.5 * 2.5 * 114 + (2.5 + 1.3) * 80 kg = 142.5 + 304 = 446.5 = say 447 kgm = 32 % Less than standard sloop 2-up F16 and 9 % more than standard 1-up.


Don't make out too much aof 10 % higher rigting moments in the way of performance enhancements.

A good rule of thumb giving the UPPER limit to windward leeward gains is :

0.5 * (Sq.rt (new sail drive) - 1)

so

0.5 * (Sq.rt (110%) - 1) = 0.5 * (sq.rt (1.1) - 1) = 2.4 % or about 90 seconds per hour when doing everything else just right.

This is an upper boundery as increases in overall weight, windage and the fact that the relationship is "stronger" than a sq.rt take away from the gains.

Typically I use a power relationship of 1/2.5 instead of of the normal sq.rt that is a powerrelationship of only 1/2

So

0.5 * (110%)^(1/2.5) - 1) = 0.5 (1.1)^(1/2.5) - 1) = 1.9 % = 70 seconds per hour bouy racing when doing everything else just right.

This number I would use as a relatively accuracte estimations of the performance gain IN HIGH WINDS only ! Of course in all conditions where normal trapping of sitting on the luff hull is sufficient the winged catamaran will have no advantage at all, rather it is expected to be disadvantaged.

Wouter