From an earlier post on another forum:
Just did a very rough but accurate couple of sketches illustrating what happens with and without foils on a tri that can fly the main hull with or without foils:
1) top sketch shows main hull just clearing water and ama foil deployed.
Righting Arm(RA) is 7.71', angle of heel is 16 degrees.(slightly less RM)
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2) bottom sketch shows main hull just clearing the water and ama foil retracted.
Righting arm is 8.25', angle of heel is 19 degrees.(slightly more RM)
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With a trimaran that can fly the main hull with or without lifting foils, these rough but accurate sketches illustrate the following:
a-- the take-off angle of the foil equipped boat is less,
b-- the wetted surface of the foil equipped boat is less,
c-- the Righting Arm, and therefore the Righting Moment of the foil equipped boat is less than that of the boat with no foils.
d-- The portion of the ama hull available for pitch control is greater on the foil equipped boat, which, along with foil placement, will reduce the potential for pitchpole.
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The same princible is apparent on boats like the NACRA 20 which has
less RM than a cat with the same beam w/o curved lifting foils.....
Both sketches show the main hull at the same height above water ,just at takeoff....