Hello Alutz,
I think you have calculated the numbers correctly but the equation you have shown is not correct.
The correct equation is: RiMo=Bwt X Bwd/2 + Crwt(Bwd + 1m) This equation will give the numbers, RiMo, you have calculated.
Don't worry about being able to fly a hull. It will happen! The dynamic pressure of the wind varies with wind speed squared, velocity**2. You are considering increasing the righting moment to sail area ratio on the F18ht from 30 to 34 or a 13.3% increase. When the wind speed is up by 6.5%, the wide boat has the same ratio of righting moment to overturning moment as the narrow boat. A 6.5% increase in wind speed at 12 knots is 0.78 knots or a little less than 13 knots total windspeed. This will make a big difference in boat speed as soon as you need to get out on the wing. The narrow boat will be luffing/feathering sail area when the wide boat can drive all of his sail area. Sailing to windward on the narrow boat, the drag from the luffing/feathering sail area will be subtracting from the forward force the sail is generating which is already compromised because the narrow boat cannot hold the boat down. The narrow boat takes a double hit. He cannot drive 100% of his sail area and the sail area that cannot be driven is producing drag. This drag is subtracting from the reduced sail force the narrow boat has to operate with in the first place because he cannot hold the boat down.
Go fast and watch those bows. Stand aft on the boat when necessary. You are putting a supercharger on your boat so be ready for more horsepower and speed.
Bill