Does any one know what the lifting difference is between a banana board, an angled straight board and a straight board in the vertical line with the boat. Calculated in theory
The diffference between a 6 degrees outward canted symmetrical board (hyped up development of yesteryear) compared to an 6 degrees inward canted symmetrical board when the luff board is fully lifted is 30 kg on a doublehanded F16 with crew on trapeze = (20% of the total saildrive perpendicular to the centreline of the boat.)
The A-class has less righting moment and less saildrive byt the ratio of 20% will still hold. Roughly speaking 15 kg lift on the A in the same situation with the crew trapping.
When allowing boards to go to 15 degrees inward angle the difference becomes 50% of the total saildrive perpendicular to the centreline of boat (= 75 kg on 2-up F16 and 37 kg on A)
Calculating the difference between these boards and the banana boards is not easy to do without agreeing on the specs of the banana board first. For all I know the bananaboard can be twisted towards its tips, making it a symmetical daggerboard near the hull and an permanently positively angled lifting foil at its tips. I will need to know the cord and radius of arc of the banana board and the amount of twist or fore-aft angle in its (hull) slot (= gives incidence angle)
Basically a 0.16 sq. mtr daggerboard with a 0.20 mtr cord (aspect ratio = 4) can rather efficiently
create 75 kg force perpendicular to its plane. It can produce even more force by then the lift drag ratio will be less attractive. So if the daggerboard is L-shaped then a horizontal tip of 0.20 by 0.20 can produce 25% force. Of course we have ignored some efficiency effects here but such a L-shape form can be used as a good first approximation of the curve banaboards which tip reaches 0.20 mtr seperation relative to the centreline of the part in the daggerboard well (assuming this one is on the vertical).
It seems to new A-cat anti foiling rule allows up to 0.30 mtr seperation between the vertical and the tip of the banana board = approx 38% of saildrive transformed into vertical lift (= effective weight reduction craft)
It is not hard to calculate these things using theory; it is just that there are so many factors that need to be fixed/chosen for a value can be produced.
Wouter
