First of all; Boards were designed for the I-18 and it could well be that the I-20 puts more load on the boards. On the other hand I believe that this is not the case for the overall width of the boat is equal to the I-18 and therefor they are both equally limited in righting moment and thus in maximum sailforce. That unless you sail the boats 3-up which is sometimes done in heavy air here. (Not in races though !)
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<br>I think they did it for the same reason as you did it, they've must have felt the tripping effect and I also believe that long boards are not needed at high speeds and only create more drag.
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<br>Visulize it like this. An aircraft wing (foil) has one optimal set of working conditions when it is not fitted with extras like flaps and slats. Going slower means not having enough lift from the wing so the angle of attack needs to be increased drasticall = drag. At higher speeds the wing produces to much lift, so angle of attacked must be decreased making the ratio lift /drag a bad one. On wings they use flaps and sorts to alter the lift characteristics of the wing and adjust it to different speeds. You can 't do that with boards. You can however change the total surface area by pulling the boards up or pushing them down.
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<br>In effect what your doing is adjusting the surface area in such a way that the optimal angle of attack is needed in order to get the lift you need. A board at a optimal angle of attack will nearly always produce the smallest overall drag.
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<br>Ofcourse the lift characteristic is dependend on velocity squared so there are big differences to be found at even small speed differences.
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<br>I'm still working out of more accurate model of the boards but I assume that this goes some way in explaining why they reduce board area in higher winds.
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<br>BTW, most sailors assume that more board in the water is always better. This is understandable but errornous. Lift and drag characteristics are similr to parabolic graphs they have an optimal workingpoint and drop of on both sides. Adjusting the boards is a must. Often asked question why don't the Tornado guys do it ? THis is because they have centrebaords and an centreboard that is partly "pulled" up leaves a gap in casing and this is more draggier than leaving the boards down.
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<br>Pulling boards up or fitting smaller boards in common in dinghy and skiff classes.
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<br>Wouter
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