With a plate that is vertical (in plane) of the hull; the leeward hull (roughly) pivots around a point at the bottom of the hull.
The boat will now be heeling / moving about a point down the plate (not at the leeward hull); as the hull is lifting; thus the pivot point moves inboard a foot or so (depending on the plate profile) and thus a wider boat is required for the same sail plan.
Spent a while discussing with Tornado_Alive as I was wondering why the F20 was so wide; it’s because the curved boards reduce the effective beam of the boat.
Totally agree with what you are saying about normal vertical boards but with curved boards its a lot more complex. As soon as the boat starts moving through the water, and thats what we try to do ( some more successfully than others ) all sorts of other " vectors " start happening.
Its very new technology with a long long way to go before we fully understand the benefits and repercussions of various assymetrical or symmetrical curved boards but we need to be thinking ahead a little perhaps and think along the lines of at least fitting the newer styles of adjustable daggerboard cases where we can fit curved or straight boards.
See you at the 3 Piers for a beer to discuss.
