Mmmm, tricky one. Bethwaites High Performance Sailing and its sucessor are good books without any doubt but they are not per-se design books. Well worth reading though. In High Performance Sailing, I have a few issues with subsequent developments in lower or medium power hull shapes that Bethwaite ignores, because of the age of the book and the fact he had moved onto fast skiffs. The skiffs have problems of their own in terms of nosediving so you need to be very careful in the aft volume distribution and forward lifting sections to resolve this. Less static than 'dynamic' problem, check out both the RS100 (Paul Hobson) and the Devoti D1 for newer skiff types that are not quite as badly behaved for nosediving. Note the problem is not eliminated (probably impossible) but it is easier to handle. Primarily the problem is the lever from the force (on a gust) at the topmast forward pushing the bow down. All boats get this but if you cannot move aft or sink the stern sections by moving your weight aft? how does it react - pitchpole.
So there are a few choices, he (FB) is pretty much correct in the Sail Carrying Power ratio of 30%. Which side of that do you want to go? An 11' International Moth is pretty much cutting edge stuff. If I was to try a design of one of these I'd definitely sail a few first. I'd also expect to build 5 or 6 different foil sets to get it to work somewhere near max. If you are below that 30% it is a bit easier but you will still find there are quite a few new tricks since his book was written. Also worth googling the PlusPlus at 14' that fell too much in between the two sides of the ratio and is interesting, in just that. Check Keith Callaghan's Hadron as even a scaled down version would actually work pretty well. Depends on what you want and the waters you expect to sail on.
If you are going to design a boat, that's fine but check where the loadings go. If you understand these well, then you should be able to resolve things to come up with a design.
