Hi Gareth,
Hull length is by far the most important hull dimension. I also point out that hulls, especially short ones don't scale. This F14 boat that we are talking about must support the same weight as an A cat for example. If you scaled an A cat hull down to 14ft, the length would scale down by 14/18 and the width would scale down by 14/18 and the depth would scale down by 14/18. All of the sudden we are looking at a scaled down hull that has 47% as much displacement as the A cat hull and it must support the same weight. That won't work.
So we have to do something like this: If the length of the boat is 14/18 as long as the A cat and it must support the same weight, then the hull width distribution must be 18/14 as wide as an A cat with a similiar keel rocker. Now we have a hull shape that will at least float on a reasonable water line. Now you see that we have gone way down in hull fineness ratio, shorter and fatter. But this is necessary in a short boat.
Bill