Hello Rick,
There is one very important difference in hull design between a one person and a two person boat. The hull height and displacement have to be designed for the weight of two people if the boat is going to work well as a two person boat. The A class cat is highly tailored as a one person boat. With one person on the wire and flying a hull, the cross beams intersect the leeward hull just a few inches above the inboard sailing waterline. If you put two persons on this boat and put all the weight of the boat and sailors on one hull, the front beam will be dragging in the waves of the chop that go with this wind strength and point of sailing. So you can't just put two persons on a boat designed for one person and have a good sailing boat. With two on the wire the sail thrust is approximately doubled; lookout for pitchpole, lookout for broken daggerboards, lookout for broken mast, need more mainsheet mechanical advantage, lookout blown out sail! You can take a two person boat design and sail it single handed but a one person design sailed by two persons, that doesn't work very well.
Bill