An unlimited beam width for a catamaran is fine BUT, the wider the hulls are apart, (assuming the fore and aft position of the mast step position is kept the same), the more prone the cat is to pitch poling due to the increased sail dynamicly generated down ward pressures transfered to the bows. In fact, rather than achieving a more stable base by widening the distance between the hulls, the reverse is always the outcome when the ideal ratio between hull beam, hull waterline length, mast hieght, sail area, and aspect ratio of sails, is exceeded. A very rough "laymans" measurement for this is approx 14' length, 7' beam, upto 25'6" mast hieght, and an approximate sail area of 130 sq ft (depending on the aspect ratio, the lower the aspect ratio the larger the controlable -with advantage- sail area that can be carried. The use of a spinnaker falls outside these dimensions as all sorts of dynamic changes occur to the controlability of the boat with the kite, all of which are able to be comfortably incorporated on the same cat.