214 One-Design Class Sailboaf Handbook 



a catamaran? First, its twin-hulls give it virtually the speed of two boats 

 with not much more wetted surface area than one. Since resistance at 

 high speeds is primarily a matter of wave formation, the narrower the 

 hulls and the straighter the run, the faster you'll go. For water doesn't 

 like to be pushed apart, or bent. Comparisons of narrowness (potential 

 speed) are easily made by relating a hull's waterline beam to its waterline 

 length. A beam that's one-twelfth of length gives good performance. A 

 beam that's one-thirteenth of length would be even faster, while a water- 

 line beam one-eighth of length would be noticeably slow for a catamaran. 



With regard to having a straight run, you want the water to be bent 

 as little as possible aft of amidships, not only along the keel but also at 

 water level. Hence the desirability of transom sterns of approximately 

 full beam. Other considerations contributing to high-speed performance 

 are: 1. The sharpness of the entry at each bow; 2. Sufficient distance be- 

 tween the hulls to minimize interference between the bow waves; 3. Suf- 

 ficient vertical clearance between the water and the underside of the cock- 

 pit to prevent "belly drag"; 4. and last, but not least, the matter of total 

 weight aboard— for surprisingly light weight helps at high speeds much 

 more than in light air. Among monohull sailboats, the bigger they are the 

 faster they go, and the smaller they are the slower they go (see page 000). 

 Likewise with catamarans— but even more so. For, as you cut down on 

 overall length, you soon come to a size that ceases to benefit from being a 

 catamaran. The joker here, of course, is that you and your crew weigh 

 just as much aboard the little catamaran. Hence, to support your weight, 

 the beam of each hull of the small cat must be relatively much fatter than 

 one-twelfth of its length. So you no longer have truly narrow hulls with 

 sharp entries. Furthermore, whatever surface waves there are will bother 

 any small cat out of all proportion to its slightly smaller size, and espe- 

 cially with regard to the way a small cat "hobby horses" while going to 

 windward. 



Good performance in light air is achieved by: 1. reducing underwater 

 resistance; and 2. increasing sail-power. Underwater resistance at slow 

 speeds is primarily a matter of the number of square inches of "wetted 

 area." Since the least amount of wetted area for a given displacement is 

 in the shape of a hemisphere, it follows that the least amount of wetted 

 area for a catamaran will be obtained if: 1 . the underwater cross section of 



