72 One-Design Class Sailboat Handbook 



standard, and by giving a penalty or increase in waterline length when 

 displacement is less than a standard. 



Similarly, beam affects the speed of a boat. As a general rule, an increase 

 in beam increases wave-making resistance, and it also increases wetted 

 surface, thus increasing skin-friction resistance. However, as explained 

 below, it must be realized that if a boat has insufficient beam it cannot 

 properly carry her sail and therefore will suffer when on the wind. The 

 formula provides for a decrease in the waterline length for increased 

 beam above a standard, or for an increase in the waterline length for 

 decreased beam below a standard. 



Also, the draft of a boat has a considerable effect on speed. A boat with 

 light draft may benefit by having less wetted surface, whereas deep draft 

 lowers the center of gravity, thus adding to stability and sail-carrying 

 capacity, as well as perhaps giving a more effective lateral plane, or better 

 performance to windward. 



Although corrections for these factors, plus corrections for freeboard, 

 propellertype and location, centerboards and iron versus lead keels are 

 important and necessary; they are direct calculations by themselves as to 

 their effect on speed and on rating. 



However, stability is a very important factor in determining the sailing 

 qualities of a boat, as it involves the combined effect of many of the other 

 factors. It is therefore necessary to devise a formula to take stability into 

 consideration in order that variations in it may be properly evaluated. 

 This results in some of the more complicated calculations of the measure- 

 ment rule for translating stability into the effect on speed and rating. 

 Ballast-to-displacement ratios and measured beam-to-beam ratios are 

 needed from which is derived a correction factor to rating. For instance, 

 more ballast or more beam increases the stability of a boat and results 

 in a penalty correction to rating, but the corresponding increase in dis- 

 placement or beam derived by their respective formulas increases the 

 resistance of the hull through the water, and results in a credit correction 

 to the rating; so that a loss in one adjustment may be offset to some 

 extent by a gain in another. 



Therefore, in the final calculation of the rating, the plus-and-minus 

 corrections for all the factors are summed up and applied in the rating 

 formula to determine the rated length of the boat. 



