Hi Steve,
Relative to your question about the top speed of the big cats: The most important design characteristic of these around the world racing catamarans is safety at speed. This means that these boats have to have the capability of sailing at speeds of 35 or 40 knots with adequate safety margin. At high speeds how does a catamaran get in trouble? It pitchpoles! What makes a catamaran pitchpole at high speed? Ans. A rapidly rising hull drag characteristic. How do you delay this rapidly rising hull drag characteristic. Ans. Make the boat loooooong! Then the theoretical max boat speed is well beyond the speeds the boat will see in actual use and the probability of pitchpole is greatly reduced. Also the pitchpole resistance or restoring moment of the hull is significantly increased with longer hulls. It is a conservative approach to a situation where peoples lives could be in danger and it greatly increases thr probability of success of the whole effort.
Fineness Ratio: Hull fineness ratio is simply LWL divided by max hull width at the waterline. The equation in many books for the hull speed limit of a displacement hull is:
Vel max = 1.4 X sqrtLWL. This equation seems to work for keelboat monohulls that have a hull fineness ratio of around 4:1 or so. In this form it sure doesn't work for beach cats. What I have found is that for displacement hulls the 1.4 coefficient varies with hull fineness ratio. For beach cats this coefficient varies between 4 and 5 depending on hull design. This says that a 20ft Tornado will have a max top speed of ( Vmax = 5 X 20**.5) or
22 knots. This relationship has served me well in analytical studies.
As far as the width of the M20 goes, the 9.5 or 9.7ft width is correct. It is disassembled to trailer. The boat has a 34ft tall mast and all the sail area in the mainsail so the center of effort is much higher than in the Tornado sail plan. The boat is 130 pounds lighter than a Tornado so the platform righting moment is well down from the Tornado, like 40% less. Add to this that the M20 crew lever arm is shorter than the Tornado and one can quickly come to the realization that the the M20 system is much overpowered (overturning moment/righting moment ratio) relative to the Tornado. If the boat had more righting moment, the crew could drive the sails harder and develope more sail thrust and make the boat go faster. It is that simple, f = ma.
Wind Force and Wind Power:
Wind force is a function of velocity**2 and has the units of pounds force.
Wind power is wind force times velocity and has the units of ftlbs per second. Wind power is a vel**3 function.
Sometimes people use these terms interchangeably but in the context of what they are saying you can usually understand what they mean.
Bill