For an efficient displacement hull 30 % more drive (thrust) is needed. With the higher speed this means that 52 % higher energy input (=more horsepower) is needed. For a sailcraft this also means major improvements in the rig efficiency as the rig needs to harvest 52 % more energy from the same conditions BEFORE it can be translated into higher speed. A significant portion of the initial energy harvesting goes into kinetic energy of the craft; ergo into accellerating the craft to a high speed. This is why Macquarie Innovation needs a long track where it can pick up speed before it enters the measurement track of 500 meters.
Wouter
That mix of units is giving me a headache. <img src="http://www.catsailor.com/forums/images/graemlins/confused.gif" alt="" />
power <> energy <> unitless efficiency
and
kinetic energy <> acceleration
Drag goes with velocity squared, so...
That is a conservative approach.
For displacement hulls a power factor of 2.5 is more appropriete.
Wouter
Except that at 30+ knots, a 40ft boat is well beyond displacement mode. I know, I know, a long, slender sailing cat hull "planes" differently than a short, wide power hull, but no way can it be considered displacement.
