Problem is that I fell for my own trap; dumb, dumb, dumb of me !
The example I gave of the B-class cat is wrong.
How could I be so stupid, I've been working on a comparable concept for years now. I should have known better.
The example I gave was :
"I would lengthen a nacra 5,7 hull and make the hulls out of carbon, use 18 sq. beams to make it 3,05 mtr. wide and put a 8,5 mtr. Taipan (4.9 or 5.7) wing mast with a large high aspect jib on it, optimize the sails for reaching, find a light crew"
First of all I one makes a platform alot lighter one must never lengthen the hulls at the same time. The first will reduce both wavemaking drag and wetted surface (friction) drag but the second will go a long wave in limiting the reduction of wetted surface drag again. Okay the wave making drag will be much more reduced by lengthening the hulls but that is only adcantagious when wave making drag is absolute terms is bigger than wetted surface drag at the topspeed. This is by no means certain, in fact it is likely that frictional drag accounts for a bigger portion of the platform drag than wave making does. So the design should aim on minimizing the frictional area to the max. This will only be done by making the craft lighter and maybe even shorter hulled.
Than the "making is wider to 3,05 mtr." Boy that was even more dumb to say. In the article of the C-class miss Nylex it was found that an earlier C-class named Quest 3 had beams that accounted for some 10 % of the total drag (incl rig and crew) and no less than 18 % of the platform drag. C-class cats are 14 foot wide = 4,27 mtr. This is a huge chunck of drag. What is the best way of reducing this darg component ?NOT HAVING (so much) BEAM, ofcourse. So from a efficiency point of view the best way to arrive at a low drag platform is to stay at 2.5 mtr wide and have less beam as well as smaller diameter beam = less frontal surface area.
Some fairing on the hulls before the beams will also do alot to minimized the drag that caused by water flowing over the decks.
But what about righting moment I can hear some think. Well the trick to high speed is having low drag. Not just alot of power. Beside my own ramblings on the webpage :
http://www.geocities.com/kustzeilen/heeling_pitchpole.htmlShow that a craft on a reach or shy broad reach (best course for topspeeds) is in far more danger of pitchploing than capsizing. So, the craft doesn't need more width at all. It will not be able to convert that width in power anyway because it will only pitchpoling more easily. In fact there maybe room the reduce width even a little bit to just over 2 mtr. (=O.5 mtr less = 1,5 ft less)
I would defiantely still put a wingmast on the craft as that has a better lift to drag ratio which is totally vital in achieving high performance.
I would still make the mast a little shorter to be able to get more thrust for a given pitchpole moment limit.
And I would still find a light crew.
So there you have it. Even I after looking and calculating at lightweight boats for so long fell for the predictable mistakes.
A laps of intelligence that I thought I should set straight. This boat will be a dog upwind even more but it certainly would go fast on reaches.
Wouter
