I didn't say :"lighter weight boats are a technical breakthrough for beach cats"

And how does "Prepreg construction and the autoclave were used to make spaceship parts and airplane parts and race car parts long before they were used to make beach cat parts" conflict with my statement of "simply because the technics either didn't exist back then or were still far to expensive to be used in anything other than space flight."

The fact that they can be applied now in cat design is progress and advancement.

You keep yepping on about breakthroughs, I didn't as I wrote "They may have been spread out over a longer period of time and therefor can't be really described as breakthroughs but a modern cat is certainly not more of the same old 80's technology"

Then you throw in "The use of prepreg materials and the autoclave in beach cat construction is not an invention" after I called te use of this in cat design an INNOVATION. There is a big difference between invention and innovation, Bill.

And as for "Square top mainsails: Nothing new! If you look in an aerodynamics text book" Both Arvel and Bethwaite have completely debunked the use of aircraft earodynamics to sails. It turns out that soft cloth sails behave totally different from aircraft wings and squaretops are used for different reasons than tip vortexes. And if you really want to now any aerodynamics book will name and eliptical wingtip as the perferred wingdesign when looking at vortexes alone.

This use of aircraft aerodynamics is so 80's, since the beginning of the 90's most advances in catamaran saildesign has come from low speed model gliders competition and the (renewed) study of pre- and underpowered flight experiments. These experiments focus on the seperation bubbles and reattachment zones that are simply NOT found in powered fixed wing airraft studies.

"On the ARC boats you and others have missed the whole point" Did I ? As far as I know ARC boats have not opted for the "expensive low weight tornado" route and just stacked up more sailarea and increased width and are still more expensive than common production boats like the I-20 which, as you know, gives the Tornado a good hurry up around the course. Clearly there are other things at play here too. Besides which boat do you want to trailor behind your care a 12 foot wide one or an 8 foot one ?

And "To be faster than other boats a superior design must have a higher righting moment to sail area ratio also. Without this parameter being superior to other designs, the higher sail area to weight ratio cannot be taken advantage of" is just nonsense Bill. Answer this to me.

What happens when for a given design the ratio between righting moment to sail area DECREASES LESS than the ratio for weight to overall sail area ?

Yes power is decrease by virtue of the first ration but when drag decreases even more than the given design will become faster.

How else can modern A-cats be faster than those of 10 years ago when they had shorter mast and about 25 kg's heavier platform ?

How else can a Taipan 4.9 outperform a H16 IN ALL CONDITIONS when afterall the H16 total sailarea is actually slightly more than that of the Taipan and both are of equal width ? And the Taipan has a taller mast at that. According to your reasoning the Taipan should be held back by her rig that has a worse ratio of righting to sail are than the H16.

I know why the tornado has a 10 ft wide beam and I also know that it is possible to design a faster craft WITHOUT :"a higher sail area to weight ratio and a higher righting moment to sail area ratio!!!"

Eventually it all comes down to improving the power to drag ratio and a designer can ALSO do that by making sure that the ratio of righting moment to sail area reduced less rapidly than the ratio for weight to sail area. And the logical way to do this is to reduce platform weight. Platform weight hardly contributes to the righting moment but does fully contribute to drag.

Example

-1- 150 kg crew on a 2,5 mtr, wide 150 kg's platform weights 300 kg overall and has a righting moment of 150 * 2,5 *0,5 + 150 * (2,5 + 1) = 187,5 + 525 = 712,5 where the distribution is 26 % to 74 %

-2- 150 kg crew on a 2,5 mtr, wide 100 kg's platform weights 250 kg overall and has a righting moment of 100 * 2,5 *0,5 + 150 * (2,5 + 1) = 125 + 525 = 650 where the distribution is 19 % to 81 % %


Boat two has 91 % of the righting moment of boat 2 and can therefor only carry 91 % of the sailarea with only 91 % of the power BUT is also has only 83 % of the weight of boat 1 which is directly translated in reduced drag of alot more than the 9 % of the power reduction. Ergo reduction in power coincides with an even bigger reduction in drag and thus higher speeds are achieved.

There is the counterexample of your "Nobody is going to build a boat faster than the .... (fill any boat that you want) until it has a higher sail area to weight ratio and a higher righting moment to sail area ratio!!!" statement.


Simple not ?

And how does your own statement of "It wasn't until the late 1980s that spinnakers began to work to advantage on the RC boats and that was after the purchase of several spinnakers from several different sailmakers" mix with your earlier statement of "That is not improved boat design. Spinnakers have been added. Spinnakers have been around for 50 to 75 years or more. That is nothing new"

Going by your own statements of your latest post something DID change between your first own experiments with spi in 1983 that failed to produce results and your retries of the late 80's and early 90's. Now I can tell you a whole lot changed between the early 90's worrell like spi's and the newer generation high aspect spi's of late 90 early naughties.

Now I DO share your skeptisme with respect to certain "improved designs" and indeed it is more difficult to design a faster boat than one thinks. Most designers do it wrong. As like with the M20, there the designer reduced overall weight, increased righting moment by having a much taller mast AND decreased the width from 10 to 8,5 ft. at the same time. Mastrom shouldn't have done all three things at the same time. You can do two of these and expect to have at least the same performance or better but doing the third pretty assures that you will do worse under certain conditions.

But I stand with my counter argument to your first post. There has been significant innovation and improvements in catamaran design over the last 20 years and as a result the boats have become faster. Due to the gradual improvements I don't think "breakthroughs" is the right describtion for the advancements. This does not mean however that we're witnessing more of the same 80's stuff.

it is either this or accepting that the only true breakthroughs made in multihull design were made 3000 years ago by polynesian boat builders who discovered the advantages of form stabilized designs over weight stabilized designs and discovered the vastly superior performance of Crab sails in all conditions but pure upwind sailing. After that the introduction of bermuda rigs was only a specialization to race courses that featured a dominant upwind leg.

Because in all honesty what did change since then. We still have have two floater connect together by beams, a mast with a sail made of cloth, a peice of rope to trim the sail and a rudder that is hanging from the stern to steer with.

Regards,

Wouter