Bill,

>>Scaling hull weights by length to the third power is standard naval architectural practice. It is not something I came up with.

So is using Froude law for max hull speed but we all know that that is pretty meaningless when looking at catamarans.


>>The RC30 hull weight of 175 pounds is a carbon hull. The three beams on the RC30 are aluminum. There are also other parts to consider like ropes and pulleys and wires and spimmaker poles and boards and rudders, etc. All up with sails the boat does weigh 900 pounds. Oh, that includes an outboard motor bracket too.

Okay so I've I shrink that 30 ft platform without any changes to an 18 foot platform using the 3rd order theorema than teh 18 foot platform would only weight (18/30)^3 * 900 = 0,216 * 900 = 194 lbs = 88 kg's and that is including weight saving thingies like motor brackets and a third beams. And this 18 footer is still a double hander with jib and spi.

Doesn't this strike you as being a bit odd ? Could is be that the 3rd order rule of thumb is being misapplied here ?

Sure the 3rd order is very neat when looking at cargo ships that are limited in their overall weight (dominate by the weight of their cargo) by how much displacement (volume) they have but sports catamarans aren't cargo ships. Sport catamaran platform weight is mainly determined by strengh and stiffeness considerations.

I'm only saying that the 3rd order rule of thumb can't be applied to catamarans.


>>If you were the builder, which way would you go?

I may go your way if I was designing a fast cruising boat and my own way when designing a fast regatta boat.

I would just as luiz wrote, Go lighter, more sailarea and wider simulatiously when I could and go lighter and less sailarea when my width and length was limited.

I will never go heavier. Nor will I ever reduce width unless I'm forced to. When limited in width I will go as light as possible and adjust my rig and area to accordingly.


>>The RC27/30 concept is not maxed-out by a long shot. All that is needed in more money.

Which is exactly the direction in which we don't want to go.

>>Wouter, you speak loudly for someone who has never put a boat into production and has no record or facts to stand on. You speak out without knowing all the facts. I find that distasteful.


You sound like my old professor Bill, (and I cornered three of them in my time) he too had convinced himself that new discoveries and advancements were made by people other than young ambitious persons with no track records.

If only the Wright brothers listened to wise old men, if only Einstein had kept his weird fantasies for himself and had stuck to conventional wisdoms like 19th century contemporary physics like everybody else.

I'm not disrespecting you here Bill, I'm really not. But the fact that your 30 years ahead in life and have produced a series of boats in that time doesn't say anything about who is right and who is wrong. Mathematics and Physics don't work in that way.

So we come back at the A-cat example.

Answer please how an modern A-cat is faster than an A-cat of 10 years ago when it now has the same width, the same sailarea, a taller mast and a much lighter platform.

This example alone defies your statements. According to you is should be slower because it now has less righting moment per sailarea than before and her width was not increased when than the mast was made taller. How can it still be faster ?

Their is only one modification left that must have been more than enough to offset these negative effects and to such an extend that enough is left to make the whole setup faster and that is ....

Wouter