I like it, but it could use some nice, cushy padding. I can see some advantage, too, on the starting line, if you slid the thing out to leeward.

Mary,

Your post reminds me of this crazy guy who had this nervous disorder about his boat getting hit on the line. Not altogether unreasonable with me out there but what was funny is that he'd have this huge telescoping pole that he'd switch back and forth to leward while racing. It annoyed the hell outta us, but he wouldn't remove it despite our promises that we wouldn't get near his boat. He finally was forced to get rid of it halfway through the day when he poked it through someone's sail

Wouter,
Scaling hull weights by length to the third power is standard naval architectural practice. It is not something I came up with.
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. Yes, the other parts of the boat do weigh more than they could but they are not made of carbon. If everything else was made of carbon as the hulls are, one could reduce the weight of the boat by at least another 100 pounds and 'double the price'. If you were the builder, which way would you go? More of these boats are used for recreation than racing. Some of them are even built with fiberglass hulls. The RC27/30 concept is not maxed-out by a long shot. All that is needed in more money.
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.
Bill
Bill

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

Could this be related to volume changes with the third power?

Hi All

Some of the early B-Class development cat designs had sliding seats ,-read Reg Whites books -in U K -on early C-and B class development--time frame 60s -70s ,-
PROBLEMS ARE WEIGHT -complexity and stationary for -aft location .-

One of the most interseting versions of that were on the later 80s Worrell designs in the open class -
One had a 10 ft fold up rack mounted on the outside edge of each hull on a traveler ,-
It looked a little like someone had gone wild with an erector set and put it on a Harken traveler .
--but ,-simple math is ,-put a 200 lb crew 10 ft out further 200* 10 -thats 2000 extra ft lbs of righting moment holding the sail forces ---talk about more beam !!

Another version of 10 ft fold up rack just used an alum. pole and mesh seat at the end --kind of reminded me of a giant fly swatter in appearance --
Both were very effective and fast -

Seems most everything has been attempted in one form or another ,-its refining those ideas and concepts into working form sometimes requiring connections of other ideas and invention that eventually makes them viable .--its fun stuff,-but expensive and time consuming ,-and not alaws marketable .
There are some great books on curious yachting inventions thru-out history ,-and room for more -one on cat design or multihulls would be very marketable today !!
Patten searches are a great source ,and fasinating looking at old diagrams dating as far back in the U S as the early 1800s -
Recall the ill fated giant multihull round the world racer with two masts ,-one on each hull ,-as the tri foiler has ,-You can find this pattened as applied to a square rigged ship in the early 1800 for example -many many more
The same ideas brought back in modern form and refined again and again .-eventually they work !!

Wouter,
I have never mentioned the CFR20 or M20 before on this or any forum before. One thing I am trying to point out is that boat performance can be calculated long before the boat is ever built. That's what engineers do. You seem pretty keen on these ratios now. This is the first time I have heard you mention them. The approach that I take to design a faster boat, higher sail area to weight ratio and higher righting moment to sail area ratio, does work for higher performance boats and it is the 'low cost way' to get there. This super light weight boat with all carbon parts approach is another way to get there but it is the high cost road. For example: Let's imagine a 20ft boat built in an autoclave that is made out of materials far superior to the Tornado such that another 100 pounds is removed from the boat weight. Lets's assume that the new boat has the ratios such that it is much faster than the Tornado. This new boat built out of these super materials and super construction methods will cost much more to build than a Tornado. When this new boat costs 1.5 to 2 times as much as a Tornado, how many of these new boats are you going to sell?
Here's another ratio for you, Wouter. If the pitching moment to restoring moment ratio had been calculated for Playstation when it was only on paper, the boat would have been 125ft long in the first place.
Bill

How about modified/taller elevator shoes from the '80s era?
Might be awkward getting around the tramp or beach?
Therefore, lower leg extentions could fold/pop off the lower legs.
Stilts anyone? With velcro toerails?

Or maybe heavier heads. How about wearing helmets made of lead?

I like that idea! (Although some of us have probably been accused of having fat heads to begin with. )

Yes, that is why the displacement of Bills 18 foot imaginairy hulls is so small.

Wouter

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

That's great to hear...I am glad Tom picked the SC17 to revive...Has to be the best "boardless" beach cat ever designed in the 16'-17' range...Faster, Stronger, Stiffer, Better Balanced, Points Better, Easier to Tack, Near imposible to pitch pole. All the fun of the other 16'-17' "beach" cats, with none of their inherent problems.

The SC17 made sailing fast fun, instead of work. Marketing, not the designs themselves, have (IMHO) always been the Achilles heel of the Super Cat Series. I wonder what would have happened if Hobie Cat (instead of Boston Whaler, which seemed to withdraw from the market prematurely) would have bought the designs from Bill when they were first introduced? With their beach oriented marketing machine behind his designs the SC17 might have been able to find it's true potential in the market place. The outcome of that scenario will never be known.

It is my wish that Tom has great success with the up and comming ARC 17...hope he puts some photos on his web site...don't make it a covert operation...LOL... might stur up some interest if you did a little picture story on the development of the "new ARC" from the "old SC17" Can't wait to see it...

Wouter,
Here's an example of what I am talking about,"you frequently go off half **** and don't know all the facts".

>>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.<<

I didn't say the squaretop had anything to do with wingtip vorteces. What the squaretop sail/wingtip does is prevent spanwise flow down the low pressure side of the sail that originates from the sail top where the sail is narrow, where the leech is forward relative to the sail below. On a pin head sail or pointed wing tip the air exiting the sail/wing on the pressure side near the tip turns 90 degrees at the trailing edge and flows or is pulled spanwise down the sail to an area immediately below where the pressure is lower. Air wants to run downhill just like water. The air on the pressure side of the sail near the tip is at a higher pressure level than the air on the leeward side of the sail at say 50% chord a foot or so down from the narrow leech above. The pressure side air at the leech sail dives vertically down the sail, leeward side into an area of low pressure on the leeward side. This spoils the delta P across the sail at the top and reduces the span effectiveness of the sail or wing. The square top moves the leech aft and this delays the opportunity for the air exiting the windward side leech to flow spanwise down the sail to a low pressure area immediately below. With this spanwise flow diminished/eliminated, the span of the sail/wing is more EFFECTIVE, it more closely approaches the ideal lift for a given span. You could say the square top sail or square wing tip is an aerodynamic dam that prevents a parasitic spanwise flow which reduces the effectiveness of a sail or wing. It has nothing to do with tip vorteces.
Bill

Bill,
Is there any way that you (and all these other engineers) can put all this stuff into lay terms so the rest of us can understand it? As somebody already mentioned, it kind of excludes us normal people when you guys go into all this technical jargon.

I'll bet that if I understood what you were saying about vortices and spanwise flow, I could capsulize it in a sentence that people could understand. Unfortunately, I don't understand.

I have thoroughly enjoyed this discussion except the one comment excused by someone under the influence of the moon. It is good to see passion and mathematical data liberally posted without fear of the results often experienced on the other forum. To those of you intimidated by the formulas, read them anyway, or paste them into a file you can look at later. I have pretty good sized files from both of these fellows. One day you will see what they mean, and you will get there a lot faster if you do the work to understand them. Bill and Wouter are a lot smarter than most of us, but so was Aristotle. It is perfectly obvious that heavy objects fall faster than light objects and that the earth is the center of the universe....
Einstein said that the Creator was subtle, not malicious. I believe Wouter is trying to point out that subtle design changes with an eye on all the other aero/hydrodynamics can yield dramatic improvements. And indeed they have. Many of the things Wouter has discussed can be applied to your own 'dead boat' with encouraging results.
To Wouter: The specs I have seen and a witness say that the M20 is about 9.5' beam. What is your statement that it is 8.5' beam based on? If 8.5' beam for the M20 is an error, wouldn't that substantially change your analysis of the boat?
To Bill: (relax a little, this is as upset as I have seen you) When the big cats went for the run around the world in 2001, there was a thread (old forum) where you calculated that the over 100' boats had fineness ratios that should allow speeds of over 50kts. The fastest I saw anyone goes was about 35kts. In an earlier thread you had introduced this fineness ratio as a factor in the old LWL formula. When others inquired about the 'fineness formula', you gave no reply. Am I in serious error about the top speed of the megacats? Could you explain about the fineness ratio? Also, you recently stated that the power (force, KW, hp) in the wind varied as the square of the velocity of the wind. My old DOE manual for home windmills gives a formula for wind power that has a cube on the wind speed. And that is the understanding most my landsailing buddies have. Did I misunderstand your statement?

Sincerely, and best regards to both of you.

Boeing - US Government & Wouter
Northrop - Bill Robert

The time: WWII

Things were shaky in the world and the US was looking for a new longrange bomber....
Boeing can to the table with the B17
Northrop with (model # evades me at the moment) the Northrop Flying Wing.

** No disrespect to any ones fathers or friends that servered in B17s in WWII (friend of my fathers was a tail gunner and he made it home) **

Both Aircraft were tested by the Army and by Army pilots that had never flown a flying wing. The flying wing out performed the B17 in all areas except two:
1) It was going to be dificult to mount machine guns on the flying wing with the large flat wing surface.
2) The US government was in bed with the Boeing Corp.

The result is history "the flying fortress".... So what's the point... the better plane was not the popular choice. How many of the men we lost, could have come home if they were on the flying wing.

My last point: When Boeing received the bid, the Army was ordered by the Government to distroy all Northrop Flying Wings used in Testing. So they flew them to the dessert and gathered them alltogether (landing gear up) and drove large bulldozers over them to crust them. HA HA! they didn't crush, the Flying Wings supported the weight of the bulldozers and eventually had to be cut up (try to drive a bulldozer over a B17 and see what would happen. - FYI: the Bulldozer incident was never released for public knowledge.

??? O'yes, look at the new "State-of-the-Art" Aircraft today... FLYING WINGS!!

Show me an I20 or A-Cat in 20 years that looks as good as my SC20TR today, and I will eat my hat.

THE REAL ARGUMENT BILL... The numbers on the boats - it is killing them that they spent $12K+ on a "Go Fast" only to find that a 20 year old boat timed out over them.

I guess that would be me.

What I have been trying to say, in various ways, is that all of us regular people out here think that what you guys are discussing is probably very important, and we would like to know what you are talking about, but we need an interpreter. Nobody wants you guys to stop discussing and debating and arguing in your own language. But isn't there an engineer out there who can convert some of this into lay language so the rest of us can participate, or at least understand?

I could translate it. Thats technically what my job is... to relate technical information to people who aren't technical so they can understand it.

Its quite difficult actually.

I wouldn't know where to start though... Wouter crams a lot of jargon into his blogs :P

let's split it up - you take Wouter and I'll take Bill.

Thanks guys -- and it isn't even Mother's Day.