Listen up Darryl,
I ain't no backwater hick in this. Don't give me knife on its side examples. This is almost insulting. How does such a thing compare to any catamaran sailing in any way ? Come to think of it, the resistance that you still feel when the knife is held paralellel is caused by what ? Wavemaking drag or Wetted surface drag ? Now drag your little knife through honey, what happens ? Now pull your knife straight up from the honey, what resistance do you feel now ? How do the two compare ? Can this be explained by wavemaking drag as their ain't no waves in the second case ? It is the viscocity you say ! And exactly how is this different from wetted surface drag ?
Now I'm the first to accept another theory when my own is proven wrong or when a different approach is proven (more) right. But your approach up till now is :
"You use a lot of formulations gleaned from various places"
First of all you may call these places 'Technical University of Delft faculty Maritime Engineering' my dear friend. Cause that is where I 'gleaned' up some of these 'formulations' of funny little men like Froude and Bernouilli, Reynolds and others. Perceptive catsailor forum posters will remember that I am a Control Theory major of the faculty Mechnical engineering however in the Netherlands these two faculties were combined during my time of studying all the way up to choice of specialisation. (majoring) So I did large segments of both.
"but you seem unable to combine them into an accurate, logical result for other than that which suits your purpose at the time, this is not a criticism, but purely a personal observation."
I will write a letter to my professor at the time that he should give me a failing grade as it has been found out on personal observation by mr Barrett that this theory is all wrong ! I hate to do this to him however as the whole faculty must revise their courses.
>>"Have you not noticed that an ice yacht far outperforms sailing craft (on liquid water) of ANY size and power, by many times?"
I sail class 5 landyachts, and you ? Not much wave-making drag or wetted surface drag going on with ice/land-yachts is there ? Or are you the kind that uses Froude's law for cars as well ?
>>The ice yacht is sailing on water in its solid form but it is still sailing IN water in its liquid state due to the pressure of the blades on the surface of the ice at point of contact.
You're talking about scating to a guy in a nation that hosts several large speed scating contests every year. As a result scates are under research at the university for a decade now. This theory of liquifying of ice under pressure is still controversial even after many years of research. So I don't know what to say about that, I do however know enough to say that the scates do not carry the yachts weight by virtue of water displacement and so wetted surface drag and wave-making drag is pretty unapplicable to this example. So why do you use it ?
>>perhaps explain why there exist the differences between a Tiger for example and an A class, their differences far outweigh their similarities.
Why should I ; Such a comparison is as entlighting as comparing a Tiger to a Farr 40. Too many variables. This is a stupid thing to do. I trust this is a reply to my comparison between a Blade F18 and Blade F16, however these two HAVE THE SAME hull shapes and share therefor every conceivable hull ratio in addition to similar rigs. Meaning a lot less variables. Therefor these are not so different. Alot can be learned from this. And if you want I also made a comparison between the very different hull shapes of the Inter 18 and Tiger catamaran that by virtue of the F18 rules are extremely comparable in overall dimensions and setup. This is a far cry from comparing a A to and F18. Darryl if you do not grasp such fundamentals then how dependable are the results of your own claimed experiments ? Experimentation is all about changing a few variables between test and trying to explain what happens.
>>To take only a small few of these differences and try to say this is why, no matter how many established principles and theories you try to apply is invariably going to lead to incorrect or at best, subjective conclusions.
First I refer to my answer above
Secondaly : so what are you doing ? On the same approach you explain that what I explain is not true so where both guilty of the same crime if either one of us is ? I only want one thing that you scientifically develop your counterargument.
I don't mind that some people have funny idea's but I do expect them to explain how they are founded on generally accepted foundations, not on wether they knew Bethwaite personally or how their pocket knife moves through the water.
>>applied Marjac's theories with success to my own commercial designs
Maybe I should help you out here. Pardon me, but your commerical successes are pretty minor. You ain't no ORMA 60 designer, Bruce Farr, Hobie Corp, Martin Fisher or who ever else of international fame. Your Alpha-Omega designs are limited to Australian region and are very unknown to any other part of the world. No other rating system then Australian systems list your products. Your succes is dwarfed by your local competitor AHPC and to be honest I never even heard of your boats before you contacted my some time back about F16. None of your designs ever achieved major succes in a class event against other designs (designers) like the A's or F18's. For all we know you design duds, knifes that travell throught the water on their sides. Now I do believe you can design a good boat but refering to your "commerical successes " is not a very convincing way to proof that.
Now lets get this straight. I'm not significant in the commercial sense myself, not even close, but you ain't much better. So lets stick to the scientific facts and argue on those please.
And ohh, yes, I was never impressed by "show of credentials", not even when in university. What you say must make sense otherwise anybody, no matter how established their cred, is simply wrong.
Wouter
OK, boys, take it outside.
Woot, if its for DB "only" please hit the "send a private message" button. Save us your...whatever.
Peace on Earth...GOOD WILL to all other sailors! Have fun! 
Get a life.
I'm not Darryl...but "I ain't no backwater hick" sure makes you sound American! 
(and isn't Darryl an Aussie?)
"If you don't like the message, kill the messenger" sounds appropriate. I don't like replying to rude, ill-mannered, PERSONAL torts, life is much to short, all I will say (and the only reply I will make) is that you are not the only one that posts here that has the appropriate qualifications to offer a valid evaluation on "sailing" and please don't treat me in the same way as you have previously done to "Bill Roberts", we are different people!
Darryll,
Just give me the explainations of your theory after which we can discuss this in a scientific manner. Up till now you have only said that I'm wrong without any real explanation; simply on the basis of some unspecified experience, a knife on its side, "personal commercial succes" and on a intepretation of Marchaj and Bethwaite I can't really underline. THAT, my friend, comes awfully close to ill-manner PERSONAL torts just as well.
If you say that a person is wrong in public after he has explained his position in detail then you are REQUIRED to explain yourself in detail !
Man, I'll tell you why I react so heavily to this.
I'm so sick and tired of people saying something is wrong without ever explaining why. That you must trust their blue eyes or "commercial success" to proof that they are right.
And then the degrading "Formulations you gleaned up somewhere" ; what are you trying to do here ? That I'm the one who is being personal ? That because my name is Wouter ; I can't possibly have a background in this field that you just can't push aside easily ?
And why do you bring Mr. Roberts into this. All you have to do is show the superiority of your experiences by writting my intitial posts using your theory and proving me wrong. Bringing in Mr Roberts is just another tacktic to get out without having to substantiate your claims.
Darryl, don't think this is something major personal. It is only personal to the extend that you effectively called me a "know-nothing" and "wrong" without substantiating in detail the grounds for such.
And yes, I do demand satisfaction in this case. Knowing full well that whole universities theorize along the lines that I layed out as well. You have to be some Einstein to substantiate your foundations against that.
Will the other forum members look down on this thread. Most likely, but then again if they don't understand the line "For Darryll Barret only" then they have only themselfs to blame. Besides, they know me from the past and know full well how many times I've been right despite overwhelming opposition. They would do well to understand what is yet again happening here. If they want to remain stupid than that is there choice.
So Darryll, do me a favour, kill me off permanently or make a fool out of me by proving that your theory is superior to mine and explains better what will happen with the M18. IF you do not or can't do that then make sure you have the personal pride to accept that YOU were wrong and that YOU didn't know what you were talking about. And be man enough to publize that in the same manner you made your other posts.
And with regard to your latest post, 68 wasted words, don't spring off in all kinds of unrelated directions and think that that makes a meaning full reply.
I challenged you to proof me wrong and show the superiority of your theory. (use the M18 subject please) If you don't step up to the plate than you are just another fool who claimed something he can't proof if his life dependent on it.
Be a man and defend yourself
Wouter
Wouter
From reading the posts associated with this thread I can't see why you are taking such offence.
I think the knife example is a good one,
You seem to be arguing about whether wetted surface area drag is more important than wave drag. I think this argument is really about semantics. I don't think that the "wave drag" that you are talking about is the same as the "wave drag" that Darryl is talking about, and neither is the "wetted area drag"
When you first talk about wetted area you present it as only as that i.e. a situation based only on the surface area of the hull. From that you could infer that the best shape for a Cat hull is half a sphere. But in the "flame post" you say that what is causing the extra drag when you turn the knife sideways is WSA drag. So when you are talking about WSA drag I think you are really talking about what I call form drag. Am I correct Wouter? If you were talking about WSA drag then you would have to concede that the drag should be the same no matter which way the knife was dragged through the water.
Equally when Darryl talks about "wave drag" you assume he is talking about the Froude law = constant * sqrt (waterline length) wave drag. But Darryl then talks about his wave drag meaning efficiency. I think he is also confusing wave drag with form drag or drag caused by the shape of the hull not by its wetted area.
Indeed I could be making things even worse because what really is form drag?. At the end of the day drag is complex and is made up of many elements and is in my opinion too complex to predict in real terms. The formula's that Wouter uses are valid but whether they are more valid than observation and experience is a matter of opinion.
For Wouter to say that the only valid arguments are those based on science not personal observations is in my opinion wrong. When I read something I disagree with I think "why does he see it different from me", not "that guy is obviously stupid".
I can't see anything in Darryl's posts where he implies you are a "know-nothing" he is simply offering a different opinion based his observations.
Thank you Grob,
This is what I want. A discussion on relevant arguments. I will respond to your questions in kind.
First I demanded that we discuss this topic under the framework or scientific methodogy as what framework are we left with when we won't use this. We must limit ourselfs to a given framework otherwise all comments are void of any base. I proposed the normal scientific base as that the one that is most commonly known, understood and the most developped one.
The methodogy encloses :
- Disproving a theory by providing a counterexample that isn't accurately described by the theory.
- Providing accurate predictions in a few key examples that are explained accurately by common knowlegde and other theories. Linking it to a greater system, not proving something because it is accurate in one particular example.
- Limiting oneself to commonly understood factors. So no "wonder tissue" explanations.
>>From reading the posts associated with this thread I can't see why you are taking such offence.
I took that because somebody claimed that the theory I used was wrong and therefor the conclusions were wrong without providing a counterexample or explaining what was right. This implicitely made me out to be a liar without putting proof to the cause. It was aggrevated even more by the fact that I know how well linked the used theory is in the world of science and experiments. I simply can't stand that somebody just dimissed such a thing with a flick of the hand.
>>I think the knife example is a good one,
First it fails the counterproof requirement as my theory doesn't say that the drag in this case is mostly from Wetted surface drag. Actually my theory as well stated that drag in this case is almost exclusively form drag combined with wave making drag. So Darryll thought up a counterexample were, presumably, both our theories predict the same outcome therefor this example can't be used to descriminate between the two theories.
Also the fact that form and wave making drag is dominant in the knife on its side example says very little about which drag is dominant in the knife parrallel to movement situation.
It is only in the parallel case that our theories differ.
Hence my counterexample about the "knife in Honey"; intended to show the relation between viscocity and drag when the knif is held parallel to movement. This suggests that viscocity related drag is dominant in this case which leads to wetted surface drag being dominant.
>>You seem to be arguing about whether wetted surface area drag is more important than wave drag. I think this argument is really about semantics. I don't think that the "wave drag" that you are talking about is the same as the "wave drag" that Darryl is talking about, and neither is the "wetted area drag"
Actually I'm not arguing that. You guys must understand the meaning of the conditions set out in the thead and in my initial posts.
We were talking about catamaran and very light weight catamarans. Boats with very slender hulls and very small displacements for a given hull length. IN THIS SITUATION, the wetted surface drag is dominant over the wave-making drag. This can NOT be extrapolated to situations where not all of these conditions are satisfied. For example the knife on its egde situation. I didn't claim that wave-making drag is never less dominant than wetted surface drag. Just that in the case of these catamarans it is.
Actually Froude's law is the law that predicts that wave-making related drag becomes dominant at maximum theoretical hull speed and when you satisfy the conditions set for using this formula (like most yachts do) than it accurately described the situation. However the catamarans do not satisfy these conditions in the same way and Froude's law give a false prediction in this case. You must know the background to Froude's law to understand these conditions. I won't go into that now. A hint; Froude actually didn't predict what happened in terms of drag but what happens in terms of the wavelength of the bow and stern waves at a given hull speed. It turned out that this was strongly linked to the rise of wave-making drag to an extend that yachts wouldn't go no faster. Less scientific based groups and persons quickly intepretated the Froude law as a drag prediction law which in basis it isn't.
Semantics :
I use as wave making drag = the drag that is associated with the energy that is lost when a hull creates a watersurface in oscillation when before it was flat.
I use as wetted surface drag = the drag that is associated with the reactive force that is created by the viscocity of the water running along the hull.
I thought Darryll was using the same definitions. They are afterall the commonly accepted definitions of the two forms of drag.
I do admit that there is a 3rd component which is form drag, however this one is often included in the wave-making drag as it is very difficult to deperate the two when looking at surface ships. For example with submarines all three can more easily be seperated when the submarine is not sailing on the surface.
In my initial posting I expressed that the common accepted rule of thumb that a longer hull has less wave-making drag is simply wrong when looking at catamarans (it is right when looking at keeled yachts ! ) Texel system however does not recognise this fact. I say fact as this 'wrongness' is known well enough and has been proven many times over in scientific circles. THis is part of the explanation of why Texel rating gives a stunningly low rating to the A-cats and M18's.
>>When you first talk about wetted area you present it as only as that i.e. a situation based only on the surface area of the hull. From that you could infer that the best shape for a Cat hull is half a sphere.
If you read it like that you can BUT I by going to a sphere are no longer satisfy the condition of the long slender hulls like catamarans which was ery much the basis of the discussion. I expressed, or at least hinted at it, that in the case of sailing catamarans wetted surface drag was dominant over wave making drag. I never expressed that this was always the case.
This is alway where the knife counterexample fails. The knife on its side does not resemble the slender hull of a catamaran in any way except when looking at side ways drift. Arguably that was not what was the core of the discussion.
>>But in the "flame post" you say that what is causing the extra drag when you turn the knife sideways is WSA drag.
No I did not. I said that if you turn the knife back so it is parallel to the flow that something else must cause the drag you feel as due to minimal crossection both the form drag and wave-making drag must be to small to feel. Enter my honey example. Pull the knife vertically out of the honey and you'll feel the wetted surface drag now compare this to drag when pulling the knife through the honey. There isn't much difference is there ? So what does this say about the ratio between wave-making drag and wetted surface drag ?
Now take something like a tube or stick, thus leaving from the condition of long slender hulls, and pull that throught the honey. Now wave-making drag has become far more noticeable contribution to the overall drag. However that this is happening doesn't say that the wave-making drag with the knife must be dominant as well. We know from this experiment that it can't be. This shows us that we must take care to understand that results may differ greatly when looking at very different setups. If we want to say anything about the long slender hulls of both the M18 and F16 then we better make sure that our example resemble these. Their is not much point therefor looking at counterexamples that feature VERY different shapes like spheres. Or even blades of a knife. People familiar with Reynolds numbers understand what I mean in the last phrase. Things can be so dependent that even results from scale model testing can not be extrapolated to full size situations. This is an interesting topic in itself but not for now.
>>So when you are talking about WSA drag I think you are really talking about what I call form drag. Am I correct Wouter?
No, I'm sorry you are not correct in this.
>>If you were talking about WSA drag then you would have to concede that the drag should be the same no matter which way the knife was dragged through the water.
No, I don't have to do that. I refer to my explanations above. Depending on how you hold the knife the dominant factor in overall drag transitions from wetted surface drag via induced drag (result of lift vector angling backwards) to pure form drag.
However the fact that oen is dominant over the other in one particular situation doesn't say any meaningful of what must be the case in another situation. We all accept this readily when looking at airplane wings but not when looking at hulls or knifes. Why is this ?
>>Equally when Darryl talks about "wave drag" you assume he is talking about the Froude law = constant * sqrt (waterline length) wave drag. But Darryl then talks about his wave drag meaning efficiency. I think he is also confusing wave drag with form drag or drag caused by the shape of the hull not by its wetted area.
I can't comment on that then suggest that we all use the commonly defined definitions as expressed in Naval engineering and science. I know that I've used these.
>>The formula's that Wouter uses are valid but whether they are more valid than observation and experience is a matter of opinion.
That is true, however these formula's are based on real life observations and experiments as well. To state that they has not much compelling to say about what happens in real life is a bit misguided. I know it is fashionable today to look with disdain upon conventional science but that doesn't mean it is wrong. Many people over many years worked on this to make it as accurately as possible and to proof it under challenging minimal requirements of acceptability. It will be a fools action to discard this just became he thinks that he saw something else happen when sailing last sunday afternoon.
More often than not it is a human being who makes an error of intepretation rather than a theoretical model being wrong.
Froude's law is a great example of that, Explanations of slot effect between jib and main are another. Some of these have been disproven in certain special situations some 100 years ago and still these discredited theories are commonly encountered among sailors.
>>For Wouter to say that the only valid arguments are those based on science not personal observations is in my opinion wrong. When I read something I disagree with I think "why does he see it different from me", not "that guy is obviously stupid".
The guy was stupid because he could substantiate his counter claim in any meaningfull framework. maybe if he completely redefines WSD and WMD he can make his theory work. But then again, what is the use. He'll be the only one using these definitions and everybody else will be completely confused by it. There is definately something to be said for conservative classical scientific methodogy. More than anything else it ensures that everybody speaks the same language and avoid endless confusions this way.
Regards,
Wouter