Sorry ,-
typical designer ,-off on a different tangent -as usual

Really enjoy cat design posts --own a Supercat so am a big fan of Bill Roberts ,--also the same last name as mine ,-so in the past I,ve recieved questions from others that confuse us ,--that I refer to Bill on specifics of cat design .He has a tremendous working knowledge and readily available applied engineering formulas . --great stuff and really appreciate his posts .

Wout has done a very good job along with others input on the F-16 .

interpretation -
responded to earlier posts on sliding seats and their history applied to cat design .
The post commented on sliding seats and earlier W-1000 innovations of 10 ft racks mounted on travelers .also commented on patten searches and concepts and ideas over time ,--

Sail 7 seas responded with a comment on platform shoes etc of the era -
the return post was an attempt at a humorous responce on the era also with some added philosophical comment ,off on a different tangent -thanks Mary

Kev ,-thanks we are the same age so share similar experience and thoughts on numerous subjects -

Dav Ho --always good to read your posts --
It IS one of the best threads in a while
each have their own experience and perspective ,
Not sure if its a cultural thing but Wout often comes off as Bill noted as being "distastfull" in opinions offered .
needs to work on that as I do ,--thats why its recognized.
MAHALO
from a former Kaneoe beach cat sailor ,

Thom ,-- thanks ,-can;t see or spell worth a %$#@@#)%

.-Mg H-17 --It helps --but not recommended .

Been attending graduation cerimonies --so thought the Harvard speach from 78 that I ran across in other articles was timely and an interesting look back at the era --
then of big shoes --big hair -etc as sail 7 seas noted -
read it if you get a chance --link on the post
its fasinating -

"we have no where else to go ,---but upard on the evolutionary scale ,--

whew ,--

conversely also liked this web site -
http://stupidity.ca/

have fun
Carl




-

Mary,

It may probably be best if you named the individual parts you find yourself struggling to understand. Otherwise there will be to much to write.

vortices :

really something common. That funnel that you see when you empty your washbasin is a vortex. A tornado is a very large vertical vortex. Vortexes on the tip of wing (or any object that has a high and low pressure side) are just invisible horizontal spinning (around centreline) volumes of fuidum (air) and are called Tip vortices. However similar spinning volumes can be found on leading and leech edges as well depending on the design of the object. They can also be found behing chimnees and buildings. A vortex is a special type of turbulences. In general it is turbulence with a highly predictable and uniform shape. General turbulence moves all over the place while vortices can be very clearly defined. Dependent on their rotational speed these vortices can sap alot of energy from the pressure difference that is causing then. Of course energy is the final baseline of all processes. The sail develops power by milking energy from a energy rich medium.


spanwise flow : Just what is, says flow along the span of a wing.


Mary, you said that your father indicated that sails are pushed along.

How strange it may seem but many tests have shown that a wing section experiences much greater low pressures on the leeward side than high pressures on the windward one. So there is indeed a push component on the sails but a far bigger of the portion is the sailpower is developped by an underpressure (low pressure) on the leeward side.

Mary, the hard part is that fuidum mechanics and fluidum dynamics is a very strange world and often it is just a little different form what you would expect. Our dear God had a really jolly mood when he worked on this area.

One example is that a flow through a pipe at the part where the pipe narrow and then widens again will first drop in pressure and than rise back to normal pressure instead of the other way around. This is called the Venturi effect. Normal people will just expect the very opposite.

Anyway, what else do you want explained ?

Wouter

You may be above my head... I've got to sit down and think of laymans terms to put all this stuff in.

Write a book :P

Most of this thread has been about individuals arguing engineering theories applied to boat design. They are called theories for a good reason. In reality there is very little engineering fact when it is applied to the real world. Things are far too complex. Engineers use the theory to guide them toward a design. Bill Roberts designs good cats, it doesn’t matter if you don’t believe in the theories he has used to reach that design. The proof is in the pudding.

A good example of this is Mary’s proposed sliding mast design, in reality it will not give a larger righting moment see http://www.wingo.com/proa/rig_placement.html ( I think that is what she was getting at, forgive me if I am wrong). But if she went and built it she would probably find it does give more power for a number of other reasons, so building something based on the wrong theory is not necessarily a bad thing. The important thing is to try things out.

Mary, if you or any other non engineers want to understand engineering better I would recommend the book “Structures or why things don’t fall down” by J.E. Gordon its available in paperback about $12 on amazon.

In boat design, because conditions change every time you sail, then its nigh on impossible to say you have a better boat than the next man. Using a system of rules narrows the field down and allows a little more comparison, which appeals to many people (not me). I believe the ultimate measure of a boats performance is the size of your smile. If you hadn’t guessed I am a design engineer (engines) and amateur boat designer/builder and my interpretation of the theories are very strange indeed.

Gareth Roberts (no relation to Bill or Carl)

A friend of mine just finished building one of these (CLC Proa Mbuli). We'll be launching it next week. Hopefully I'll have photos to post. (sistership shown below) Believe it or not, you can actually go below decks into that coffin-like cabin

Grob,
It was not really my idea -- just a visual interpretation conjured up in my mind based upon Luiz's explanation about righting moment. The book sounds interesting, but I certainly would not want to limit my creativity by learning too much about the laws of physics.

Ok, moderatly long winded but hear me out. I'm gonna bill this as a blend of Bill and Wouters statements.

My favorite comedian is George Carlin. He does a bit about license plates and the things that the states put on them for slogans. One of the states that he mentions has “Live free or die!” on it while another has, “Famous potatoes”. He comments on the absurdity of these two and states that the truth of the world probably lies somewhere in between.

I think this whole discussion is in the same ballpark as George’s bit. The real answerer is some where between Bill’s brute force method and Wouter’s extreme finesse.

The construction techniques available to us today are much more advanced at a more reasonable/reachable price than in the past. Carbon is still exotic, however much more becoming the norm for many components. We can decrease weight, increase strength and produce a mast which will bend anyway we want just by adding a little carbon here, removing some there. Producing not only a lighter stronger mast, but one that is possibly more effective across a wider range.

The laws of fluid dynamics have not changed, but our understanding of them has improved. Not only our understanding, but also our ability to more accurately model the flow of fluids across sails, hulls and other appendages. When I was in ChE class, our professors would have us do more work on a problem than was specified in the book. When we asked why, he replied, “Your books were written in the 50’s, since then computers have come a long way. Since you do all of your work in MathCAD, you can more easily do the complicated calculations that are required.”

Older hull and sail shapes designed by paper, spreadsheet and slide rule would take drastically longer to design than newer ones done with the current crop of software. The older shapes would most likely be less efficient than their new counterparts. By “hand” we can only calculate a certain number of intervals along the hull to judge the effectiveness of the design. While the software packages can do extraordinarily finite calculations across the entire surface to produce a more accurate picture of what is going on with the hull and sails. Some of the software (I think I saw it somewhere) is not only looking at the hull through water, but the hull and sails as a complete package with wind and waves. This provides more information than was ever imaginable before to determine the optimum direction to take the hull design in.

The best designs are the ones that not only provide for a great deal of power, but also incorporate it in the most efficient package possible while staying manageable across a wider range. I think the true art of design is knowing how to find the optimum middle ground…not only power, but efficiency also. Realizing that not only power and efficiency are needed, but look at things like momentum. The HT was on the efficient end of the spectrum, but look how it does in waves….or doesn’t when the wind is light. A down fall of that particular design.

Wouter and Bill are both coming at the same problem in two different directions. Wouter has probably spent more time behind a keyboard while Bill more time at a drafting board. I can’t give an edge to either design method because there is much to be said for both experience and computational ability.

I think I read the statement earlier in this post about formula rules limiting creativity (or something like that). I think it is completely to the contrary. If given a set of design guidelines I would expect it to take much more creativity and ability to produce a winning design. Since the major parameters have been established (LOA, SA, beam, mass) your brute force (SA/mass ratio) has already been determined. To create a more flexible and effective platform within those guides would require more resourcefulness to get the most out of the available power.

Look at two similar designs, the I-20 and the N-6.0.


These numbers straight from the Performance web page
I-20 US 390 lbs 246 ft^2 SA/wt=0.6308
N-6.0 NA 420 lbs 264 ft^2 SA/wt=0.6286

The sail area to weight ratios are VERY similar, however the I-20 beats the 6.0 upwind. (I only mention upwind because with today’s Bermudan rigs, they are mostly optimized for upwind.) Why is that? More efficient platform I suspect (hull shape, square head, aspect ratio of foils and sails). I would also suspect that the I-20 has also had more time put into its sail plan optimizing it for upwind (since it was designed for a spi).

I’m no expert, but I think your both a little crazy/fanatical (did have some psych in college….)! You both believe deeply in your design philosophies. Like I said before, I think that anyone can make a boat faster by adding some sail or by improving it’s efficiency, however if both are not considered together the end result will be less than equal to it’s full potential.


Will R

Will,
I agree with you that it takes more creativity to design within a formula. It's sort of like poetry -- it is easy to write free verse but takes much more discipline and creativity to write within specific parameters of rhyme and meter.

exactly -
a wonderfull syncronisity exists connecting many things -

An interesting series on the history channel by Berk showed inventions of very different sorts over centuries -the successes and failures ,-most importantly how these discoveries and inventions effected one another in development ,-and how interconnected it all is as one could not have been created without other related earlier attempts ,---one builds on the knowledge of another and another creative result of engineering and design often through trial and error process .

really like Gareth's {grobs} 4 hull design -
http://www.caemodel.co.uk/boat.htm

think it would also be great without a sail -
just as a fold up -cartop paddle-boat with added seat and maybe peddle driven prop and rudder ,--ideal lightweight stable fishing platform or just recreational watercraft as well as alternate sailing craft ,-

He most likely has already thought of the many other applications ---fun stuff

check it out --congrates Gareth !!

http://www.caemodel.co.uk/boat.htm

Well hello everybody,
I'm glad to see the title change. An engineer is the person who takes all this theory stuff and makes it work in practice.
In 1981 I went over to Brest France to the World Championship Speed Trials for Sailboats. There were mostly sailboards and beach cats there. I was obvisously interested in the beach cats. There were boats there of all sizes, 14ft to 20ft, and descriptions, all the popular classes plus sone one of a kind boats. There were three days of speed runs and every boat was allowed to make as many runs as they wanted to until the clock ran out. The results were calculated by computer and printouts were available every night of every run on every boat that tested that day. I brought those results home with me and studied them and tried to figure out why some boats were faster than others. I knew the old formula, Vmax = 1.4 sqrt LWL. The 1.4 coefficient is called the speed to length ratio. I solved for the speed to length ratios for the fastest boat of each size and then tried to figure out what could be making these ratios or coefficients vary between 4 and 5. I considered hull loading, displacement/length **3, bow wedge angle, work and power of pushing the water aside and many other parameters were considered. What I finally realized was that when I plotted speed to length ratio vs hull fineness ratio the data defined a line that was almost straight. Then I connected it to the 1.4 value for monohulls at a hull fineness ratio of 4 and it too fell on the line. Well now, how about this, we now have a Simple Simon way to estimate beach cat max speed based on boat length and hull fineness ratio for boats in the 14ft to 20 ft length. This I have used in my boat design calculations and it has served me well. I have predicted the Portsmouth Number of the boats I have designed using this equation and many other parameters and ratios and hit the PN of these boats right on the money every time. And for Wouter: This system is not the first law of catamaran boat speed but it is a system that I have come up with and it works very well for me.
Here's another Wouter point that I should respond to. Wouter is bringing forward the position that as boats are built lighter in weight with higher sail area to total sailing weight ratios they can go faster even though they have lower righting moment to sail area ratios. I have a hard time going along with that. I know of no example where that is true. Wouter pointed to the A class cat as an example of success here but I don't go along with that because the A class cat is a development class and many things are improving about that boat as well as the weight going down. I am not willing to give weight reduction total credit for the performance improvement in the A class catamaran. Wouter also pointed out that the Tiapan4.9 was lighter and faster tham the H16 and the Tiapan is the same width and length. Not a fair comparison, Wouter. I think the Tiapan has daggerboards and you can't compare beach boats to board boats on performance. The board boat is faster every time. We do have this comparison: A year or two back they held a trials in Europe to consider a catamaran to replace the Tornado in the Olympics. All the new hot 20 footers took on the Tornado. The Tornado won every heat. WHY??? The Tornado has a higher sail area to weight ratio and it has a higher righting moment to sail area ratio than any of the other boats in the race. Well done basics, fundamentals, will win every time.
Bill

This thread has brought forth many different opinions and ideas relating to catamaran design...always interesting to hear different perspectives.

However, when it is all said and done, to the best of my knowledge, no one who has responded to this thread has the "proven track record" (encompasing both race winning sailing and design expertise) that Bill Roberts has exhibited over the course of his life time.

It is one thing to theorize about what may or may not work based on opinion, or a computer model, it is a different story to have a solid history to back up your position. We have to remind ourselves that while computers make many things easier to calculate, it still is in essence a tool. It is only as good as what you put into it...

It is amazing how bold we can be when sitting behind a key board...basicly challenging a successful and inovative aeronautical engineer/catamaran designers whole carrier based on our elementary understanding of sailing and boat design (in most cases)...Or at very least without the benefit of his years of practical experience and experimentation.

It is a real blessing that Bill comes on this forum and take the time and energy to respond to questions with detailed technical explanations. Blending engineering skills and practical experience, he is uniquely qualified to help us all...Let's make sure we continue to give him the level of respect he has earned.

Bob

The ISAF trial occured in March of 2000 in Quiberon France. The Marstrom 20 hit an underwater cable early in the week and was not able to sail (due to broken daggers) till the last day. An exert from an article, "The Marstrom 20 finally got out on the water. It had hit an underwater steel cable early in the week and was out of action pending repairs. In the only race it sailed, it walked away from the fleet."

The whole article can be found here: http://old.cruisingworld.com/2000/03/isaf5.html

I have a spreadsheet at work with a lot of the current popular US boats on it. Their weights, SA's, LWL, beam and DPN. I had Excel calculate the SA/wt for each of them. The M20 had something on the order of 1.1 ft^2/lb, more than anyother boat on the list.

M20 54.0 [58.0] (55.8) (54.0) [52.5]
TORN 58.8 63.0 60.9 58.5 55.5
RC-30 53.9 56.0 54.5 (52.8) 50.7
NI20 59.2 62.8 60.2 58.6 57.1

Interisting thing I see here is how similar the T is to the I-20. However what is more interisting is how much faster the RC-30 isn't vs the M-20. 100k??? dollars vs. ~17k, 30 ft full carbon monster (brute force) vs. a 20' modern "balanced approach" design. The boat is light, wide and carries plenty of sail.

I think it is undeniable that PROPERLY applied technology will always win over an older design, no matter how good.

I stopped believing in wise old men quite a while ago when I found that in some classes taught by long time professors I had to make deliberate errors in my exams to get a passing grade. And I was not the only one, the whole class did it and knew it. We tried to explain it to the professor but his only reply was :"Why do you as a young student think that your answer is better than mine, being an professor in this field for many years now". As if the universe and law of physics (aged 5 biljoen years) give a damn about some misguided professor who was able to reach the age of 55.

The 5 of us got sick of this self glorifying answer tactic and left it at that. The next exam we ignored all constants like 1/2, 1/3, 1/4, ... and so on and wrote down answers that were always a factor 2, 3, 4, 5, .... wrong and we passed the test. I must say a really saddening experience.

In hinsight this was one of the most instructive episodes of my university years. Now I look only at the math and derivations made by people and never to the age or the background of the person who has made them. Afterall 1 + 1 = 2 even when a 90 years old professor with 10 nobelprizes for mathematics says 1 + 1 = 3.

Wouter

But you were right Mary !

Moving the rig to the windward hull DOES increase RIGHTING MOMENT

It does not however increase HEELING MOMENT in that sense mr Speers article is correct.

Grob misinterpreted RIGHTING MOMENT for HEELING MOMENT.

The two are closely linked but they are not the same

Wouter

>>but I think your both a little crazy/fanatical (did have some psych in college….)!

Indeed, I admit to that.

I totally agree with you and I wish to underline the following.

I'm not saying Bill is wrong (apart from his application of the Froude law) but that his way is the only way to go faster is wrong.

I'm trying to show that there is another way to go faster that is not described by Bills statement ;

"Nobody is going to build a boat faster than the Tornado until it has a higher sail area to weight ratio AND a higher righting moment to sail area ratio!!"


I never said his way would not produce faster boats ! That is how some of you have interpreted my statements as Bill has too.

Wouter

As an odd coincidence, I was reading about Johannes Kepler on one screen and Wouter's comments on another. Kepler was one of the greatest mathmatician/astronomers. Here is a brief bio on Kepler (or is this Wouter?).

Wouter, I hope you take this as high praise from a 50+ year-old chem professor. As a tourguide for youthful intellect, I embrace your unbridled enthusiasm!
_______________________



The new teacher for Mathematics of the Province arrived in Gratz in April 1594, at the age of 23. He thought himself a poor pedagogue because, as he explains in his self-analysis, whenever he got excited, which was most of the time, he 'burst into speech without having the time to weigh whether he was saying the right thing'. His 'enthusiasm and eagerness is harmful, and an obstacle to him, because it continually leads him into digressions, because he always thinks of new words and new subjects, new ways of expressing or proving his point, or even of altering the plan of his lecture or holding back what he intended to say. On these grounds his lectures are tiring, or at any rate perplexing and not intelligible.' The fault, he explains, lies in his peculiar kind of memory which makes him promptly forget everything he is not interested in, but which is quite wonderful in relating one idea to another.

http://www.mathstat.uottawa.ca/Profs/Rossmann/Kepler_1.htm

Hi Wout

Hope your not judging all people by age alone !

The "wise old prof. " and others did {though sometimes inadvertantly } get you to think ---and think for yourself to seek truth .
the best thing any teacher can hope to accomplish .

The implication of relating this prof story into an engineering design discussion is not directly relavent to
S C designs and Bill,s accomplishments however .
Interesting story though ,
Seems people often reach a position of authority in gov structured organizations and societies that they have not earned and could not in the real world or open free marketplace where people are free to choose another option.
Sighting age is not the cause ,--maybe socialistic ideals ,-shades or grey or otherforms are more the base cause .
People of all ages continue to be inventive and have creative minds throughout their lives .Examples are numerous in all forms of human endeavor .

Nice that so many good people take time to respond to sailing posts ,--we worry about each other .-each others ideas and opinion ,-try to point to the short explaination and perspective of each ,--

S C and Arc designs have been reasonabley successfull in the marketplace and continue to be -

Bill mentioned earlier that any could take the Arc 21 design ,build a 20 ft--8.5 beam version - take a 1-ft 3 in . off the stern and have an excellent F-20 type cat design . add a C F mast and similar sail plan and it is a speed machine equal or better than most when sailed to its potential .
There is no doubt in my mind that this would be a superior performing 20 particularly for distance ocean racing in seas in races like the Worrell or Tybee 500 .-
Comparabley the current "fastest 2o"-The Inter 20 has large bow sections ,-nearly 16 in in width with very flat underwater profile which slaps and sometimes pounds in waves . It is also skidish and does not track like a deeper narrower hull section design ,-helming is a factor also,particularly in distance racing .

As a Formula racing advocate you must realize the value of this and others options . The underlying reasons why existing design is valued and new innovation and refinement from them is vital for the sport and its future.
Like everything when it becomes stagnant it begins to decline and die .

We will see the S C and Arc designs as well as many design features Bill incorperated into them subsequently applied by other designers that have influenced them greatly and will continue to ,-around for a long -long time .-

-

Wouter,

I didn't misinterpret righting moment and healing moment I deliberatly swapped one for the other. My understanding of these two is that while they have different meanings they are equal and opposite so one can't increase while the other stays the same.

I may have confused what Mary was saying and that is why I apologised to her in advance in the same posting.

Can you explain how RM and HM can be different.

All the best

Gareth

Meek, nerdy student cowering in back of classroom slightly raises his skinny hand, raises his shaky, wimpy voice and states:

Righting Moment (RM) is the force that tends to keep the boat upright. Heeling Moment (HM) is the force that tends to knock the boat over. Shifting the rig to weather will increase RM the same way shifting crew to weather does: The lever arm for the mass of the rig is increased. HM stays the same, because a rig of X height, having a center of effort Y feet above the deck, will ALWAYS have the same HM. Of course, as the weather hull flies, the HM increases faster than it does when the rig is centrally located, as it rises above the water (and the leeward hull) faster.

sail fast