Trimaran Design Concept with longer foils than the main hull

Discussion in 'Multihulls' started by boradicus, Jun 3, 2013.

  1. boradicus
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    boradicus Senior Member

    Thanks to everyone for the various book recommendations! I decided, actually to go with Derek Harvey's book and ordered it because I found one that was cheap on Amazon. I figure a book in the hand is worth... well, worth more than two in the shopping cart lol!
     
  2. cavalier mk2
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    cavalier mk2 Senior Member

    Yes Boradicus, if the heart and mind are united with the seat of the pants you have a good chance of success. The Chris White book is good and a standard, the books by the sailors are a good introduction because they tend to cover use without having anything to sell.
     
  3. boradicus
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    boradicus Senior Member

    Another analog for this would be something along the lines of the heart being representative of a unity of of will, to which the mind, or the rational process is applied, as you say "by the seat of the pants," or on the fly, at every instance, etc.

    We could say, "adaptability, coupled with presence of mind and steadfast determination of will is the most likely combination for success." :D

    What did you think about that Russian designed trimaran? Pretty cool looking...
     
  4. boradicus
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    boradicus Senior Member

  5. cavalier mk2
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    cavalier mk2 Senior Member

    I haven't looked at the Russian tri yet.....The seat of the pants thing for me refers to "feel". My son and I have taught sailing to many of his classmates and we both learned that some people have a natural sense of feel and awareness of the physical world and others couldn't steer straight if they were on rails. They can learn (in most cases) in time but are a bit less connected to cause and effect. All are very bright so it isn't a mental thing. The heart thing referred to interaction on a emotional level, the sense of pleasure and joy sailing brings for example.

    Math is a great descriptive language, wonderful in its lack of ambiguity. It is great for conscious level assessments of what is happening but everybody seems to process cause and effect whether they have advanced math skills or not.
     
  6. boradicus
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    boradicus Senior Member

    With respect to advanced math, I am trying to understand how to approximate the length of a curve. I am going back to a basic calculus book to see if I can find anything there. I believe what I need is a text to explain integration of a convergent sequence, but I am not certain about that just yet. What I am currently trying to do is to learn a way to estimate the wetted surface area of a hull. I think that Skene's explanations leave a lot to be desired, and so I am trying to understand getting the wetted surface area using my own noggin :) I believe the best way to break it down would be to realize that the length of the longitudinal curve of a typical mono hull probably conforms best to a logarhythmic function, which tends to straighten out from stern to bow rather quickly, and that I would then need to integrate the various areas between each vertical station, using another function to estimate the vertical length of the curve of each station from bilge to gunnel.

    Once I can figure this out, I think I can begin to look at designing the main hull and then the outriggers, which by comparison, due to the comparative regularity of their shapes, should be a lot easier to deal with.
     
  7. boradicus
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    boradicus Senior Member

    I am not that advanced in calculus, but what would be really cool is if there was a way to find a way to take the integral of the series comprising the length of the longitudinal curve of a given arc from stern to bow, and the integral of the series comprising the length of the curve from bilge to gunnel at any given vertical station and to combine them such that the product of both vertical station length and stern-bow length could be combined as a matrix of cross products to be integrated in a single function that would result in the wetted surface area. Hrmmmmm....
     
  8. cavalier mk2
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    cavalier mk2 Senior Member

    You are busy....we think you're being a bit vague though. Have you considered checking the computer design threads ? Send more data for the math class. How are you designing these curved hulls, are you using a function to specify the curve or are you using a sequence of data points like a lines plan? While Gary is busy with his godless activities I'm in a hurry with some heathen, pagan stuff.....(darn monoliths)
     
  9. boradicus
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    boradicus Senior Member

    I'm an abstract person - so if I seem vague it is most likely because my thinking requires greater definition. I don't really know what I am talking about, and as a result I am trying to ask for help the only way I know how - which is to attempt to define what I think might be possible... I don't really know if you can take two integral functions and matrix a cross product out of them or not. I am certain you could do it with some code, but that is not as elegant and sleek as using a single formula. I also like formulas better because they tend to scale better when you are in actual need of creating algorithms that use them.

    In response to your specific question about using a curve or a sequence of data points, I am not using a sequence of data points, but I what I would like to be able to do is use a formula to project them - sort of like how Tom Speer does with his Basiliscus - although I don't understand quite what he is doing. I know he mentions using the Fourier Series. Can any of you enlighten?

    Sorry for being vague - doing my best here!! :*)
     
  10. boradicus
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    boradicus Senior Member

    To get a hull shape, Speer seems to be working backward from the LWL and CB to get his LOA:

    X = [-.5*cos(ѳ)-1CB(1-cos(2*ѳ))]*LWL

    with 0 <= ѳ <= Pi

    He says he is using a Fourier Series to do this, which I don't quite understand, but I think it would make more sense to me if I understood better the basic relationship he is getting at here with respect to CB (center of balance), LWL, and LOA.

    Any takers?

    I am still muddling my way through Skene, awaiting the books I ordered...
     
    Last edited: Jun 6, 2013
  11. Doug Lord
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    Doug Lord Flight Ready

    bora, I strongly urge you to not try to reinvent formulas for which perfectly utilitarian ones exist-for instance, for wetted surface. Learn to use those and after that you could rewrite the math. Depends, I guess on how soon you want a basic capability in calculation? Boat design is a big subject-if you get into rewriting perfectly good formulas you'll be spinning your wheels and getting nowhere.......
    Just a suggestion: design and build yourself a small boat or two-even models-but preferably something you can get in and sail. To design well you need a "feel" for how numbers affect an actual boat.
     
  12. boradicus
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    boradicus Senior Member

    Doug, thanks! I will definitely take that under consideration! I think what I am working to hard to understand is how those formulas work so that I can understand what I am doing. My process for understanding something whether fortunate or unfortunate (how you look at it at the time) comes down to being able to reproduce something on my own - probably why I enjoy messing about with designs!!! If I can just figure out what the Secant Method is and how it works, I might be better able to proceed. But in the meantime I am trying hard to grasp some of what I see out there and to make sense of it. I think I will be better structured in my approach once I have a decent text in hand - I hope! :D Thank you again!! And I love what you are doing with your foils. Those Moths are really neat! I hope your model works out well!!
     
  13. boradicus
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    boradicus Senior Member

    Okay, now I get what is going on in with Speer's design better now. I just found out that CB doesn't actually stand for Center of Bouyancy but Block Coefficient (at least I am leaning in that direction!)
     
  14. Richard Woods
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    Richard Woods Woods Designs

    In general coefficients have a capital C, so Cp, Cb etc. Centre of buoyancy is CB, but clearer, CofB, centre of effort is CofE

    I also think you are getting too bogged down with the maths involved. Most multihull hulls are long and thin, so for initial design estimating you can get a reasonable approximation by taking the mid girth x LWL and multiplying by a constant to allow for the fact that the hull gets thinner at the ends.

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     

  15. oldsailor7
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    oldsailor7 Senior Member

    I use a simple mathematical rule of thumb to gauge displacement volume, which can also be used to gauge wetted surface by calculating the surface areas.
    LxWxD in feet below the waterline, gives the volume of a rectangular box.. Multiply this by the prismatic coefficient to get volume. Multiply again by 63lbs/cu ft, (or 64 for sea water) to get displacement in Lbs. If you don't know the prismatic coefficient use .67 as a typical average.
     
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