l/b ratios: the longer the better? trimaran float placement?

Discussion in 'Hydrodynamics and Aerodynamics' started by surfbus, Dec 4, 2014.

  1. longcours62
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    longcours62 Junior Member

  2. groper
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    groper Senior Member

    I would suggest that you start sketching out a floor plan or general arrangement of the boat you think you might want. See how much space you have to work with, and where things would go so that you get something that you feel suits your purposes. Once you start doing this, you will fairly quickly see what is feasible and what the challenges are fitting certain things into long skinny spaces. I wouldn't start by drawing an already dimensioned hull. Start by drawing the internal layout first, then the hull around it last. If you try doing it the other way around, you will keep scrunching up paper and starting over. I wouldn't focus too much on the overall length to begin with, just see where it ends up once you have the accommodation space you want accounted for.

    The entire time your doing the above, try to keep the heavy parts of the boat such as tankage, engine, galley and bathrooms, nearest the longitudinal center of the design rather than at the extremities. This will develop a boat with best possible pitching characteristics. You will need good sea manners if you are to maintain the higher speeds your looking for in a seaway or comfort will slow you down long before the fuel consumption does.

    I like your idea, I had a similar one myself. The extraordinary length which results from designs like this is mostly a headache for berthing. If your not going to park her in a marina or similar, then the length is not such an issue. In fact the more length the better once your on the water IMHO - only limited by your budget really.
     
  3. longcours62
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    longcours62 Junior Member

    The problem if you are like me

    Ok , we make a list of what we need in storage, volume of arrangement, size of deck saloon, length of cabin, volume of tankage, etc etc
    We make a viable drawing for our use, 2 or 3 different volume and models of roof (just wheelhouse, wheelhouse and deck saloon under the same roof, or roof for wheelhouse on a roof for the deck saloon)
    and finally we make "a drawing " where we can fit our potential arrangements ... the result is below (please this drawing is just for the volume and mains characteristics !! As you can see we know nothing about efficient hull lines :D!!)
    Finally the displacement of the main hull is 15,6T + around 2X0,45 t

    :confused: I need to find 3/4 m3 somewhere:p
     

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    Last edited: Dec 6, 2014
  4. groper
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    groper Senior Member

    The hull lines are not important at this stage, efficiency will take care of itself provided you have minimum weight, on maximum waterline length. It's that simple.

    I also have no idea where you come up with 15-16t. How do you know how much displacement she will sink if you don't know what she weighs yet?!

    If you want efficiency, you must keep her light weight. This may mean things like smaller water tanks with a water maker instead of large tanks etc. There is no free lunch, only compromises...
     
  5. longcours62
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    longcours62 Junior Member

    For the weight estimate

    We start from our actual boat already built and we make a list :
    - minus 1,3 t because one engine only(engine , bedding, filters , day tanks, shaft, sterntube, exhaust, etc),
    - minus 3 t of ballast don't need anymore (Power trimaran)
    - minus 2,3t for aluminium (near same developed surface , but smaller thickness)
    - minus 2,43 t of wood, plywood (les arrangement and lighter material)
    - minus 0,3 T water tanks smaller from 0,7 to 0,4 m3
    - minus 0,25 T less tools
    - minus 0,25 T less books, magazines
    - minus 0,25t smaller chain and anchor (lighter boat)
    - minus 0,10t smaller rope
    - minus 2,675t of diesel tanks, same range with better (hopped) efficiency

    etc

    Finally we arrive at around 20t, we can't going less.
    And the 15,6t was given by ...the computer for the volume of this curious hull:p plus the volume of small lateral hulls (sponson ?) may be 2 x 0,64 m3)

    It is why I wrote : I need to find 3m3 somewhere:) :?:
     
  6. groper
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    groper Senior Member

    You don't need ballast! It's a trimaran, you don't have a stability problem.....

    If you are looking for help, you need to try and forget a lot of your preconceived ideas. Otherwise you will only get what you would without any help...
     
  7. surfbus
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    surfbus justin

    woow ,,,my thread got hijacked by froggie and now everyone is bailing!

    come back ..help!!!
     
  8. surfbus
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    surfbus justin

    llongcours62 just go longer to get your volume !!!

    everyones doing it
     
  9. surfbus
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    surfbus justin

    Leo, how about those sponsons for the sumatra surf bus?
     
  10. groper
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    groper Senior Member

    Or he could carry more of the displacement in the sponsons... or he could build it from lighter materials, or he could.... or .... or.... the list is endless.

    You have to be prepared to do alot of your own homework. Its not feasible that you can come onto an online forum and expect someone to design a boat for you free of charge, alot of work and expertise goes into a new design if it is done properly.

    Have a look at Leo`s program called Michlet. Its not very user friendly, but if you can get your head around it and learn what parameters to put into it, it will give you an idea of what to expect from changing the ama displacements vs main hull displacement, and the location and lengths of the hulls also. For best seakeeping character, i beleive the small amas should be placed quite aft similar to the "earthrace" trimaran design. This seems to give the best response in a seaway for numberous reasons which you can study up on should you find the motivation to keep going...
     
  11. surfbus
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    surfbus justin

    roger that grouper,, you guys have been a lot of help already. I'm trying to juggle family , home improvements, and a business so my timeline is not going to make this happen overnight,,but on my free time I can't help myself from figuring out more of my u.s.s. enterprise.

    Once i do some more homework on concept who do you think I should commission to do the proper engineering work?
     
  12. longcours62
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    longcours62 Junior Member

    May miss understood my poor English !

    Above it is exactly what (I thinks :confused:) I wrotte :"- minus 3 t of ballast don't need anymore (Power trimaran)":confused:
     
  13. groper
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    groper Senior Member

    Why not contact the people who already have the runs on the board?

    Nigel irens - " ilan voyager" might be close to what your after?
    John shuttleworth - designer of "adastra" super yacht power tri with high DLR.
    Craig loomes, lomocean, designer of "ady Gil" world record circumnavigation of the globe in a powered vessel, power trimaran.

    I doubt any of these guys are going to be cheap, so prepare yourself...
     
  14. surfbus
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    surfbus justin

    ya...everybody will think I'm made of gold......maybe we should split the cost longcours62?
     

  15. JRD
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    JRD Senior Member

    Geez we have never met anyone here who isn't made of gold before.... :D

    You will read it 100 times here, buying a good plan will cost you a good deal less than building from an average one.... if you want a quality result.

    You may find that the plans for an existing design are a pretty small fraction of the eventual build cost even if you do it yourself.
     
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