LARS design question

Discussion in 'Multihulls' started by kim s, Jun 16, 2011.

  1. kim s
    Joined: Apr 2009
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    kim s Junior Member

    Can any one point me in the right direction please.

    my technical credentials?------none---official numpty.. only thing is I have rebuilt a wreck and she is on the water and sailing)

    How do you design an aysemetric keel?

    Do you make a complet foil shape (NACA profile) and slice it down the thickness and bolt on 1 each side or is the profile different. ( I know it would not be strong enough but I cant explain it any other way)

    my Lively 28 has 2 steel plates bent into foil shapes but there is a huge amount of noise and turbulance so they must be dragging.
    I do have the problem that the amas are to low and so its difficult to get the windward keel completly clear and so the keels fight each other.
    but I can see the turblance in the water so they must be badly made/designed
    dagger board will be the way to go but not this year. I will need to strenghten the hulls to take the added pressures so winter job.

    If any one can help

    Kim S
     
  2. kim s
    Joined: Apr 2009
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    Location: essex, uk

    kim s Junior Member

    lar keels

    Ah Ha-----got you all stumped¬!!!!!

    no--- is it that Ive asked or not explained the problem I have got, properly

    did say I was a numpty.

    From what I can find out its almost -----make it up by eye (stick out thumb, close one eye, suck in through teeth, tilt head on one side------"yeah that should do it":D:D:D:D

    or mabye should have posted this on the general design part of the forum.

    if any moderator thinks it should be moved, please do

    thanks

    Kim
     
  3. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Is a simple enough question. Yet:

    Is not related to the question.

    There is a disconnect between your question and what you "think" is a problem. And the assumption is that you assume having an asymmetric keel will solve a problem, which has yet to be determined if one really exists.

    Hence how do you know what the problem is without proper investigation?
     
  4. cavalier mk2
    Joined: Mar 2010
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    cavalier mk2 Senior Member

    Hi Kim S, While I'm horrified at the thought of a multihull with steel plate keels I have a suggestion. On the concave surface attach a filler piece (wood or....) to make it flat and see if it improves things. Do one side at a time as you investigate for comparison. If you lose the steel plate keels the amas might not ride so low......
     
  5. kim s
    Joined: Apr 2009
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    kim s Junior Member

    I am not assuming that having them will solve the problem.---I have them already??? whatI am asking for is info to see if I can determin they are correct or correct ish , if they are there are there abouts, then I will know wether they are a problem.
    As I have stated earlier, I am only going on what I can observe and from my lack of any technical qualifications in hydro dynamics. thats why I need to ask for help or ideas.

    Cavelier,
    I am now beining to understand your horror!!!!
    I have been thinking about this now for a few daysand I think that your right in Filling the concave surface in.
    I am thinking about making temporary flat plywood keels the same shape (not foil shape though) and trying them.
    I suppose I was hoping for some one to say ----" arrgh yes go to this site and all is explained" It looks like as you say, try something and see if it improves is the way forward (but maybe a little bit more sideward:):)

    and just thinking about what you said, I suppose losing the weight would also be huge benifit not only to the overall weight, but the extra inch of freeboard. hmmmmmm right, off to the garage we go.
    thanks
    Kim
     
  6. cavalier mk2
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    cavalier mk2 Senior Member

    No problem Kim. If it was my boat I'd make the new keels a symmetrical section say NACA10-12. or thereabouts. You can find offsets for the sections on the internet if you look around. I say symmetrical because offwind and in light airs you'll often have both keels in the water at the same time. If you make them of wood it is pretty easy to play with the shapes.
     
  7. Gary Baigent
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    Gary Baigent Senior Member

    If you're determined to having fixed asymmetric keels (fighting one another) then the only answer is to have them lifting like daggerboards - and lift the windward one so that the correctly shaped leeward asymmetric does its best job. Otherwise, since I know you won't do that (make them movable) then make them symmetrical, like Cav says.
     
  8. kim s
    Joined: Apr 2009
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    kim s Junior Member

    Cheers Guys, I had got into a fixed idea of asymmetric keels or just flat shapeless plates. doh!!!told you I was offically numpty:p

    Calvalier, Making them Naca10-12 was the number I was playing with. Naca actually have a program that you down load and put in the profile and chord depth and it give you the offsetts.
    I suppose start off at 12 or bigger and try then take them down to play with.them. 12 seems to be the general start off things.

    Gary, I am not determined to keep fixed keels, when the boat comes out the water for the winter then I am going to look at dagger boards,

    this whole thing started really because I could not find info on asymmetric keel design and wanted to see if they where a problem due to incorrect build. I REALLY want dagger boards but that will be major surgery on the Amas.. not this summer:)

    any way big thanks to all you have pointed me in the right direction. I am going to take them off , make some temporary fixing system so I can just unbolt and try different profiles.

    A floating test bed..excellent

    cheers once again for your patience

    Kim
     
  9. cavalier mk2
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    cavalier mk2 Senior Member

    Cheers to you Kim, now that you're losing the ballast we don't have to call you a bletherskate, or say you sail one!
     

  10. kim s
    Joined: Apr 2009
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    Location: essex, uk

    kim s Junior Member

    :D:D:D:D:D

    Kim
     
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