Keel Fore/Aft locations

Discussion in 'Sailboats' started by NPH, Oct 27, 2009.

  1. NPH
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    NPH Junior Member

    Hi all.

    Does anyone here know, what the effects of moving the keel's COE, from directly underneath, farther aft, or even forward of the hull's COE, do to handling?

    Also, the same thing, but with the rig's COE and the keel's COE, moving together, closer to or farther aft of the hull's COE.

    One question on my mind is, do these movements in location, affect how the boat turns. Such as, if the keel is close or underneath the hull's COE, will the boat turn easy? Or, if the keel is Farther aft, will the boat be harder to turn, because with the keel behind the hull's COE, the boat acts like it's pulling something? Which would probably make the boat track straighter I'm guessing????
     
  2. lewisboats
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    lewisboats Obsessed Member

    What kind of keel? Fin keels and rudders make the hull's COE much less of a factor mainly because the hulls are usually relatively shallow compared to the old long keels or full keels. The fins generate much more lift for their size because of the foil shape and the aspect ratio. A long keel is generally molded in as part of the hull's shape and the whole thing is used when calculating the CLR but generally only the foils and perhaps a skeg will be considered in modern hulls unless they have an unusual configuration.
     
  3. NPH
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    NPH Junior Member

    Long, blade type keels, like on IOM & Marblehead hobby boats.

    I figure on plumb-line-ing the COE of the bulb, through the center of the keel at it's COE, but would like some advice on where the plum-line should start.

    Only as a ballpark on a winter-build. I'm going to make multiple locations on the hull & deck of a proto, to see for myself what the changes do, but that's a while away (spring-time).
     
  4. phum
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    phum Junior Member

    On the type of boats you speak of (models) the centre of bouyancy is the controlling factor. The lead/ballast (probably 80+% of displacement) must be directly below the CofB or the trim will be affected.
    Peter
     
  5. NPH
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    NPH Junior Member

    Can this "Trim", be compensated for with a corresponding movement with the rig?

    Say, moving the keel back will make it lee-helm, but then moving the rig back stops that, but now the whole COE-balance between the rig & keel, are behind the hull's CLR vs. directly centered with the hull's CLR vs. maybe ahead of it? :confused: What are the affects?

    I think I'm thinking about it to much. I'll just have to wait until sea-trials. As long away as it may be. :(
     
  6. phum
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    phum Junior Member

    Trim I describe as for and aft attitude in the water.
    If you move the keel/ballast forward the boat will be bow down and with aft movement the stern will imerse. Whatever you do with the rig will have little affect on the trim. Fins can and have been raked but this generally only introduces another problem of fin twist when the boat heels.
    Peter
     
  7. NPH
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    NPH Junior Member

    I see.

    What about if there was no ballast bulb, such as a multi-hull. How then, would my above ramblings regarding the appendage/ rig movement, affect them :?:
     
  8. phum
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    phum Junior Member

    Multi hulls are a different breed, I have no experience with them. In your previous posts you mentioned Marbleheads etc. and ballast bulb and I assumed you were speaking of monohulls, sorry.
    Peter
     

  9. NPH
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    NPH Junior Member

    I should have been more clearer. I used those mono referances, to give an idea of the keel shape ie. long blade-like.
     
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