Long Keel Shaping

Discussion in 'Sailboats' started by Richard Gordon, Feb 18, 2021.

  1. Richard Gordon
    Joined: Feb 2021
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    Location: Connecticut

    Richard Gordon New Member

    Hello,
    I am trying to shape a long keel for a ketch rigged sail boat. I made hull and want to add a smooth long keel with the use of Rhino. After trouble shooting for a couple of hours I have not been able to figure out a good way to shape a smooth long keel. Please help

    upload_2021-2-18_10-34-0.png
    Here is a picture of my hull with my attempt of making a long keel.
     
  2. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    Try to create it with one or more surfaces, independent from those of the hull.
     
  3. wet feet
    Joined: Nov 2004
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    Location: East Anglia,England

    wet feet Senior Member

    That doesn't look like a keel outline that would win you many friends in any boatyard that has to haul or store the boat.First question;how much 3D modelling have you done?Second;do you intend to hang a rudder aft of the keel or as an appendage of the trailing edge?

    The basic process shouldn't be much more complicated than establishing a leading edge and trailing edge on centreline and extending inside the hull a little-that way you can use the hull surface to trim the keel.Assuming you plan to use a foil section you just import (or draw) the section you wish to use such that it contacts the centrelines you just established and then use a 2 rail sweep to create the keel surfaces.Trim using the hull surfaces as a cutting entity and if you need to establish a volume for weight calculations you umay need to duplicate the hull surface and trim to the outer shape and then join with the other surfaces before you make a solid and ask for the volume.
     
  4. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    I know nothing about Rhino, but when it comes to long keels I have a particular fondness for Chuck Paine's Expannie design - here are some of her drawings.
    If you can model something like this in Rhino, I think you will have a very nice hull form.

    Expannie side view.jpg

    Expannie lines plan.jpg

    Expannie 3-D view.jpg
     
  5. rangebowdrie
    Joined: Nov 2009
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    Location: Oregon

    rangebowdrie Junior Member

    That is a nice shape,, and it appears that he, (correctly,) used a parabolic shape for the leading edge. I would like to see a bit more "filling in" of the large opening forward of the rudder that's around the prop, but that's just me,, and his design does have advantages.
    He has a good eye, I always liked his little "Annie" design.
     
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  6. wet feet
    Joined: Nov 2004
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    Location: East Anglia,England

    wet feet Senior Member

    The Paine design shows characteristics that experience brings.A keel that the boat can stand on,either for scrubbing or storage;a rudder that can be unshipped without digging a pit,the space to get the propellor off without having to unship the rudder and the connection of the rudder to the keel both confers strength and reduces the chance of ropes or rubbish catching the rudder.I don't doubt that the rest of the boat would work well if lessons were sought in how to do it right.
     
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  7. rangebowdrie
    Joined: Nov 2009
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    Location: Oregon

    rangebowdrie Junior Member

    Regarding the rudder; my first thought was that because of its high-aspect ratio it would be efficient, and more responsive to smaller inputs from the tiller.
    Mr. Paine has provided a raked and supported spade rudder of sorts, and he is using the same profile
    on his updated "ANNIE II" design.
    But it's his sheer-lines/profiles that grab me, his designs are "easy on the eyes".
     
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