H/K Question repost

Discussion in 'Boatbuilding' started by bjhbjh, Aug 2, 2007.

  1. bjhbjh
    Joined: Jul 2007
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    Location: Uxbridge Ontario Canada

    bjhbjh Junior Member

    Hi,

    I posted this question about Hobby Kat the other day in the design/multihulls forum, but as it has yet to garner any responses, it occurred to me that perhaps it was inappropriate there, being a fabrication not a design question. Hopefully it is more germane to this forum and so I am reposting it here.

    First off, has anyone here ever built this craft from these plans? I'd love to hear the voice of direct experience. Surely in all the years since its publication, someone must have attempted it.

    I have been looking at the Hobby Kat plans with thoughts of building same as my first boat project. I am reasonably comfortable that I understand the plans but I have a question for you experts regarding where to locate the keel latterally at the stem. The plans don't show a view from above.

    Looking at the frame outlines on this page, I don't see how to establish the lateral (IE port / starbord) starting point for the keel centre line at the stem. Where do I centre the keel at the stem when jigging this up?

    Surely, I need to know this as the prow keel bend is the step 1 of the process.

    I would naturally have put the latteral centre line of the keel on the centre line of the jig BUT I see, looking at the frame/rib outlines that by rib/frame A it has to be right of centre by 1 7/8" and by rib/frame 1 it has to be way left of centre by an inch. Can this be right? (Is the frame/rib A of the other hull shown in error? I don't think so judging by the position and sizes of the batten notches.)

    I read in the text that the hulls have an airplane wing shape to them to help right the craft when heeled, and I surmise that the curvature of the keel obvious from the different offsets from frame piece to frame piece is there to form this wing shape but I don't see anywhere that specifies where the latteral startpoint for the keel's centre line should be. Have I missed something obvious?


    Ok and while I am at it, if the wing shape is righting the craft when heeled, doesn't its stand to reason that these forces are acting against one another when both hulls are in the water? Won't that create drag? Or do the differenet angled surfaces on the inner hull sides lessen this effect until one or the other hull is submerged deeper by the forces heeling the boat?

    Hope this is clear. Thanks for your time and efforts.

    Best regards,

    Brian H.
     
  2. alan white
    Joined: Mar 2007
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    Location: maine

    alan white Senior Member

    Bear in mind, any heeledl boat presents a curved longitudinal shape to the direction it moves.
    Your plans show station molds with offsets from the vertical mold centerlines to the curved keel centerline, except forward of the formost frame. You have no body plan however, and those offsets would have shown the stem/keel line on the top view. The assumption is that the mold centerline is established by the lateral position of the stem-at-deck in the first place.
    Lacking any conflicting information, the deck at the sheer should fair forward into the centerline where the deck meets the stem. It only makes sense that the hulls are drawn based on a centerline from stern center to bow center. Anything else would not make sense.

    Alan
     
  3. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    On the page of frames/ribs, in the side view at the bottom, it shows only that T, 1, 2, 3 + 4 go all the way to the keel. The frame/rib A doesn't. It only goes part way and only supports the side battens.

    I'm not quite sure what you're talking about in the rest of the post, but in this plate...
    http://www.svensons.com/boat/?f=SailBoats/Hobby_Kat/Hobby_Kat_03.jpg
    if you hold a straight edge to the keel in the 'top view', there is a definite curve to the keel, if that helps.
     
  4. bjhbjh
    Joined: Jul 2007
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    Location: Uxbridge Ontario Canada

    bjhbjh Junior Member

    Thanks for your thoughts.

    I think you are correct and my original inclination was in line with this.

    I drew out a scaled plan view of the keel from stem to stern based on this assumption.

    It goes through an 'S' bend with the most extreme slope happening over just 22" of the 14' hull. Does this not seem disquieting?

    Thanks,

    Brian H.
     
  5. bjhbjh
    Joined: Jul 2007
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    Location: Uxbridge Ontario Canada

    bjhbjh Junior Member

    By golly you're right!

    You're right!

    That little triangle shown at the top looks like keel. It had me fooled till you pointed this out!

    Thanks a million, I feel SO much better now cause it all makes sense!

    I'll keep you posted of my progress.

    Thanks again!

    Brian H.
     
  6. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    I also edited and added this to the above post...

    "I'm not quite sure what you're talking about in the rest of the post, but in this plate...
    http://www.svensons.com/boat/?f=Sail...bby_Kat_03.jpg
    if you hold a straight edge to the keel in the 'top view', there is a definite curve to the keel, if that helps."
     
  7. bjhbjh
    Joined: Jul 2007
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    Location: Uxbridge Ontario Canada

    bjhbjh Junior Member

    Revised keel plan view

    Revised my plan view of the keel in accord with SamSam's advice.

    These lines are much more pleasing indeed!



    Thanks again!

    Brian H.
     

  8. Lenny25
    Joined: Mar 2009
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    Location: Cape Town, South Africa

    Lenny25 Junior Member

    Hey Brian

    How did the build go? Does anyone know of someone who has built this boat?
     
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