Another question about Hobby Kat

Discussion in 'Multihulls' started by bjhbjh, Jul 31, 2007.

  1. bjhbjh
    Joined: Jul 2007
    Posts: 13
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    Location: Uxbridge Ontario Canada

    bjhbjh Junior Member

    Hi again,

    I have been looking at the Hobby Kat plans some more and I have another question for you experts.

    Looking at the frame outlines on this page, I don't see how to establish the lateral (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?

    Also it appears to me that from RIB/Frame A to RIB/Frame 1 there is a latteral offset difference from 1 7/8" right of centre to 1" left of centre over the course of 22" of keel lenght. Does this seem extreme to anyone else?

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

    Lenny25 Junior Member

    Good question. I have the same problem, has anyone discovered a solution. Brian did you finish making this boat?

    I'm not an expert, but from what i can see on the plans: The offset of the tip of rib A and the tip of Rib 1 (center of the keel) is irrelevant. Since rib A is only a floating rib (half rib), the keel does not touch rib A at all. However there is a small lateral offset of the inside of the hull from the center line inwards - from 6 3/4" to 5 7/8". The outside of the hull remains almost exactly parallel to the center line over this section of the hull (from rib 2 to rib A). So the starboard side(inside) of the hull curves in by 3/4 of an inch over 22 (not too extreme) while the port side remains almost parallel to the centerline. From the transom to rib 2 both sides of the hull widen equally on either side of the center line. The keel however starts on the centerline at the transom and curves slowly to the left of the centerline the whole length of the hull.

    Now as far as where it stems from on the Jig- well your guess is as good as mine. In fact thats what is suspect will have to happen. One might have to simply line up all the ribs according to their centerline of the jig, fasten the keel to the ribs and transom and GUESS where to nail the stem of the keel!
  3. Lenny25
    Joined: Mar 2009
    Posts: 11
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    Location: Cape Town, South Africa

    Lenny25 Junior Member

    Whoops, i see this question was moved to another thread./
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