Design pressures on multihull hull-skin

Discussion in 'Multihulls' started by simon, Nov 19, 2009.

  1. simon
    Joined: May 2002
    Posts: 101
    Likes: 3, Points: 18, Legacy Rep: 70

    simon Senior Member

    Thanks very much for all the advices Phil.

    I will put some stringers and a frame into place to reduce the panel-span. Is it advisable to build a stringer the same way you explained to build a frame? With foam-core which is laminated onto the skin? Do the stringer need to be aligned with the stringers that end on the other side of the bulkhead?

    I am very grateful for your support. I will soon come up with another issue that I would like to solve. The escape hatch problem is almost solved, the fairing, painting and trying to integrate the old hatches, is left over.



  2. catsketcher
    Joined: Mar 2006
    Posts: 1,315
    Likes: 165, Points: 63, Legacy Rep: 790
    Location: Australia

    catsketcher Senior Member

    Shelves are easier

    Gday Simon

    The only thing against frames is that they can be harder to make due to the curvature of the hull in the vertical plane. Also the very curvature means that the hull should be pretty stiff in the curved area.

    How you build the re-inforcing is up to you and the circumstances. I would urge you to think carefully and try to incorporate the new structures usefully somehow. The interior furniture inside a modern multi is usually vital structurally.

    In a crashbox you can go big and use large section of ply or duflex on edge. These will be very stiff. In an accomodation area you may be able to incorporate a shelf to stand on getting up to a bunk so you make a 200mm wide shelf or you may want to hide vertical reinforcing so you go lower but in foam.

    I would go deep for a stringer (that is why I call it a shelf) as it usually has larger spans than a frame. It would be 5 times easier to make as the rate of curvature is much lower. Frames can be buggers to make in situ. As for ending it - there is no huge need to make shelves meet if the frame is bulky enough. If the frame isn't then it needs sistering. This is where you strengthen a frame with another although in a composite boat you would just glass the frame.

    Just remember to put a tape under the shelf or frame and use a nice 50mm spatula ground round for the coves. Leave a slight gap between the frame and hull and fill this with epoxy - don't push the shelf hard against the hull.


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