cold molding construction

Discussion in 'Boat Design' started by adriano, Sep 29, 2013.

  1. PAR
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    PAR Yacht Designer/Builder

    If that's the case Adriano, than a reasonable argument can be made for both materials in some applications and build methods.
     
  2. adriano
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    adriano Senior Member

    Hi Paul,
    OK thanks, It seems to be more complicated matter than I thought.
    You may address me to some books or related literature about details on plywood use in boat building?
    I would appreciate if you could.
    Adriano
     
  3. SukiSolo
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    SukiSolo Senior Member

    Best book on Cold Moulding and Strip Plank Construction is by Ian Nicolson. Regrettably someone 'borrowed' my copy and never returned it. Worth having in your library though if these techniques will ever be of use to you. ISBN 0-7136-3524-X

    There is quite a history of good plywood manufacture from Fairey Marine using autoclave baking and later vacuum bag technology, for curved shapes. On pure sheet ply building, I don't have any A* recommendations. The only thing when designing chine hulls is to make sure you can get the curvature without excess distortion. The panels have to be developable, however some CAD programs will tell you you can't when you can and vice versa. Thats where experience, models and a lateral thinking approach can come in handy!

    PAR, nice work on your craft, really like the big support framing for the outboard area on your 'fishing' craft. Please take good note of PAR's details, Adriano, he has properly addressed and thought about many issues that you are raising.
     
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  4. PAR
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    PAR Yacht Designer/Builder

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    I wouldn't necessarily call this the best treatment on the subject (getting a bit dated and some advances have been made, since being published 15 years ago), but it's certainly a good reference to have in your library. The latest edition (5th) of the Gougeon brothers BoatBuilding manual also is a good one to own (free PDF download at westsystem.com). A good bit of information is available online too.

    Thanks SukiSolo, though Adriano and I have some history together off site. He knows I don't pull punches. If you need Ian's book, I've found a few for less than $50 bucks (used), though new ones are expensive ($100 or more).

    For your needs Adriano, a solid wood approach will not let you down, especially if laminated to gain the most of fiber orientation. I have a variation of the Lord method (I think we've discussed this previously) that does use plywood, nearly exclusively, in the structure of a strip planked build (strips are sheathed solid wood). This particular method is for very light builds, so wouldn't be considered for a cruiser or work boat or other hefty or heavy duty service. Simply put, it can be a complicated issue, but only on designs where you're trying to take best advantage of weight, stiffness, strength, etc. In most applications, you'll prefer to employ solid longitudinal members, unless a laminate is bearing a high percentage of the load.
     
  5. DCockey
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    DCockey Senior Member

    Renn Tolman recommends LVL (Laminated Veneer Lumber) beams as material for the stringers in his designs. LVL is essentially thick plywood with the grain in all plies oriented in the same direction along the length of the beam. In North America beams are available in thicknesses of 1 3/4", 3 1/2" and 7", widths up to 24" and lengths up to 24 feet. Larger dimensions and longer lengths may be available.

    LVL should not be confused with PSL or LSL.
     
  6. PAR
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    PAR Yacht Designer/Builder

    LVL's are a way to go, though heavy, quite stiff. Mostly seen in larger composite or taped seam builds. Tolman's stuff is way over the top in regard to scantlings, so an LVL makes sense for him.

    Actually there are a few choices with engineered lumber; LVL (laminated veneers), LSL (laminated strand), APB and PSL.

    APB is basically laminated 2x4's or 2x6's in a flat stack. I've seen these but have no experience with them.

    Parallam (PSL) is a modified LVL with longer and thinner strands with more organized arrangement.

    Last is Timberstrand (LSL) which is a strand product too, but they use different species effectively in compression and tension pathways. Not as tough or strong as some of the other choices, but still very stiff and considerably cheaper.

    If you're going to "play" with engineered lumbers and beams, the APA as well as several other sources can provide the physical attributes, so you can size them properly.

    Unless building a hefty powerboat, these aren't products I would use, but if you happen to have a length of Parallam hanging around the shop with nothing to do, it could make a nice (if heavy) keel or stringer.
     
  7. adriano
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    adriano Senior Member

    Apprecite all yr comments!
    Jan Nicholsons' book as well John Guzzwell's are part of my boat library for long time.
    Well my issue is not of course about cold molding contruction im general but ruther adressed only to a specific matter by using vertical plywood as hog extending out of the planking (keel) and eventually its limitation. My personal feel is that this might be a too vulnerable. It might be fine with rowing boats but definitely at least on power boat there should be some limitation in using it!
    Personally I agree with it limited to hog (internal keel) but not as keel.
    Thanks
    Adriano
     
  8. PAR
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    PAR Yacht Designer/Builder

    If I used plywood, it would not be used externally, but only internally. Externally, it's just not the best choice, as you'll never get the end grain fully protected, without additional efforts. Internally, this is less an issue, as one end can be buried in a fillet, with the other capped with laminate or other treatment.
     

  9. adriano
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    adriano Senior Member

    Yes Paul,
    that's what I've in mind too.
    Adriano
     
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