Strip PLank Construction Details

Discussion in 'Boat Design' started by Mat-C, Sep 24, 2007.

  1. Mat-C
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    Mat-C Senior Member

    In "Elements of Boat Strength", in the chapter regarding the scantlings for strip planked construction, sheathed inside and out, Dave Gerr states that you can 'eliminate much of the interior structure'. The very next sentence says that interior structure should be sized according to the rules in chapter 5 (FRP internal structure)...:confused:
    Now my take on this is that you can eliminate the frames, just using bulkheads, unless there's a particularly large unsuported span. But what about the stringers? Obviously engine beds still need to be incorporated, but do these need to be full length? And are other stringers still necessary?
    Just what can you leave out and what must remain?

    "Decks and cabin structure should be sized according to those in chapter 9", he also says - referring to laid or ply decks, and ply cabin structure. What if this is to be strip planked as well...?
    The deck appears easy enough, you use the formula for a laid deck, but do you need to sheath inside as well as out?

    Lots of questions I know - sorry!
     
  2. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    In most cases you can skip stringers. Wooden strips have great longitudinal strength, but very little transverse strength. That's why you need glass both inside and outside.
     
  3. nero
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    nero Senior Member

    You might consider keeping the bilge stringer. This could help with impact from floating objects. It also acts as a cleat to install or lay floors on to.
     
  4. alan white
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    alan white Senior Member

    You definitely want to sheath inside and out any strip-planked panel used anywhere on the boat. In fact, in the case of the deck, the inside is more stressed than the outside. I would even consider hatcase sections of foam under deck spans, which will give tremendous stiffness for very little weight.
    These need only be 3/4" thick by 1 1/2" wide, for example, spaced according to athwartship span and common sense.

    A.
     
  5. Brands01
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    Brands01 Senior Member

    My take on the stringers was that Gerr recommends they remain - I think it is five full length on each side including the engine beds for that particular scantling rule. He recommends engine beds as long as reasonably possible, and definately full length for a fast planing hull.

    Any planked timber boat has longitudinal strength in the planking, but still has a number of stringers for additional strength. Therefore, a strip planked boat would be no different - it would most likely need longitudinal strength in excess of that provided by the planking alone.
     
  6. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    There is no easy answer to this.
    For exampel, take a traditional grp boat and build a simmilar with strip planking and biaxial glass on both sides. The wood wil make the new boat globally stiffer than the old one, and the glass will make it locally stiffer.
    Bilge stringers in traditional wooden boats are something else, in my opininon. There you have planking with practically no transverse strength.
    But of course, in most cases it's better to be safe than sorry :)
     
  7. Willallison
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    Willallison Senior Member

    Straight from the horses mouth:

     
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  8. alan white
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    alan white Senior Member

    Will, Dave Gerr passed away seven years ago.

    Alan
     
  9. Willallison
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    Willallison Senior Member

    :?: :?: :?:
    Err... not the Dave Gerr who is the current head of Westlawn Institute, who signed my Westlawn graduation certificate, author of the book in question and the bloke I spoke to on the phone a couple of weeks back....
     
  10. alan white
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    alan white Senior Member

    No. I was just kidding. Either that or he really did pass away and has been replaced by a look-alike. I can't take credit for having known that, however.
    More than likely, he's still alive, and the one you met was the real him.
     
  11. Man Overboard
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    Man Overboard Tom Fugate

    Matt,
    You may be able to glean some info from this site:

    http://www.rutuonline.com/index.htm

    I'm not sure if John fox, <FCSdesign@compuserve.com> still runs his engineering firm, but he would have a more definitive answer for your particular design; for a fee of course.
     

  12. Mat-C
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    Mat-C Senior Member

    Thanks everyone - sorry for my delayed response - been away.
     
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