Uneven Fiberglass Stringers for Plywood Boats

Discussion in 'Boat Design' started by DouglasEagleson, Sep 29, 2016.

  1. PAR
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    PAR Yacht Designer/Builder

    I've seen preformed "U" shaped 'glass stringers fitted previously, though usually as localized reinforcement, if scaled properly, they could be employed along the chines. They're tabbed in, just like anything else, though a lot of bother, unless you have a need for a bunch of specific height/width, thickness pieces.
     
  2. W9GFO
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    W9GFO Senior Member

    I disagree with nearly every word here. Copper, or any type of nail, would not add any strength to a fiberglass seam. Nails can indeed be used for plywood. Bolts have no place in taped seams. Taping can add a lot of strength and lastly, a wooden chine is not the only correct method.

    It is unusual that I find a block of text filled with so much that I disagree with. What am I missing here?
     
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  3. SukiSolo
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    SukiSolo Senior Member

    There are plenty of hollow glass moulded 'chines' used as stiffeners on lots of boats such as 470s'. Almost all are all glass though. On a single or multichined wooden boat there's no reason to use them at all IMHO. As for using copper nails into a solid glass chine well that is asking for some real problems.

    Better to use an epoxy fillet to replace the chine stringer. You don't even need to glass the outside, but best to epoxy sheath it anyway. Personally I prefer to laminate wooden stringers as internals IF you want more strength ie stiffness along the chine itself. Lamination is to get the stress out of the 3D curvature of the stringer. You can bend ie steam some stuff to do this. These work well for planing to shape and will stay put if the frame spacing is reasonable, then all you need to do is glue the planking on and plane back.

    Those old copper nails are a throwback to the 40's and 50's when adhesives were not as good and they 'solved' clamping problems. A decent number of F clamps or similar, even tape can hold a lot in place where stress is minimised. Also you can use screws to hold a panel, which are later removed and the
    holes filled with epoxy and filler. Much better integrity using these methods.
     
  4. DouglasEagleson
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    DouglasEagleson Junior Member

    My concept is a simple one. There was aa clear statement defining class of chine mating. I never claimed novelty. In my version a dingy must be strong enough to be towed as a possible life boat. 1/2 inch fiberglass corners is as strong as the first layers bonding. So adding thickness requires fasteners. Nails or bolts with pilot holes.

    Also consider a need for drop tests of dinghies. In general terms it means a 20 foot capacity to not breakup in. Just consider the need for a storm capable towing stanchions, also.

    I just cut out the bottom plywood panels for my 14 foot tug boat. I will demonstrate it there. It is a triangle/square design. Meaning all panels are either triangle or squares.
     
  5. SamSam
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    SamSam Senior Member

    It sounds kind of like a Stealth craft, it ought to be interesting.
     
  6. gonzo
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    gonzo Senior Member

    There is no drop test for dinghies that I know of. However, you could write one up. In WWII they would drop landing craft from more than twenty feet and they didn't break. They were built of plywood with wooden chines.
     
  7. rwatson
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    rwatson Senior Member

    It would be interesting to see the engineering calculations for all this "strength required" stuff.
     
  8. Commuter Boats
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    Commuter Boats Commuter Boats

    Is this a Bolger design or something that you've worked up?
    Sounds very Bolger like which is not intended as criticism, I think the gentleman was a genius which isn't to say that all of his designs bore that out.
    Gerald
     
  9. DouglasEagleson
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    DouglasEagleson Junior Member

    Doug's Tug Inner Hull

    My fios stinks I will follow up. this posting
     

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  10. DouglasEagleson
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    DouglasEagleson Junior Member

    Here is a better diagram of the bilge part of my tug boats. It can also be added to contemporary flat bottom tug boats for use as a inboard engine well.

    The only hard part is sizing the main frame to panel angle.
     

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  11. DouglasEagleson
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    DouglasEagleson Junior Member

    screwed up thinking wise, edge c is cut to a right angle with the flat plane. NOt perpendicular.
     
  12. DouglasEagleson
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    DouglasEagleson Junior Member

    I got to thinking about clarity of communication. There is a likely confounding of sizes of the bilge panels. So to get exact fitting a fitting procedure is the best avenue of ensuring triangle sizes. First cut the aft panels and mount them on a set of temporary frames. The short seam angle cut will ensure a good rear hull. now use it as a reference point.

    Next set up the bow temporary frames and be ready to make a complex cut triangle. This means cut the square panel to two triangles. Set the top main seam along the line, x to bow point, this is the middle seam. Now use a template to size these front triangles to the main, rear frame defined frame. The short seam and the long seam may be needing manual definition.
     
  13. rwatson
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    rwatson Senior Member

    In the spirit of not wanting to see a lot of expensive plywood wasted, have you had the hydrodynamic calculations done ?

    As far as performance as any kind of boat, well, I recommend you don't take it far from shore.

    You don't have to worry about towing dinghy strength at least. You wont be going anywhere with any kind of heavy weather.
     

  14. DouglasEagleson
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    DouglasEagleson Junior Member

    when I get the prototype done I will report hull speeds using a 4.5 hp Johnson outboard.

    It will be a basic temporary low strength prototype. Almost a one use hull.
     
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