Strip planking machining, does section shape matter?

Discussion in 'Wooden Boat Building and Restoration' started by Corley, Oct 10, 2016.

  1. Corley
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    Corley epoxy coated

    I'm heading off to get a stack of WRC I purchased machined later this week and am curious about the pros and cons of square sided rectangular strip planks versus keeping more of the section and having angled sides on the strip. The majority of the sections are scotia and beading so I'm attempting to work out how to maximize the amount of material that is useable.

    They will be used in a composite strip plank that will be faired and painted so how it looks isn't important I'm thinking more whether the different shapes will have a bearing on how fair the strips might sit on the mold?
     
  2. upchurchmr
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    upchurchmr Senior Member

    Narrower strips will sit on the mold more fair.

    Bead and cove strips made from a rectangluar beginning strip are automatically narrower.
    For instance you can use 3/4 x 1/4 rectangular strips or you can then put a bead and cove on the strip which wastes 1/4" in the finished product. It will act like a 1/2 x 1/4 strip. But you actually wasted the 1/4" that got cut off and overlapped.

    One thing you can do is to use rectangular strips, but don't chamfer the edges to make a perfect joint. You can glue the joints by spreading epoxy over the lengthwise joints after the entire part is stripped on the mold. This works just fine if you are painting, the high curvature areas show the open gap as a dark line if you are doing natural wood finish. If you have lots of curvature you might need to mix up some bog to get the gaps filled, and if there are flat sections there might not be very much glue in the joint.
    This method can be much faster, but you then have to grind/ sand the epoxy joint areas to fair the boat. Fairing wood is much easier than epoxy/ wood over large areas.
    You have to decide which is quicker - fitting strip to strip, or sanding the epoxy.

    Hope I didn't miss something - what is scotia and beading? I assumed that was bead and cove. And I didn't really understand "having angled sides on the strip". If I understand correctly, I suggest making all the strips exactly the same - square edged, and the same dimensions. It gets very labor intensive to custom fit non standard strips. And you will have lots of fairing if you leave one side of the strips rough cut.
     
  3. Corley
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    Corley epoxy coated

    Hi Marc, Beading and scotia is a strip used to hide the edges of floating floors it's generally good quality, clear timber.

    I've strip planked before but only with rectangular sections. I was thinking of getting the edges machined on an angle to cut less of the material to waste. There would not be any negative effects structurally but I'm curious if the different thickness of the angled parts may cause the strips to lay less fair.
     
  4. upchurchmr
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    upchurchmr Senior Member

    I don't know how much of an angle you were thinking of, but if you are going to use typical wood glue (not epoxy) between the strips, the wood glue does not cure up hard unless the glue line is small.
    So too much angle for the curvature will reduce the strength.

    Is this for the fairings on the Kraken?
     
  5. Corley
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    Corley epoxy coated

    No, it's for the F40 trimaran composite beams. The strip planking is only 12mm thick so I don't think a slightly wider glue line should cause any problems in this case. Kurt Hughes even mentioned I could butt the planking together as long as it's bogged really well but I'd prefer to scarph as I think the strips will sit more fair across the forms. As he said the WRC does carry some of the loads but the carbon uni does most of the work. I'd like to keep the amount of fairing compound down as the weight really adds up over the whole surface area.

    The Kraken beam fairings are thin scarphed ply so no real challenges there.
     
  6. Barra
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    Barra Junior Member

    Corley, I find the engineering aspects of cedar composite construction fascinating. Can you post a sketch of the beam construction. I'm interested to know how two materials (Cedar/Carbon uni)with such different properties can "share" the loads.

    Information like this makes this forum so interesting.
     
  7. Corley
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    Corley epoxy coated

    It's pretty simple layup there is 300gsm carbon uni on the inside and outside of the cedar on the 0 degree axis sandwiching the strip plank, on the outside there is a glass triaxial that handles off axis loads which we could substitute to a carbon layup if the budget allows. On these beams the fairing itself acts as a structural component with plywood shear webs on the inside.

    Carbon doesn't seem as expensive as it used to be a good friend Andy who is building a Shuttleworth racing trimaran purchased 300gsm carbon uni for $10 USD a Square metre so the carbon option is looking more attractive given the relatively small surface areas.
     

  8. Barra
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    Barra Junior Member

    ^^Thnx
     
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