Guide to Strip planking construction?

Discussion in 'Wooden Boat Building and Restoration' started by Dhutch, Dec 29, 2012.

  1. redreuben
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    redreuben redreuben

    FAST STRIP PLANK.

    This business of convex concave strips applied one at a time may suit canoes and kayaks with a clear finish but for larger yachts it's nothing more than self flagellation and or a massive waste of expensive labour.
    For a 30ft Farr.
    When cutting your planks bevel one edge so that when they go up against each other on the flatter sections there is about a three mil gap, enough to screed in the glue. Where the bilge turns just use square planks. Make sure all planks are touching on the inside so the glue doesn't squeeze through though.
    Fasten to your mould frames with double headed nails as used in concrete formwork. Scarf ends may be held in place with strips of thin ply stapled across a few planks.
    Make up your screeding mix with 5 parts micro balloons to 3 parts Q cell into epoxy, just thick enough not to run out of your largest gaps.
    Screed into the gaps with a mortar trowel.
    The next day or asap pull the double headed nails and go over the hull roughly with a handplane followed by a large disc sander and then very course paper on a torture board. Don't be too pedantic just remove the glue runout and roughly round the planking. Fill any big holes with epoxy mix.
    Resin coat on a falling temperature.
    Glass on a falling temperature. Allow some cure time now if you like.
    Using the above mix but a bit stiffer apply the mix in vertical strips (gunnel to keel) with a 12mm x 12mm notched tiling trowel.
    As soon as the mix is sandable without clogging the paper sand the strips with a torture board until fair, don't sand to the glass, stop 2mm shy.
    I imagine the water flowing around the hull and sand at 45 degrees plus and minus.
    Clean out the grooves with a broom followed by vacuum or compressed clean air.
    Fill the remaining grooves, sand again to fair.
    Resin coat on a falling temperature.
    Apply Hi build epoxy and sand for topcoat.
    Very quick.
    However depending on how much glass has gone over the strips and or how much curing has been allowed this method can get print through on light laminates due to the glue lines.
    A good cure time in warm weather prior to sanding the Hi Build helps a lot.
     
  2. PAR
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    PAR Yacht Designer/Builder

    You adhesive mixture is woefully inadequate for this task. You've described a cosmetic fairing compound, not a structural adhesive. The only way this works is if the core is heavily sheathed on both sides, which also means you've probably used the wrong material for it, as it's just a floating bunch of twigs, not the longitudinally stiff stripped hull shell it should be.

    I do agree in that cove and bead strips is a waste of time and material. The rest of your post has good, solid and well established guides for working with goo and sheathings.
     
  3. redreuben
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    redreuben redreuben

    Par,
    Any adhesive that is stronger than the material it is bonding is a waste of money, that adhesive will hold while the cedar is torn to shreds. Been there done that.
    From memory the laminate was about an 850 or so Db cloth inside and out with multiple layers in way of the keel. Probably doesn't count.
    What do you call a foam core ? A floating bunch of plastic bubbles ?
     
  4. PAR
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    PAR Yacht Designer/Builder

    There are a number of strip plank methods and some are really cored composites, in which case the strips, just need good peel and compressive qualities. On a lot of strip planked builds, the strips serve a directional, structural function and the mixture used above wouldn't work in these builds, which was the point I was making. A fairing compound mixture (what's listed above) can't and shouldn't be confused with a structural adhesive mix in this type of build.
     
  5. redreuben
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    redreuben redreuben

    Well Par I'm not going to argue this to the death, I guess we'll have to agree to disagree :)
    I'd be interested to see what mix you would use if you could post that thanks.
    The thing is the mix we used is a bit more resin rich than a fairing mix as it only needs to fill a thin glue line, so adhesion is good and believe me it is strong enough to enhance the timbers (WRC) longitudinal strength.
    Using a structural adhesive is a nightmare to fair because it creates hard lines which blunt tools and cause hollows when sanded between the glue lines as the timber abrades at a more rapid rate than the glue line. Which makes glassing a nightmare and adds a far thicker fairing layer than would otherwise be necessary.
    While we used DB inside and out, the original spec was for DB external but only a uni at 90 degrees on the inside, so the designer had faith ! I think the builder decided on the DB internally because that was in stock.
    RR
     
  6. LP
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    LP Flying Boatman

    I too would be leery of your mix. Both fillers are light duty products used for fairing and filling. I plan to use a similar process and will have some glass bubbles, but also colloidal silica and some wood flour for color. I will be testing various mixtures to get one that is roughly the same strength as the cross-grain strength of the wood that it is holding. Your concerns about hard glue lines are valid and I'm trying to avoid the same.
     
  7. ancient kayaker
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    ancient kayaker aka Terry Haines

    Surely the key issues are, what is the filler doing in addition to merely filling gaps?

    Most obviously it help prevent the gaps from opening, for which job it needs to exceed the cross-grain tensile strength of the wood. If that were all, since the sheathing does a better job in that direction why worry about the filler at all?

    But that's not all.

    The filler also prevents the strips sliding longitudinally, since in this direction sheathing is least effective. For this, the "filler" needs good sheer strength. For most wood the shear strength is about 3 times greater than the cross-grain tensile strength. For cedar with a cross-grain tensile strength of around 300 psi the shear strength would be around 800 psi according to some references.

    I have encountered widely varying values for adhesive shear strength which I do not know how to interpret, since I am not that kind of engineer. When knowledge fails me, suspicion and distrust immediately turn on. The higher demands for resisting longitudinal movement between strips compared to simple gap widening certainly suggest caution, and perhaps testing of samples. I am a firm believer in the value of making and breaking a few test pieces as a backup to theory and faith.
     
  8. rwatson
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    rwatson Senior Member

    Bowdidge has been using this system for some years now

    http://www.bowdidgemarinedesigns.com/Bowdidge_Marine_Designs_1/Strip_Plank.html
     
  9. LP
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    LP Flying Boatman

    Bowdidge's is website was very instrumental in my choice of methods. I'm still planning on a more structural gap filling mix with non-structural sheathing. From what I could glean from his site, he is relying on his sheathings for strength and the strips are his core material. It doesn't specify, but he is going to have heavier sheathing schedules for his boats.
     
  10. rwatson
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    rwatson Senior Member

    I've seen his videos, and spoken to him on the phone. He is a trained NA, and I am sure he would be able to recommend materials, if even for a small 'contribution'
     
  11. LP
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    LP Flying Boatman

    What are you talking about?
     
  12. redreuben
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    redreuben redreuben

    From what I have seen Bowdidge doesn't cut a bevel on his planks but uses a spacer instead, this means the adhesive can squeeze through and make a mess on the inside, also using the double headed nails is way faster and leaves smaller holes to fill than using screws to fix the planks.
     
  13. rwatson
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    rwatson Senior Member

    I am talking about his professional ability and availability for the OP to find out what 'goo' he uses and what glass specs should be used, that you said would be needed for the techqique.

    Redrube - he recommends having a very stiff filler, and a second person underneath to fair off as they go.

    The real benefit of the technique is that you can have the entire hull strip planked without having to spread epoxy or other adhesive between planks.

    The normal process of mixing goo, applying it to each plank, fitting and placing the plank while coping with dripping epoxy, and sometimes having to wait for some planks to set, before you can continue the build, is a great concept.

    To be bale to have all the planks fastened, checking for fairness, and then doing the adhesive in one or two steps is a great concept.
     
  14. redreuben
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    redreuben redreuben

    rwatson;
    Read my first post on this topic :)
     

  15. rwatson
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    rwatson Senior Member

    " ..... this means the adhesive can squeeze through and make a mess on the inside ....."

    Where you don't mention having a person underneath to clean up when using non beveled planks, you mean ?

    The idea of beveling the planks before hand to make less underneath cleaning seems good on paper, but places a lot of pressure on the builder to conform to the plank layup, inside of following the hull lines. Having to bevel stealer planks, or even a gradual taper for end planks, all seems a bother, when it can be catered for on the day with a second hand under the planks.

    I was also 'selling' the concept to other readers, though I can see that you are a convert on the basic principle.

    ps - I thought of it first - in 2008

    http://www.boatdesign.net/forums/wo...oblems-could-building-method-cause-24170.html
     
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