Doube Diagonal Planking

Discussion in 'Powerboats' started by CarbonFootprint, Jan 30, 2015.

  1. CarbonFootprint
    Joined: Nov 2009
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    CarbonFootprint Ill-Advised Boat Modifier

    Double Diagonal Planking

    Hello,

    a while ago, I was helping to restore a double-diagonal mahogany planked power boat from the 1930's. The planking was sealed by a layer of linseed-oil (and white-lead, I think) soaked callico but I was wondring recently, what's used to seal double-diagonal planking today?

    Thanks for any info :)
     
    Last edited: Jan 30, 2015
  2. Pericles
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    Pericles Senior Member

  3. gonzo
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    gonzo Senior Member

    I don't thicken the epoxy. It is viscous enough to fill the gap. We have built many boats like that.
     
  4. PAR
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    PAR Yacht Designer/Builder

    Most double diagonal builds used shellac not linseed oil, as the inter layer bonding agent. It would have been a "heavy" mix (7 - 9 pound usually). This actually works well and many HMC yachts (and other builders), broken down for rebuild many decades after construction, still have an intact bond.

    Today, there are several choices. Some prefer polyurethane for some flexibility, others epoxy, other plastic resin or even resorcinol, while even others use nothing except friction and a tight fasten spacing over Irish felt. Of course, there's also about every possible combination of the above employed too.
     
  5. CarbonFootprint
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    CarbonFootprint Ill-Advised Boat Modifier

    Hello all,

    many thanks for sharing your information - the book by Sam Devlin looks very useful!

    All the best :)
     
  6. CarbonFootprint
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    CarbonFootprint Ill-Advised Boat Modifier

    ...actually, could I pose an unrelated question to PAR, please?

    I've had a quick look through your website at your designs - the Cooper Jr is very attractive, but I was wondering why there are "weep holes" in the frames against the side planking?

    When I was working on this old 1930's hull, it had limber holes too, but only in the bilges - I'd be really interested to know why they've been designed into the Cooper Jr so much higher.

    Thanks :)
     
  7. PAR
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    PAR Yacht Designer/Builder

    General building practice is to place a weep where moisture might collect. In this case, the upright futtocks lie against planking and a stringer passes through, you'd have a corner where moisture couldn't travel to the lowest point and drop into the bilge. The net result would be the potential for rot at each intersection, so a weep is provided above each stringer/frame intersection. If you look closely at this area, you'll also see the tops of the stringers are beveled inboard, again to prevent moisture from collecting and being trapped against the planking.
     
  8. CarbonFootprint
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    CarbonFootprint Ill-Advised Boat Modifier

    That makes sense - having zoomed in now, I can see the bevelled edge of the stringers, too.

    Thanks for explaining that :)
     

  9. Easy Rider
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    Easy Rider Senior Member

    I would be inclined to use Dolfinite. A very soft putty-like sealer but only if fasteners were adequate for bonding. It will always be easy to separate for repairs down the road.
     
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