A Hull Sheathing Alternative?

Discussion in 'Wooden Boat Building and Restoration' started by Wayne Grabow, Nov 14, 2010.

  1. Wayne Grabow
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    Wayne Grabow Senior Member

    Just finished building a boat and, of course, am starting to think about a next one. I have an idea about sheathing/planking that I'd like some advice and opinions on. On the last boat I sheathed the entire developable hull in 6mm marine ply then added a bonded layer of cypress 3/16" thick planking with fiberglass & epoxy over that. Marine plywood is expensive. What if instead I used three bonded layers of wood planking? I am thinking about an initial layer of 5 mm. thick by 3" wide planking laid longitudinally followed by a 4-5 mm. by 3" layer laid approximately to follow the ruling lines (laterally) and then another layer running fore and aft with edge joints offset from the first layer. This would then be covered by fiberglass and epoxy.

    Multiple layers like cold molding, but not veneers. Strips set edge to edge like strip planking, but using 3" wide pieces. Less expensive than veneer and faster to lay down than narrow strips. 4-5 mm. thicknesses will adapt to a curve readily without heavy clamping. The middle layer and the outer fiberglass should provide across grain stabilization. The finished product will have the look of solid wood.

    What do you think? Is it a bad idea, or does everyone else already use a similar technique that only I didn't know about?
     
    Last edited: Nov 14, 2010
  2. Landlubber
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    Landlubber Senior Member

    ...you have just described tripple diagonal planking (cold moulded), used by boatbuilders with epoxy for over 40 years that I have experience with....some famous aussie boats were built like that by Cec Quilkey at Taren Point, boats such as Ragamuffin...used more than 3 layers, but the same story.

    It is a very strong way to make a boat.
     
  3. michael pierzga
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    michael pierzga Senior Member

    Many of the triple planked boats I see suffer from the inside of the hull out. its impossible to Waterproof, epoxy ,stabilize the inside of the planking. Just to many areas that might go wrong. If its a simple boat without a lot of interior structure its probably ok. Plywwod is more stable than wood planking and hence seems to be the logical route for most construction.
    Triple planking is a great way to build a boat...Im looking at a 40 year old triple planked round bilge, Italian built motoryacht right now in the shipyard and she looks very tight, very fair. She is traditional triple planking. Her only damage...and the reason she is out of the water is because a dripping shower stall fitting damaged the inside planking under the head area. .

    The designer builder Paul Gartside has so thoughts on it...you might check it out on the internet.
     
  4. apex1

    apex1 Guest

    What a utter nonsense.

    As Landlubber said, it is a proven way of producing strong hulls. And there is nothing difficult in making the entire hull waterproof.

    Plywood has the disadvantage of wrong orientation of fibres in at least 40% of the plies. Your statement that it is "more stable" is completely wrong.
     
  5. gonzo
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    gonzo Senior Member

    I agree with Apex. Triple planking has been used for about a century. With epoxy it is much easier to build.
     
  6. NoEyeDeer
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    NoEyeDeer Senior Member

    It's an awesome way to build a boat, but it's a lot of work and it has never been regarded as a particularly cheap method. You'll be using a lot of glue and staples and I think 5mm would have to be sawn, so there's considerable wastage of timber. I wouldn't consider using it for any boat that had developable surfaces anyway (like your old boat). Boats like that are better suited to ply IMO. If your new boat is not going to be developable then triple planking is worth looking at, but these days strip planking with glass sheathing is used more often.
     
  7. PAR
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    PAR Yacht Designer/Builder

    Actually, the most common "way" would to diagonally mold over strip planking.
     
  8. Wayne Grabow
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    Wayne Grabow Senior Member

    Thank you. Now I know the name, triple diagonal planking. Because the hull is a developable shape, the planking can be run in several convenient directions; so the "diagonal" description makes sense for the two inner planking layers. Working alone, one of my least favorite tasks was to handle the large sheets of plywood; positioning, bonding, clamping in a timely fashion while working clean. Individual planks should be much more convenient.

    For my recent boat the plywood came all the way from Toronto. Colorado is not boating country, but solid wood can be obtained in this area. At a 2300 meter altitude here, the humidity is quite low year around which is nice for dimensional stability. Below the chine, I will use fiberglass cloth on the inside also which help seal it.

    Today it snowed here twice; boating season is over. Tomorrow I take the boat I just completed to the upholsterer for a travel cover, bimini top and cushions. Then it gets put away until spring.
     
  9. Landlubber
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    Landlubber Senior Member

    Wayne, you sheath the whole boat when it is finished with cloth, both sides......what is known as a "balanced" laminate (same inside as outside)....epoxy, not poly.
     
  10. PAR
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    PAR Yacht Designer/Builder

    This type of building actually called molded, not triple diagonal. Diagonal planking suggests a different technique, using planks, not thick veneers.

    As has been mentioned, molding a developed surface isn't best utilization of materials or labor. If you have a developed surface, sheet goods, such as plywood or sheet metal are much more advantageous, both in materials and labor, not to mention waste.

    Also 'glassing just below the LWL isn't usually the best idea, as it sets up the perfect environment for moisture ingress along the transition area, where the 'glass sheathing stops and the planking remains.

    It's often difficult to match the abilities and physical properties of plywood. This is one reason it has taken over many industries by storm in the last 60 years. The idea of thick veneers has been used, but it usually sets up internal stresses, in the veneers themselves, causing checking, cupping, curling and other assorted issues. This is why plywood works, the veneers used in panel construction are thin enough to eliminate these issues and of course assembled under huge pressures..

    Lastly, it's just silly to not use sheet goods on a developed surface. Given a choice between a plywood skin and several layers of veneers, the labor costs alone offset any material savings. Also a molded hull requires a substantial "buck" to apply the first few layers of veneer on. A plywood skin can be applied over fairly widely spaced station molds, which saves even more in materials and labor.

    This said the thick veneer idea can be very effective in round bilge shapes and honestly would be the only place I would consider taking on the extra labor (having to plank the complete hull for each veneer layer for example). If you kept the veneers below 4 mm, you'd be just molding, but once you go over this thickness, you'll start seeing the issues common of thick veneer planking. Also the thick veneers can't conform to all compound curves, so some shape limitations will exist with this method, while you have none with 4 mm and thinner planking.
     
  11. michael pierzga
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    michael pierzga Senior Member

    for the interior skin off a mutiskin hull , the first lamination, plywood has better duribility. I see it on old boats. When the epoxy is banged or dinged, plywood doesnt wick water as fast as timber. The interior of yachts takes a beating during their life. .
    As Par states , developing the first skin with plywood is also much easier.
     
  12. Landlubber
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    Landlubber Senior Member

    "...you have just described tripple diagonal planking (cold moulded), "

    ......here we call both types triple diagonal, the old version was done with three layers of solid wood, canvassed often between, and mechanically fastened, either with roves or simply bent nails (double tucked), the "new" version is of course epoxy glued and stapled (cold moulded)
     
  13. michael pierzga
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    michael pierzga Senior Member

    Ya the triple skin Italian motorboat in the shipyard is canvas between layers. Canvas and " white stuff" I guess white lead ? The yacht looks in very good condition for its age.
     
  14. Landlubber
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    Landlubber Senior Member

    ...yep,, it was white lead.
     

  15. apex1

    apex1 Guest

    That is wrong again.

    As a first "strip" on cold moulded hulls ply is the weaker material than solid timber.
    Your repeatedly stated difficulty to encapsulate the timber completely, is wrong also. That is done daily in wood epoxy building, and provides a wear resistant surface on both sides when done right.
    You should learn what "developing" a skin means....btw.

    I agree with Paul that in this case, where the skin is developable, ply sheets are much easier to apply and save a lot of money and labour.
    When the veneer goes over 4mm we call it a plank, instead of veneer. Hence both was right. With these thick layers one usually has to go narrower in strip width, to follow curvature. The method is the same as cold moulding, but with such a relatively thick "plank" I would call it triple planked instead.

    But again, in this case, sheathed ply is the way to prefer.

    Regards
    Richard
     
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