wood-free strip-plank?

Discussion in 'Materials' started by BenD, Jan 25, 2020.

  1. BenD
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    BenD Junior Member

    Thank you for the explanation folks. In layman's terms then, the foam is not stiff enough during the construction phase.
    Even a very high density foam? Or composite board?

    I have found one example online where another design of mr Bowdidge, an Edgetracker 426 were build substituting plywood with Divinycell in Brazil, which is what got me curious, but it is not a strip plank design.
    EdgeTracker 426 https://bowdidgemarinedesigns.com/edgetracker-426/
     
  2. fallguy
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    fallguy Senior Member

    all about how...

    the designer needs to support the how or the effort is doomed

    high density foams are very expensive vs the best marine plywoods; a sheet of 12# Gurit M retails for about 3-400 USD and is only like 3'x6' or so. Heavier cores defeat the purpose of foam core builds. Foam Core is used typically to reduce weight vs ply.

    foam builds are much more complicated as the foam gets laminated a piece at a time vs glassing an entire ply boat side in one day or two; flipping it over and glassing a monocoque in a day r two on the inside

    each foam panel takes a day to build minimum unless you have a massive shop with tons of tables
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    You could use strips of HDPE I suppose, to get a complicated hull shape, welded together, but the most durable colour, is black !
     
  4. fallguy
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    fallguy Senior Member

    btw, for the OP, heavier cores are used in foam builds, but only as needed in transoms and other loading areas...they would be crazy expensive AND heavy for the whole hull
     
  5. Blueknarr
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    Blueknarr Senior Member

    I worked on several projects where foam coring was applied to a female semi-plug, then glassed over.

    Depending on the size of vessel, raw foam, single skinned and double skinned foam was used.

    Your plug will require more structure than one intended for wood construction. We crawled all over a 40 footer. 1x3 with 3 inch gaps on 18 inch spaced transverses. I inch foam with 6 oz inner preskin.

    Fairing convex is much easier than faring a concave mould.
     
  6. Rumars
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    Rumars Senior Member

    I took the time to look at the riptide design. It calls for 13sqm of 9mm WRC or similar timber for the core. That is 0.117 cubic meters, so with WRC at 350kg/cum the core weighs 41kg.

    Obeche has the same weight as WRC, so the core will also weigh 41kg.
    Your average SA pine at 480kg/cum makes the core weigh 56.16kg.
    SA cypress wich, unlike the previously mentioned is considered a durable species, weighs 470kg/cum wich puts the core at 55kg.

    We are talking here about a weight difference of 15kg. That is not going to make any practical difference, you can use whatever wood you want for the core.
     
  7. BenD
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    BenD Junior Member

    Thank you, that is good info. Unfortunately it is not only the price or availability of whatever wood, that has an influence.
    It is also that the use of wood in boats, has a stigma attached, and long down the line it would ease the resale if you could say, there is no wood in the construction of the boat, which can rot. Most mainstream boat builders in SA follow this route.

    If I were to use wood, I'm sure a good marine ply will also do, or importation of Paulownia can be looked into, but the thread was to ascertain the viability of a synthetic material in the construction.
     
  8. Rumars
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    Rumars Senior Member

    In that case your answer is clear, either foam core or monolithic glass. Both methods are common and most boats can be converted over by a NA, but it makes more sense to choose a design intended for foam or monolithic glass from the beginning.
    The actual building system, plug, mold, etc. depends on the specific scantlings. It also usually involves lots of wood, just not in the finished product.
    I can not comment on the SA used boat market but I would be surprised to hear you can recover materials price even if you sell right after first launch.
     
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  9. fallguy
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    fallguy Senior Member

    Pay close attention to Rumars last remark. Starting with a design meant for foam will save you lotsa headaches.
    Foam and ply are interchangeable, but not always and not without pain and suffering..best to find a foam design where the designer has considered the challenges well vs converting a ply design to foam.

    Foam is very flimsy sans glass. And so a good designer will pay attention to dealing with this problem. For example, they may tell you to glass the whole panel, or they may tell you to glass the interior prior to placing it in the jig.

    Some guys really hate torturing foam panels and are dead set against pre-glassing. Personally, a glass on foam panel bends fairly easily, so it doesn't bother me, as long as the torture isn't extreme.

    I really enjoyed building in a female jig. All jokes aside, what made it nice was being able to walk in for bulkhead placements. When the transom was applied; most of our bulkheads and locker bases were placed. This stiffened the hull greatly for flipping and taping the exterior seams.

    Another thing to realize is you can put fairing reliefs in foam that greatly reduce fairing. The reliefs make tapes stay mostly below the fair surface. This is needed to be in the design and reduces materials and efforts when panel construction is needed.

    Find a foam plan; not simply a composite plan. And avoid the pitfalls of trying to convert ply plans.
     
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  10. BenD
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    BenD Junior Member

    Thank you very much folks, I do now have a better understanding of the challenges of a foam core build.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    I'm not sure he will find a great many dedicated foam sandwich plans.
     
  12. fallguy
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    fallguy Senior Member

    He won't. But him modifying a ply to foam plan is foolish. A designer willing to a different story..

    Jacques Mertens is rumored to be modifying all the bateau.com plans to foam, but that is a massive undertaking and have not seen any of them, yet.
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    As you say, it is a method not without its problems, and especially after it is flipped.
     
  14. Rumars
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    Rumars Senior Member

    Just out of curiosity what would be the foam of choice for a small high speed powerboat bottom?
     
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  15. fallguy
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    fallguy Senior Member

    I will venture a guess.
    6mm too light
    12mm starts to suit; depends on horsepower and others
    up from there on beam and horsepower

    My cat hull bottom is 12mm, but pretty narrow; like 22" wide.
     
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