2005 43’ Trawler w/ Marine Plywood Core in Deck and Pilot House – Major Concern?

Discussion in 'Boat Design' started by TJB_Patriot, Feb 16, 2011.

  1. viking north
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    viking north VINLAND

    As well as a boatbuilder i am also journeyman licenced carpenter. I have been asked many times by prospective customers, can you build me the perfect house and my answer is always the same, can't do it, I am not the perfect man and God didn't grow perfect trees. Likewise for boats, there's no perfect material and even if there were people would find fault and have a different opinion. Material selection is a result of target market, customer choice financial or otherwise and somewhere down the line wear,tear and aging requires repairs and creates employment for some man to feed his family. In our Capitalistic system it is the duty of those without the financial means to buy food or toys to take that money thru honest work from those that have. Would you have it anyother way. Foam has it's weakness also, it must be reinforced with ply where thu bolting is required thus at those points it is effectively a ply core and at the most vunerable location for water penetration(fasteners). Overall a foam cored area is less vunerable but in the sceme of things a properly laid and maintained ply core deck ( key word deck) is stronger, more versatile and should not be a negative when purchasing or building a vessel. ---Geo.

    A yacht is not defined by by the vessel but by the care and love of her owner
     
  2. u4ea32
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    u4ea32 Senior Member

    I agree with Viking, well put.

    Personally, my experience is that plywood, or other uses of wood for structure, result in pain and suffering for the owner.

    There are lots of boats with plywood decks that are decades old. Some are famous for durability (Cal 40, Grand Banks), some are famous for problems (many Taiwanese built boats). Some uses are common (powerboat transoms and under deck hardware), yet are commonly known as problems after only a few years. Specifically, on very many boats, life line stanchions are wobbly, and winch bases leak, due to the failure of the plywood cores.
     
  3. Steve W
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    Steve W Senior Member

    Any boat where a plywood deck required any maintainance at all in the first 3 years of life was not built by a builder deserving of any respect,that was one schlock builder. Unfortunatly i too have seen such poor workmanship, the material was not at fault,the builder was.
    Steve.
     
  4. gonzo
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    gonzo Senior Member

    u4ea42: I disagree very much. Plywood structures last many years. What do you base your opinion on? Even the cheaply built plywood transoms, left with the end grain exposed, last 12-15 years.
     
  5. FAST FRED
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    FAST FRED Senior Member

    "Foam has it's weakness also, it must be reinforced with ply where thu bolting is required thus at those points it is effectively a ply core."

    This is only the cheapest construction , used decades ago,not what is usually done these days.
     
  6. viking north
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    viking north VINLAND

    Fred as far as i am aware, it is still commonly used today and if properly done there is nothing wrong with it. I am curious though other than ply or solid FRP what is being used to take compression loads. I used ply core in repairs and mods right up to shutting down the shop and never had any problems. In my new personal build I will use it in areas requiring extra strength and loading. I really don't see why all the concern with proper care in fabrication and after maintenance it's literally bulletproof. If not it will require a repair which should show up on a top notch survey which will make or break a deal in pricing. Speaking of surveys has the field advanced to the use of a type of ultra sound or infra red technology? The infra red would certainly be useful much the same way as we use in house construction. Heat up the underdecks area and look for hot spots in the cored deck (ply or balsa) from above with the camera, as would be indicated by greater heat conduction thru joins, voids, rotted or wet cores. If not someone aught to consider this tool. House, boats, autos, legal, whatever if one is not highly familiar with the product as preached by others long before my time, hire the best to protect your proposed investment, 99.9% of the time they save their own fees plus a big hunk of your lifes sweat and toil. Geo

    A yacht is not defined by the vessel but by the love and care of her cored deck :)
     
  7. gonzo
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    gonzo Senior Member

    I use infrared in conjunction with a moisture meter. It even shows screws and keel bolts.
     
  8. viking north
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    viking north VINLAND

    Gonzo, what a great tool especially for large deck areas, i know it will respond to a wet spot in the core by greater conductivity of the heat thru the deck, does it give a good reading I.E. thru say a dry rotted area,(powered wood) as it could be possible the dry powered rotted wood would be as good an insulator as say solid ply. Then again the dry rot power would certainly be picked up by a change in tone of a rubber hammer but the infrared would be faster. You say keel bolts, does it require a heat gun on one side of the floor timbers and along the keel root to get the readings from the opposite side ? How detailed are the readings, good enought to determine accurately the amount of corrosion or just to say yes there is some corrosion. Interesting info. that i've always wondered about wheather it was in use or not. --Geo.
     

  9. u4ea32
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    u4ea32 Senior Member

    Apparently you and I have very different experiences. I guess that's OK.

    I see some plywood structures that last.

    I see some that have major problems, especially in situations where plywood is "supposed" to be used, such as under deck fittings and in transoms, and I have seen these problems in many boats that are only a handful of years old. My boat's transom was built with high grade marine plywood in vinyl ester laminated and heavy multi-axial stitched glass. And yet in 10 years, it was rotten, and I had to have it replaced. The builder has subsequently gone to high density foam the transoms.

    So again, in my experience (that may be different from other's experience) I see problems with using wood for structural purposes on boats.

    Water causes problems with nearly all materials (including plastic -- witness blisters). Controlling water ingress into structures is critical, hence materials that are highly resistant to water molecule migration (linear polyurethane paints, epoxy and vinyl ester resins) must be used. If, say, epoxy is used and raw wood is never exposed, then it can be OK. The problem is that cracks do occur, manufacturing defects do occur, holes will be drilled and caulking does break down. Therefore, one should consider strongly what happens to the structural material when it does get wet, because it almost certainly will eventually get wet.
     
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