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[bolger] Door skins & glass

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  • David Ryan
    Fellow Bolger Boat Builders -- I ve been wondering about using very thin plywood in combination with a heavier glass job to make very light boat (kayaks,
    Message 1 of 8 , Oct 30, 1999
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      Fellow Bolger Boat Builders --

      I've been wondering about using very thin plywood in combination with
      a heavier glass job to make very light boat (kayaks, hollow paddle
      boards, etc.)

      The function (in my mind, at least, ) of the ply is to provide a
      shape to lay the glass over. The real strength of the whole thing is
      in the framing and glasswork.

      Anyone have any insights into whether or not this is a good idea, and
      why or why not?

      Yours in boat building,

      David Ryan
      Minister of Information and Culture
      Crumbling Empire Productions
      (212) 247-0296
    • Robert N. Lundy
      Actually, this is cored fiberglass construction; just like the guy who built a Skimmer using blue insulation material as the core for lightness and it seems
      Message 2 of 8 , Oct 30, 1999
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        Actually, this is "cored" fiberglass construction; just like the guy who
        built a Skimmer using blue insulation material as the core for lightness
        and it seems to have worked).

        The guys at Fiberglass Coatings indicated if you were building for "stiff"
        (as opposed to "abrasion") you would use lots of mat and woven roven to
        build thickness fast. Mat gives rigidity, glass cloth give abrasion
        resistance and hardness.

        Most core construction happens in a mold because the underlying coring is
        usally quite fragile (balsa, klegecell) and won't hold fastenings prior to
        glassing. Doorskins might be a workable idea.

        Robert Lundy
        St. Petersburg, Fla.

        > -----Original Message-----
        > From: David Ryan [mailto:david@...]
        > Sent: 30 October, 1999 4:17 PM
        > To: bolger@egroups.com
        > Subject: [bolger] Door skins & glass
        >
        >
        > Fellow Bolger Boat Builders --
        >
        > I've been wondering about using very thin plywood in combination with
        > a heavier glass job to make very light boat (kayaks, hollow paddle
        > boards, etc.)
        >
        > The function (in my mind, at least, ) of the ply is to provide a
        > shape to lay the glass over. The real strength of the whole thing is
        > in the framing and glasswork.
        >
        > Anyone have any insights into whether or not this is a good idea, and
        > why or why not?
        >
        > Yours in boat building,
        >
        > David Ryan
        > Minister of Information and Culture
        > Crumbling Empire Productions
        > (212) 247-0296
        >
        > ------------------------------------------------------------------------
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      • Ron Badley
        David, Glass/resin is not a very light weight material for building boats. If you were to use 1/8 ply and cover it with several layers of glass you would
        Message 3 of 8 , Oct 30, 1999
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          David,

          Glass/resin is not a very light weight material for building
          boats. If you were to use 1/8" ply and cover it with several
          layers of glass you would quickly meet or exceed the weight of
          painted 1/4" plywood and spend a bunch more money.

          In pounds per sqft....

          1/8" door skin .35 (estimate)

          1/4" ply/fir .80

          3/8" ply 1.13

          10 oz cloth/resin .12

          If the boat is small, like a kayak, then 1/8" will be plenty
          strong enough with one or two layers of glass on the outside.
          Quite light as well.

          If the boat is bigger than a kayak and light weight is the
          ultimate goal the best way to go is foam core (not blue foam)
          with carbon fibre. Next will be foam with a less high tech and
          more affordable cloth. Strip cedar is also very light and among
          the more cost effective, depending on where you live. Foam core
          and cloth is not much more expensive than the very good quality
          plywoods. Makes for a light boat that has some insulating
          value, wont sweat and has some built in floatation. Still works
          very well as flat panels for chine construction.

          That said, I built two simple 11'6" double paddle canoes in
          the Bolger fasion a couple years ago. They aren't Bolger boxes,
          but they're close. They have 1/4" ply bottoms with door skin
          for the sides and for the half decks. I taped the seams with
          cloth/epoxy and gave them a good coat of paint. They have held
          up very well, always stored outside, upside down, but not under
          cover. One meet an eary demise this spring due to poor aim by
          me while pitching rocks out of the yard, but the other is still
          going strong. I've never weighed them but I'd guess at about 30
          pounds each. Both were built in about about 12 hours and cost
          less than $100. Thats hard to beat with glass/resin.

          Ron

          >From: David Ryan <david@...>

          > Fellow Bolger Boat Builders --
          >
          > I've been wondering about using very thin plywood in combination with
          > a heavier glass job to make very light boat (kayaks, hollow paddle
          > boards, etc.)
          >
          > The function (in my mind, at least, ) of the ply is to provide a
          > shape to lay the glass over. The real strength of the whole thing is
          > in the framing and glasswork.
          >
          > Anyone have any insights into whether or not this is a good idea, and
          > why or why not?
          >
          > Yours in boat building,
          >
          > David Ryan
          > Minister of Information and Culture
          > Crumbling Empire Productions
          > (212) 247-0296
        • Samson family
          ... It depends on how extreme you want to get. The stiffness of a panel depends on the cube of its thickness, so reducing thickness by half reduces stiffness
          Message 4 of 8 , Oct 31, 1999
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            >From: David Ryan <david@...>
            >I've been wondering about using very thin plywood in combination with
            >a heavier glass job to make very light boat (kayaks, hollow paddle
            >boards, etc.)
            >
            >The function (in my mind, at least, ) of the ply is to provide a
            >shape to lay the glass over. The real strength of the whole thing is
            >in the framing and glasswork.
            >
            >Anyone have any insights into whether or not this is a good idea, and
            >why or why not?

            It depends on how extreme you want to get. The stiffness of a panel depends
            on the cube of its thickness, so reducing thickness by half reduces
            stiffness to one eighth of its original value. This might not matter if the
            boat was originally ridiculously overengineered and superstiff, but if it's
            Bolger we're talking about here, he tends to cut these things very fine.

            Of course the glass will help stiffen things up a little, but the secret of
            light weight is to build out of thick, very light material (say foam, or
            balsa) and put on a strong glass skin either side. That's why foam core
            construction is so common among mean, lean racing machines.

            Bill
            >
            >Yours in boat building,
            >
            >David Ryan
            >Minister of Information and Culture
            >Crumbling Empire Productions
            >(212) 247-0296
            >
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          • Donald Hodges
            I have some experience to relate on both subjects: bad news first - I set out to build a fishing pram light enough for one person to handle in a pickup truck
            Message 5 of 8 , Oct 31, 1999
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              I have some experience to relate on both subjects: bad news first - I set
              out to build a fishing pram "light enough for one person to handle in a
              pickup truck and big enough for two people to fish". It is built of 3/4
              inch blueboard (peeled of its polyethylene scrim, a chore in itself) with
              taped seams and 6 oz cloth/epoxy inside and out. A little over 11 feet
              long, it weighs 80 lb, has a built - in fishbox amidships which stiffens the
              structure somewhat. Alas, it is so flimsy and fragile that it fails the
              "handle in a pickup" test. It has to be trailered or handled on a separate
              padded skid. I glued in doorskin floorboards so that I could walk on the
              sole. It rows nicely, but I got impatient and fitted a 6 hp outboard which
              is rapidly disintegrating the boat. I'll probably give her away to somebody
              who can drag her up on a pond or creek shore. I/4 ply would have been a
              much better choice of materials, probably about the same weight, much more
              rugged, quicker to build and much less expensive. I think blueboard
              laminated on or both sides with doorskin may be interesting for light
              "furniture", but I'm over it as a structural core.

              Now the good news - I have made several sets of oars using doorskins
              laminated in 6 oz cloth both sides. I'll try to paste in a post I made to
              rec.boats.building recently on this subject:

              I have made several pairs of oars using split studs as previously described;
              additionally, I set my circular saw at 45 degrees and rip the stock to
              octagonal shape. I make blades in bulk by laminating 6 oz. glass to both
              sides of 1/8 luan doorskin. My blades are 5 inches by 22 inches, with a
              taper from the 17 inch point to the 22 inch point from 5 inches down to the
              dimension of the stock. The tapered part of the blade fits into the slit
              in the stock, the slit (about 10 inches long) is just the ordinary kerf of a
              saw blade. I also
              radius the corners of the blades using a coin to mark the curve tangent to
              the edges. These oars take a few more minutes but are quite satisfactory .
              If you want curved blades, leave a 1-inch tab on the ends of the blades,
              drill a 1/8 hole and precurve the blades with a piece of wire, cord or
              fishline
              before laminating. The blade will retain about half the curve. Saw off the
              tabs before painting the blades.

              I have also made kayak paddle blades from doorskin, cupped by cutting a
              narrow "dart" in them and putting in a wire stitch before laminating. These
              blades are as designed by Glen-L for their Sea Kayak kit. My shaft,
              however, is laminated by placing black pipe insulating foam over a "Spanish
              windlass" and winding it tight, creating a lightweight form. I laminate
              this with fiberglass tape; makes a 100 inch shaft weighing about a pound.

              Finally, Kurt Hughes used to recommend laminating doorskins into coldmolded
              panels using his "Constant Camber" method, but in recent years he has gone
              to structural foam, reportedly because the doorskin quality was so poor that
              he is wary of penetration/rot in immersed structure. I think it would be OK
              in structures dry-sailed or trailered, but would not bet several hundred or
              thousand hours of labor on it in a big project.

              Don Hodges
              dhodges@...
              http://www.ecoastlife.com
              Your Cyber-Vacation - Loafing on the Emerald Coast
              Small Boats, Building, Fishing, Paddling, Rowing, Sailing

              ----- Original Message -----
              From: Ron Badley <badley@...>
              To: <bolger@egroups.com>
              Sent: Sunday, October 31, 1999 12:24 AM
              Subject: [bolger] Re: Door skins & glass


              > David,
              >
              > Glass/resin is not a very light weight material for building
              > boats. If you were to use 1/8" ply and cover it with several
              > layers of glass you would quickly meet or exceed the weight of
              > painted 1/4" plywood and spend a bunch more money.
              >
              > In pounds per sqft....
              >
              > 1/8" door skin .35 (estimate)
              >
              > 1/4" ply/fir .80
              >
              > 3/8" ply 1.13
              >
              > 10 oz cloth/resin .12
              >
              > If the boat is small, like a kayak, then 1/8" will be plenty
              > strong enough with one or two layers of glass on the outside.
              > Quite light as well.
              >
              > If the boat is bigger than a kayak and light weight is the
              > ultimate goal the best way to go is foam core (not blue foam)
              > with carbon fibre. Next will be foam with a less high tech and
              > more affordable cloth. Strip cedar is also very light and among
              > the more cost effective, depending on where you live. Foam core
              > and cloth is not much more expensive than the very good quality
              > plywoods. Makes for a light boat that has some insulating
              > value, wont sweat and has some built in floatation. Still works
              > very well as flat panels for chine construction.
              >
              > That said, I built two simple 11'6" double paddle canoes in
              > the Bolger fasion a couple years ago. They aren't Bolger boxes,
              > but they're close. They have 1/4" ply bottoms with door skin
              > for the sides and for the half decks. I taped the seams with
              > cloth/epoxy and gave them a good coat of paint. They have held
              > up very well, always stored outside, upside down, but not under
              > cover. One meet an eary demise this spring due to poor aim by
              > me while pitching rocks out of the yard, but the other is still
              > going strong. I've never weighed them but I'd guess at about 30
              > pounds each. Both were built in about about 12 hours and cost
              > less than $100. Thats hard to beat with glass/resin.
              >
              > Ron
              >
              > >From: David Ryan <david@...>
              >
              > > Fellow Bolger Boat Builders --
              > >
              > > I've been wondering about using very thin plywood in combination with
              > > a heavier glass job to make very light boat (kayaks, hollow paddle
              > > boards, etc.)
              > >
              > > The function (in my mind, at least, ) of the ply is to provide a
              > > shape to lay the glass over. The real strength of the whole thing is
              > > in the framing and glasswork.
              > >
              > > Anyone have any insights into whether or not this is a good idea, and
              > > why or why not?
              > >
              > > Yours in boat building,
              > >
              > > David Ryan
              > > Minister of Information and Culture
              > > Crumbling Empire Productions
              > > (212) 247-0296
              >
              > ------------------------------------------------------------------------
              > A shopper's dream come true! Find practically anything on earth at eBay!
              > Come and browse the more than 2 million items up for bid at any time.
              > You never know what you might find at eBay!
              > http://clickhere.egroups.com/click/1140
              >
              >
              > eGroups.com home: http://www.egroups.com/group/bolger
              > http://www.egroups.com - Simplifying group communications
              >
              >
              >
              >
            • berniew@nwlink.com
              ... This idea seems to stem from the mistaken notion that glass is stronger and lighter than wood, especially plywood. It is not, particularly in the stiffness
              Message 6 of 8 , Nov 1, 1999
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                David Ryan wrote:

                > I've been wondering about using very thin plywood in combination with
                > a heavier glass job to make very light boat (kayaks, hollow paddle
                > boards, etc.)

                This idea seems to stem from the mistaken notion that glass is stronger
                and lighter than wood, especially plywood. It is not, particularly in
                the stiffness modulus, which is the most important in boat building. In
                fact fiberglass is a relatively limp material. It is also relatively
                heavy for its strength. Plywood is still one the strongest material
                available on a pound of pound basis.

                Fiberglass is used on plywood boat construction not for strength, but
                for waterproofing and abrasion resistance. On a plywood boat it adds
                almost nothing to the overall strength of the boat.

                To make a very light boat, use the thinnest plywood possible for the
                boat being built and omit using any glass except perhaps on the seams.

                The best way to make something stiff yet light is to separate two
                materials that are very strong in both shear, tension and compresion
                with a very light core. Cores are often some type of foam of balsa
                wood. Strength of the core doesn’t matter, what’s important is how
                friable it is (meaning how well the surface is attached. If you rub two
                pieces of foam together and the surface rubs off the material is
                friable and no good for composite construction. The reason is the skins
                will separate form the core under stress making the structure no longer
                a composite and very weak.) What makes a composite strong is that the
                structure transmits all loads to its strongest part, the skin. A
                composites strength is directly related to how far the skins are held
                apart, the farther apart the stronger. Obviously, if you bend a
                composite structure the skin on the outside of the bend is loaded in
                tension, the inside skin in compression. Here again, fiberglass is very
                weak in compression, especially compared to plywood. Plywood is very
                strong in compression. In short, one of the lightest and strongest
                composites you can make is by gluing very thin plywood to the inside
                and outside of a foam sheet. Blue polyfoam is used in some airplane
                construction because it is light, cheep and relatively unfriable.

                Bernie
                Change is a proccess not an event.
              • GHC
                Actually, glass is very, very, very strong. A good fir might be 14,000 psi in tensile strength (at best with no flaws), but E glass is good for 450,000 psi!
                Message 7 of 8 , Nov 1, 1999
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                  Actually, glass is very, very, very strong. A good fir might be 14,000 psi
                  in tensile strength (at best with no flaws), but E glass is good for
                  450,000 psi! It's relatively dense, though, and a thin sheet of plywood
                  doesn't spread it apart very far for your composite sandwich. Wood is
                  light, and relatively strong, so it's easier to get a lot more wood in a
                  structure than glass (with minimal resin).

                  In bending of a panel, the tensile and compressive stresses do lie on the
                  surface, but the shear flows through the middle, trying to separate your
                  sandwich. Your core needs to have good material properties, like balsa or
                  klegecell, not like blue styrofoam.

                  Gregg Carlson





                  At 02:24 PM 11/1/1999 -0800, you wrote:
                  >David Ryan wrote:
                  >
                  >> I've been wondering about using very thin plywood in combination with
                  >> a heavier glass job to make very light boat (kayaks, hollow paddle
                  >> boards, etc.)
                  >
                  >This idea seems to stem from the mistaken notion that glass is stronger
                  >and lighter than wood, especially plywood. It is not, particularly in
                  >the stiffness modulus, which is the most important in boat building. In
                  >fact fiberglass is a relatively limp material. It is also relatively
                  >heavy for its strength. Plywood is still one the strongest material
                  >available on a pound of pound basis.
                  >
                  >Fiberglass is used on plywood boat construction not for strength, but
                  >for waterproofing and abrasion resistance. On a plywood boat it adds
                  >almost nothing to the overall strength of the boat.
                  >
                  >To make a very light boat, use the thinnest plywood possible for the
                  >boat being built and omit using any glass except perhaps on the seams.
                  >
                  >The best way to make something stiff yet light is to separate two
                  >materials that are very strong in both shear, tension and compresion
                  >with a very light core. Cores are often some type of foam of balsa
                  >wood. Strength of the core doesn�t matter, what�s important is how
                  >friable it is (meaning how well the surface is attached. If you rub two
                  >pieces of foam together and the surface rubs off the material is
                  >friable and no good for composite construction. The reason is the skins
                  >will separate form the core under stress making the structure no longer
                  >a composite and very weak.) What makes a composite strong is that the
                  >structure transmits all loads to its strongest part, the skin. A
                  >composites strength is directly related to how far the skins are held
                  >apart, the farther apart the stronger. Obviously, if you bend a
                  >composite structure the skin on the outside of the bend is loaded in
                  >tension, the inside skin in compression. Here again, fiberglass is very
                  >weak in compression, especially compared to plywood. Plywood is very
                  >strong in compression. In short, one of the lightest and strongest
                  >composites you can make is by gluing very thin plywood to the inside
                  >and outside of a foam sheet. Blue polyfoam is used in some airplane
                  >construction because it is light, cheep and relatively unfriable.
                  >
                  >Bernie
                  >Change is a proccess not an event.
                  >
                  >
                  >------------------------------------------------------------------------
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                  >-- http://www.egroups.com/ChatPage?listName=bolger&m=1
                  >
                  >
                  >
                • bianco@asi.it
                  Just as an added info, Jacques Mertens of bateau.com is reengineering his larger boats (Vagabond and Serpentaire) using thin plywood (6 mm) sandwiched between
                  Message 8 of 8 , Nov 2, 1999
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                    Just as an added info, Jacques Mertens of bateau.com is reengineering
                    his larger boats (Vagabond and Serpentaire) using thin plywood (6 mm)
                    sandwiched between two layers of biaxial fiberglass (9 oz) in epoxy
                    resin. The advantages are not only structural: the 6mm plywood is much
                    easier to bend and wrap around bulkheads than thicker stuff. Jacques
                    says that such sandwich is significantly stronger than 9 mm plywood.
                    According to my computations, though, the gain in weight is very
                    limited if any, and the overall cost is very significantly increased.
                    And, folks, just think about crawling into a 6 meter hull and laminated
                    10 square meters of biaxial cloth...
                    Best, Pippo

                    ghc <ghart-@...> wrote:
                    original article:http://www.egroups.com/group/bolger/?start=643
                    > Actually, glass is very, very, very strong. A good fir might be
                    14,000 psi
                    > in tensile strength (at best with no flaws), but E glass is good for
                    > 450,000 psi! It's relatively dense, though, and a thin sheet of
                    plywood
                    > doesn't spread it apart very far for your composite sandwich. Wood is
                    > light, and relatively strong, so it's easier to get a lot more wood
                    in a
                    > structure than glass (with minimal resin).
                    >
                    > In bending of a panel, the tensile and compressive stresses do lie on
                    the
                    > surface, but the shear flows through the middle, trying to separate
                    your
                    > sandwich. Your core needs to have good material properties, like
                    balsa or
                    > klegecell, not like blue styrofoam.
                    >
                    > Gregg Carlson
                    >
                    >
                    >
                    >
                    >
                    > At 02:24 PM 11/1/1999 -0800, you wrote:
                    > >David Ryan wrote:
                    > >
                    > >> I've been wondering about using very thin plywood in combination
                    with
                    > >> a heavier glass job to make very light boat (kayaks, hollow paddle
                    > >> boards, etc.)
                    > >
                    > >This idea seems to stem from the mistaken notion that glass is
                    stronger
                    > >and lighter than wood, especially plywood. It is not, particularly in
                    > >the stiffness modulus, which is the most important in boat building.
                    In
                    > >fact fiberglass is a relatively limp material. It is also relatively
                    > >heavy for its strength. Plywood is still one the strongest material
                    > >available on a pound of pound basis.
                    > >
                    > >Fiberglass is used on plywood boat construction not for strength, but
                    > >for waterproofing and abrasion resistance. On a plywood boat it adds
                    > >almost nothing to the overall strength of the boat.
                    > >
                    > >To make a very light boat, use the thinnest plywood possible for the
                    > >boat being built and omit using any glass except perhaps on the
                    seams.
                    > >
                    > >The best way to make something stiff yet light is to separate two
                    > >materials that are very strong in both shear, tension and compresion
                    > >with a very light core. Cores are often some type of foam of balsa
                    > >wood. Strength of the core doesn’t matter, what’s important is how
                    > >friable it is (meaning how well the surface is attached. If you rub
                    two
                    > >pieces of foam together and the surface rubs off the material is
                    > >friable and no good for composite construction. The reason is the
                    skins
                    > >will separate form the core under stress making the structure no
                    longer
                    > >a composite and very weak.) What makes a composite strong is that the
                    > >structure transmits all loads to its strongest part, the skin. A
                    > >composites strength is directly related to how far the skins are held
                    > >apart, the farther apart the stronger. Obviously, if you bend a
                    > >composite structure the skin on the outside of the bend is loaded in
                    > >tension, the inside skin in compression. Here again, fiberglass is
                    very
                    > >weak in compression, especially compared to plywood. Plywood is very
                    > >strong in compression. In short, one of the lightest and strongest
                    > >composites you can make is by gluing very thin plywood to the inside
                    > >and outside of a foam sheet. Blue polyfoam is used in some airplane
                    > >construction because it is light, cheep and relatively unfriable.
                    > >
                    > >Bernie
                    > >Change is a proccess not an event.
                    > >
                    > >
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