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Re: Commonsense Skiff

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  • Howard Stephenson
    Gary, If you go to: http://boatdesign.net/forums/archive/index.php/t-6334 .. you will find useful guidance on foam/glass scantlings. Following the advice
    Message 1 of 20 , Jul 2 9:57 PM
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      Gary,

      If you go to:

      http://boatdesign.net/forums/archive/index.php/t-6334

      .. you will find useful guidance on foam/glass scantlings. Following
      the advice there, you should be able to decide what your scantlings
      would need to be and then compare the calculated weight per unit area
      with that of a ply skin -- and compare the cost too!

      Howard

      --- In bolger@yahoogroups.com, "gbship" <gbship@c...> wrote:> Chris:
      How do you figure scantlings for foam/glass construction? I've
      > done some online looking, but haven't found any resources.
    • Chris Lasdauskas
      ... Gary, as I said it was a few years back, so this may not be right, but I think I used The Elements of Boat Strength for Builders, Designers, and Owners
      Message 2 of 20 , Jul 2 11:41 PM
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        gbship wrote:
        >
        > Chris: How do you figure scantlings for foam/glass construction? I've
        > done some online looking, but haven't found any resources.

        Gary, as I said it was a few years back, so this may not be right, but I
        think I used "The Elements of Boat Strength for Builders, Designers, and
        Owners" by Dave Gerr (though that is copyright 2000, and I thought I did
        this in about 1999..., perhaps I used his "The Nature of Boats"), I
        think I also didn't find much online.

        > A friend
        > laminated a couple layers of glass on either side of 3/8 inch foam (I
        > think that was the thickness) and you could whack it with a hammer
        > without damage and it was considerably lighter than a ply sandwich
        > would have been.

        Which reminds me of this cautionary story from "The Nature of Boats":

        'A Warning About Being Thin-Skinned

        'A final word of warning is in order. When using these high-strength
        fibers and sandwich construction, the skin thickness required for
        overall —- remember overall -— structural strength can become almost
        unbelievably thin, even on quite large vessels. This works out well on
        paper, but what about hitting a floating log? A well-known designer
        related a story both amusing and worrisome. A local builder of large
        (90-foot, 27-meter) high-speed sportfishermen proudly showed him an
        all-Kevlar, foam-sandwich hull panel that he'd used in a couple of
        recent craft. The builder explained that his computer confirmed the
        very, very thin skins (on the inside and outside of the foam) were more
        than up to the job.

        'To demonstrate his point, the builder took a hammer and wacked at the
        sample panel mightily. With the hammer bouncing off harmlessly, he
        offered it confidently to the skeptical architect. Taking the hammer,
        the architect turned it claw-side down and -— with virtually no force at
        all -— drove it right through Kevlar, the foam, and out the other side.
        The builder's face turned white. He had a couple of boats out on the
        water with this layup. The moral -— there's always a moral -— is that
        the structural design of high-tech hulls is a complicated business.
        Before you dash off to build or have built one of these miracle hulls,
        make sure a good naval architect does a detailed structural analysis.'

        That's what I was talking about when I mentioned penetration strength.
        Sure a Gypsy isn't going to hit logs at 30 knots, but the scantlings
        will already be redeuced in proportion to the speed. You can't let the
        skins get too thin. 'Too thin' on foam is thinnner than 'too thin' on
        ply. Avoiding that was where the extra weight came from.

        Chris
      • gbship
        ... strength. ... the ... Thanks everyone for the thought and advice. I should have explained better the use for this boat. It s for an expedition type
        Message 3 of 20 , Jul 3 4:57 AM
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          >
          > That's what I was talking about when I mentioned penetration
          strength.
          > Sure a Gypsy isn't going to hit logs at 30 knots, but the scantlings
          > will already be redeuced in proportion to the speed. You can't let
          the
          > skins get too thin. 'Too thin' on foam is thinnner than 'too thin' on
          > ply. Avoiding that was where the extra weight came from.
          >
          > Chris

          Thanks everyone for the thought and advice. I should have explained
          better the use for this boat. It's for an expedition type competition
          of around 1,000 miles, give or take, for kayaks and small sailboats.
          Among the salient features, are you must beach launch your craft (You
          can use mechanical assistance, but you must carry whatever you use for
          the entire race), the ability to go under a 9-foot high bridge with 10-
          foot horizontal clearance, deal with open water and inland waterways
          churned by powerboat wakes, etc. This race is around the peninsula part
          of Florida, so at one point, competitors have to go up the St. Mary's
          river (in S. Georgia) and then portage their boats 40 MILES to the
          Suwanee. The kayakers balance their boats on a set of wheels, attach
          the bow to the back of their belt and walk it. They can also tow it
          with a folding bike -- as long as they carry the bike for the entire
          race. Obviously this won't work for sailboats, which even in a small
          size weigh much more. So those comeptitors are allowed to switch to a
          canoe for the necessary river portions and the portage. You can see the
          details at Watertribe.com, check the Ultra Florida Challenge section.
          We're only planning to do the shorter Everglades Challenge in 2006, in
          our Frolic2, but I'm intrigued with trying the longer race in 2007. My
          particular itch right now is to wonder if a small sailboat could be
          built light enough so that switching to the canoe would be unnecessary,
          even for the portage (which I would do with a bike!).

          But, alas, I know almost nothing of composite construction, which is
          why everyone's advice is so helpful and much appreciated. It does no
          good to have an ultralight hull if it's punctured by a razor sharp
          shell on an oyster bar, or a cypress knee or mangrove root in the
          Everglades, or by a rock or log in the Suwanee. The weight concern is
          why I've been mostly looking at ply instant-type boats in the 125 to
          150 pound range and wondering if that weight could be cut in half with
          composite construction. There are intriguing hints. For example, my 25-
          30 pound solid wood mast on the Rolic2 could be replaced by a carbon
          fiber spar that would weight less than 10 pounds. In Pete Goss' book
          about single handed racing around the world, he mentions that the bare
          hull of his 50 footer could be turned over by 6 husky guys --- about
          what the 1/2 inch ply/fiberglass bare hull weighs on our 30-footer
          (which is a Gypsy-type hull).

          BTW Graeme, thanks for the suggestion of the Zephyr, but I ruled that
          out because while it is an excellent daysailer and can handle some
          nasty weather, it doesn't row very well, possibly because the 16-inch
          sides are too high. (I had one for many years, and was very fond of it.)

          Gary Blankenship
        • John B. Trussell
          There have been various threads wich suggest that PCB doesn t design racing boats. You might take a look at Paul Gartside s web site--His Flashboat is a
          Message 4 of 20 , Jul 3 6:09 AM
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            There have been various threads wich suggest that PCB doesn't design
            "racing" boats. You might take a look at Paul Gartside's web site--His
            Flashboat is a very light, very fast row boat and he has camp cruised around
            Alaska in it.

            It appears to me that the rules you described favor a kayak with a sail.
            I've always thought that a two person rowing boat would do well in this sort
            of race--the two rowers could alternate and maintain speed more or less
            continuously; they would also have the ability to row together and buck
            currents if needed.

            I'm way too old and decrepit to participate or even enjoy the kind of boat
            needed for this kind of event, but iy si fun to think about.

            John T
            ----- Original Message -----
            From: "gbship" <gbship@...>
            To: <bolger@yahoogroups.com>
            Sent: Sunday, July 03, 2005 7:57 AM
            Subject: [bolger] Re: Commonsense Skiff


            > >
            > > That's what I was talking about when I mentioned penetration
            > strength.
            > > Sure a Gypsy isn't going to hit logs at 30 knots, but the scantlings
            > > will already be redeuced in proportion to the speed. You can't let
            > the
            > > skins get too thin. 'Too thin' on foam is thinnner than 'too thin' on
            > > ply. Avoiding that was where the extra weight came from.
            > >
            > > Chris
            >
            > Thanks everyone for the thought and advice. I should have explained
            > better the use for this boat. It's for an expedition type competition
            > of around 1,000 miles, give or take, for kayaks and small sailboats.
            > Among the salient features, are you must beach launch your craft (You
            > can use mechanical assistance, but you must carry whatever you use for
            > the entire race), the ability to go under a 9-foot high bridge with 10-
            > foot horizontal clearance, deal with open water and inland waterways
            > churned by powerboat wakes, etc. This race is around the peninsula part
            > of Florida, so at one point, competitors have to go up the St. Mary's
            > river (in S. Georgia) and then portage their boats 40 MILES to the
            > Suwanee. The kayakers balance their boats on a set of wheels, attach
            > the bow to the back of their belt and walk it. They can also tow it
            > with a folding bike -- as long as they carry the bike for the entire
            > race. Obviously this won't work for sailboats, which even in a small
            > size weigh much more. So those comeptitors are allowed to switch to a
            > canoe for the necessary river portions and the portage. You can see the
            > details at Watertribe.com, check the Ultra Florida Challenge section.
            > We're only planning to do the shorter Everglades Challenge in 2006, in
            > our Frolic2, but I'm intrigued with trying the longer race in 2007. My
            > particular itch right now is to wonder if a small sailboat could be
            > built light enough so that switching to the canoe would be unnecessary,
            > even for the portage (which I would do with a bike!).
            >
            > But, alas, I know almost nothing of composite construction, which is
            > why everyone's advice is so helpful and much appreciated. It does no
            > good to have an ultralight hull if it's punctured by a razor sharp
            > shell on an oyster bar, or a cypress knee or mangrove root in the
            > Everglades, or by a rock or log in the Suwanee. The weight concern is
            > why I've been mostly looking at ply instant-type boats in the 125 to
            > 150 pound range and wondering if that weight could be cut in half with
            > composite construction. There are intriguing hints. For example, my 25-
            > 30 pound solid wood mast on the Rolic2 could be replaced by a carbon
            > fiber spar that would weight less than 10 pounds. In Pete Goss' book
            > about single handed racing around the world, he mentions that the bare
            > hull of his 50 footer could be turned over by 6 husky guys --- about
            > what the 1/2 inch ply/fiberglass bare hull weighs on our 30-footer
            > (which is a Gypsy-type hull).
            >
            > BTW Graeme, thanks for the suggestion of the Zephyr, but I ruled that
            > out because while it is an excellent daysailer and can handle some
            > nasty weather, it doesn't row very well, possibly because the 16-inch
            > sides are too high. (I had one for many years, and was very fond of it.)
            >
            > Gary Blankenship
            >
            >
            >
            >
            > Bolger rules!!!
            > - no cursing, flaming, trolling, spamming, or flogging dead horses
            > - stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
            > - Pls add your comments at the TOP, SIGN your posts, and snip away
            > - Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930, Fax:
            (978) 282-1349
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          • Gary Lepak
            Gary, For what it s worth, I once built a Bolger Dolphin, (Small Boats, Design #259, 18 x 4 ) out of 3/8 Airex foam with two layers of 6 oz glass inside and
            Message 5 of 20 , Jul 3 6:25 AM
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              Gary,

              For what it's worth, I once built a Bolger Dolphin, (Small Boats, Design
              #259, 18' x 4') out of 3/8" Airex foam with two layers of 6 oz glass inside
              and out. It was a stripped down rowboat version, no centerboard, rudder or
              rig. It weighed about a 100 lbs. I never weighed it, but two people could
              throw it over their heads like a canoe. It seemed quite tough, and I never
              worried about punctures or breakage. Of course it is a compound curved
              hull so the bulding took some time with lofting and moldmaking, but you
              would get a strong light hull this way. These days I would use Corefoam,
              though it is expensive.

              For a cheaper light boat that would be quicker to build I might try
              lapstrake plywood. You could vary the plank thickness, say 4 to 5 mm on the
              bottom and 3mm topsides.

              Gary Lepak
              Port Angeles, WA
            • Howard Stephenson
              To see a boat that is suitable for South Georgia, go to: http://www.ibiblio.org/ebooks/Shackleton/South/057.jpg Howard ;-]
              Message 6 of 20 , Jul 3 1:32 PM
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                To see a boat that is suitable for South Georgia, go to:

                http://www.ibiblio.org/ebooks/Shackleton/South/057.jpg

                Howard ;-]

                --- In bolger@yahoogroups.com, "gbship" <gbship@c...> wrote:

                > so at one point, competitors have to go up the St. Mary's
                > river (in S. Georgia) and then portage their boats 40 MILES
              • graeme19121984
                Perhaps *the* small boat team time trial endurance event.
                Message 7 of 20 , Jul 3 3:50 PM
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                  Perhaps *the* small boat team time trial endurance event.

                  --- In bolger@yahoogroups.com, "Howard Stephenson" <stephensonhw@a...>
                  wrote:
                  > To see a boat that is suitable for South Georgia, go to:
                  >
                  > http://www.ibiblio.org/ebooks/Shackleton/South/057.jpg
                  >
                  > Howard ;-]
                  >
                  > --- In bolger@yahoogroups.com, "gbship" <gbship@c...> wrote:
                  >
                  > > so at one point, competitors have to go up the St. Mary's
                  > > river (in S. Georgia) and then portage their boats 40 MILES
                • James Greene
                  Wow, when I was thinking abut glass over foam construction I was considering 1 inch foam or thicker for the hulls. You guys are using foam that s less than
                  Message 8 of 20 , Jul 3 11:42 PM
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                    Wow, when I was thinking abut glass over foam construction I was
                    considering 1 inch foam or thicker for the hulls. You guys are using
                    foam that's less than half this thickness! Interesting ...

                    James Greene


                    On Jul 3, 2005, at 09:58, gbship wrote:

                    > A friend
                    > laminated a couple layers of glass on either side of 3/8 inch foam (I
                    > think that was the thickness) and you could whack it with a hammer
                    > without damage and it was considerably lighter than a ply sandwich
                    > would have been. I made some hatches for our Frolic2 of glass over 1/4-
                    > inch foam and those are reasonably strong, and very light, but not
                    > strong enough for use for a hull.
                  • James Greene
                    ... I wonder if the cheapest available foam might not be good enough for most small boats, provided it fills the void between the inner and outer skins and
                    Message 9 of 20 , Jul 3 11:49 PM
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                      > These days I would use Corefoam,
                      > though it is expensive.

                      I wonder if the cheapest available foam might not be "good enough" for
                      most small boats, provided it fills the void between the inner and
                      outer skins and does not separate from them. Does this leave out good
                      old fashioned styrofoam I wonder?

                      James Greene
                    • Clyde Wisner
                      I think I used inch and a half foam for my Brick and had to use a lot of glass and epoxy to get strength to stand in. I also made a deck of sorts from 1/4 ply
                      Message 10 of 20 , Jul 4 6:51 AM
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                        I think I used inch and a half foam for my Brick and had to use a lot of
                        glass and epoxy to get strength to stand in. I also made a deck of sorts
                        from 1/4 ply so the sides wouldn't bolge out. Overall, not worth the
                        money in glass and epoxy, and the trouble. If you do go forward, I would
                        think a multi
                        chine rather than large flat areas like the bottom of a Brick. My foam
                        Brick floats upside down of course and almost floated away during
                        Isabell, which might not have been bad. Clyde.


                        James Greene wrote:

                        > > These days I would use Corefoam,
                        > > though it is expensive.
                        >
                        > I wonder if the cheapest available foam might not be "good enough" for
                        > most small boats, provided it fills the void between the inner and
                        > outer skins and does not separate from them. Does this leave out good
                        > old fashioned styrofoam I wonder?
                        >
                        > James Greene
                        >
                        >
                        >
                        >
                        >
                        >
                        > Bolger rules!!!
                        > - no cursing, flaming, trolling, spamming, or flogging dead horses
                        > - stay on topic, stay on thread, punctuate, no 'Ed, thanks, Fred' posts
                        > - Pls add your comments at the TOP, SIGN your posts, and snip away
                        > - Plans: Mr. Philip C. Bolger, P.O. Box 1209, Gloucester, MA, 01930,
                        > Fax: (978) 282-1349
                        > - Unsubscribe: bolger-unsubscribe@yahoogroups.com
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                        [Non-text portions of this message have been removed]
                      • Chris Stewart
                        ... the ... at ... side. Consider skin on frame constuction using 26 ounce double ply woven nylon skin. Quoting from UMIAK An Illustrated Guide by Skip
                        Message 11 of 20 , Jul 4 7:03 AM
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                          --- In bolger@yahoogroups.com, Chris Lasdauskas <cml@t...> wrote:
                          > 'To demonstrate his point, the builder took a hammer and wacked at
                          the
                          > sample panel mightily. With the hammer bouncing off harmlessly, he
                          > offered it confidently to the skeptical architect. Taking the hammer,
                          > the architect turned it claw-side down and -— with virtually no force
                          at
                          > all -— drove it right through Kevlar, the foam, and out the other
                          side.


                          Consider skin on frame constuction using 26 ounce double ply woven
                          nylon skin. Quoting from "UMIAK An Illustrated Guide" by Skip Snaith:
                          "The 26-ounce double-weave nylon skin on Tim's boat was incredibly
                          tough; you could hit it with the claw end of a hammer as hard as you
                          liked, and the hammer would bounce back."

                          Skin on frame can produce very light boats. Platt Monfort's Geodesic
                          Aerolight boats are incredibly light, but probably not strong enough
                          for the Watertribe Challenge. Up the scantlings a bit, with the frame
                          lashed rather than glued to preserve flexibility, and use a much
                          tougher skin and you'd end up with a light, resilient boat.

                          Chris Stewart
                        • Gary Lepak
                          James, The boatbuilding foams like Airex, Corecell and Divinicell are more dense than styrofoam. 5 to 8 lbs per cubic ft. compared to 1.1 (white) to 2 (pink
                          Message 12 of 20 , Jul 4 7:16 PM
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                            James,
                            The boatbuilding foams like Airex, Corecell and Divinicell are more dense
                            than styrofoam. 5 to 8 lbs per cubic ft. compared to 1.1 (white) to 2
                            (pink or blue). The lighter the foam the thicker the skin needs to be to
                            maintain the bond when struck. I've built two boats from blue foam, a tri
                            that didn't last very long made of 1" thick foam with glass/epoxy skins,
                            and a solid foam paddleboard I still have. The board has two layers of 6
                            oz glass in epoxy resin on the bottom and a 3mm ply deck. The two layers of
                            6 are about minimum I think, and it is still easily punctured or dented. It
                            just doesn't matter much if it is, as it still floats, being solid foam. If
                            you are always building boats with epoxy anyway, you fill the dings easily.
                            The ply deck seems to take a lot of abuse without delaminating though, and
                            could make a good boat with 1" foam inside 3mm ply with glass inside, but
                            would probably weigh as much as 1/4" ply. I like using the blue foam though
                            and still use it for things like outrigger floats or sponsons, i.e. solid
                            foam objects with glass skin, rather than as a foam sandwich hull skin .
                            Gary Lepak


                            ----- Original Message ----- > I wonder if the cheapest available foam might
                            not be "good enough" for
                            > most small boats, provided it fills the void between the inner and
                            > outer skins and does not separate from them. Does this leave out good
                            > old fashioned styrofoam I wonder?
                            >
                            > James Greene
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