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Re: [bolger] Re: Commonsense Skiff

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  • 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 1 of 20 , Jul 2, 2005
      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 2 of 20 , Jul 3, 2005
        >
        > 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 3 of 20 , Jul 3, 2005
          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
          > - Unsubscribe: bolger-unsubscribe@yahoogroups.com
          > - Open discussion: bolger_coffee_lounge-subscribe@yahoogroups.com
          > Yahoo! Groups Links
          >
          >
          >
          >
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          >
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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 4 of 20 , Jul 3, 2005
            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 5 of 20 , Jul 3, 2005
              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 6 of 20 , Jul 3, 2005
                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 7 of 20 , Jul 3, 2005
                  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 8 of 20 , Jul 3, 2005
                    > 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 9 of 20 , Jul 4, 2005
                      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
                      > - Open discussion: bolger_coffee_lounge-subscribe@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 10 of 20 , Jul 4, 2005
                        --- 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 11 of 20 , Jul 4, 2005
                          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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