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Elon Jessup plywood

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  • rljssn
    I ve been trying to work out which skiff and what material for too long. I like these old skiffs but the traditional woods in decent grain are turning out just
    Message 1 of 5 , Dec 16, 2005
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      I've been trying to work out which skiff and what material for too
      long. I like these old skiffs but the traditional woods in decent grain
      are turning out just as expensive as the marine plywood in my area. In
      the description story on Jessup it mentions 1/2" rotary cut Bruynzeel
      plywood as a substitute. Is there any more information or a precedent
      from boats built as to how to make this substitution? Is there anything
      in the scantilings table about the planking? 1/2" ply in the sides and
      a double thickness on bottom maybe?

      I think I can live with the non-traditional materials but I don't want
      to lighten this design and change the load waterline characteristics.

      thanks for all the great advice,
      at least I've got a favorite skiff picked out.-Russell

      ps-I'm thinking of using sapele instead of the $$$Bruynzeel.
    • adharvey2
      Russell, I ve been confronting the same issue with Elon Jessup. Soon as I read that bit in the plans I went and bought all of my 1/2 okoume ply and 3/4 for
      Message 2 of 5 , Dec 16, 2005
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        Russell, I've been confronting the same issue with Elon Jessup. Soon
        as I read that bit in the plans I went and bought all of my 1/2"
        okoume ply and 3/4 for the bottom. That gives you about the same
        weight as the Cypress. Then we had a discussion on this site about
        lightening the design with 3/8 ply for the sides and 1/2 for the
        bottom. But I'm not convinced that a 4 1/2' wide frameless 1/2 sheet
        bottom would be a very satisfactory replacement for a cross planked
        bottom. And I have my doubts about the 3/4 ply as well. Also I'm with
        you on not wanting to change the boats weight without a good reason.
        On the other hand, there are a lot of articles and books out there
        that preach lightness - especially for flat bottomed boats! And
        there's no doubt you COULD build her lighter.
        I also have been thinking that a double bottom might be way to go,
        but what thickness? I hope you can sort it out for both of us. You
        might look at the numerous earlier posts on this subject.
        Andrew Harvey

        --- In AtkinBoats@yahoogroups.com, "rljssn" <rljssn@y...> wrote:
        >
        > I've been trying to work out which skiff and what material for too
        > long. I like these old skiffs but the traditional woods in decent grain
        > are turning out just as expensive as the marine plywood in my area. In
        > the description story on Jessup it mentions 1/2" rotary cut Bruynzeel
        > plywood as a substitute. Is there any more information or a precedent
        > from boats built as to how to make this substitution? Is there anything
        > in the scantilings table about the planking? 1/2" ply in the sides and
        > a double thickness on bottom maybe?
        >
        > I think I can live with the non-traditional materials but I don't want
        > to lighten this design and change the load waterline characteristics.
        >
        > thanks for all the great advice,
        > at least I've got a favorite skiff picked out.-Russell
        >
        > ps-I'm thinking of using sapele instead of the $$$Bruynzeel.
        >
      • John B. Trussell
        Bear in mind that free advise may not be worth more than it costs, but... A major advantage of cross planked skiffs is that the bottom is stiff and does not
        Message 3 of 5 , Dec 16, 2005
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          Bear in mind that free advise may not be worth more than it costs, but...

          A major advantage of cross planked skiffs is that the bottom is stiff and
          does not require any framing. (A disadvantage is that unless you get very
          crafty, cross planked boats dry out on a trailer and leak horribly. They
          need to be kept in the water.) A fairly obvious solution is to plank with
          plywood. However, plywood is fairly heavy (at least compared to cedar) and
          it is a fairly limp material. If you substitute plywood for cedar by
          weight, the bottom will flex. Two options are to increase thickness of the
          plywood (building a heavier boat) or to beef up the framing.

          I am currently contemplating plans from a New Zealand designer for a flat
          bottomed plywood skiff about 6 inches shorter than Elton Jessup. It is all
          in metric, of course, but the approximate scantlings are:

          Planking 6mm--1/4" plywood
          Keelson 60mmx20mm, roughly 1"x3"
          Sister keelson 40mmx20mm, roughly 1"x2"
          Frames under each thwart--roughly 3 ft apart--60mmx20mm
          Keel 40mmx20mm

          The sides are lapstrake with two strakes (this looks good and effectively
          doubles the thickness of the sides where the strakes overlap. In addition,
          there is a 10mmx30mm (1/2x1 1/2) half round molding strip at the outside
          bottom of the top strake and a 20mmx40mm gunwale.

          I think this will produce a fairly light, stiff boat.

          I have used Bruynzeel and like it very much. Published information on
          Sapele is that it is heavier and stiffer than Bruynzeel, but I have no first
          hand experience with it. I recently built a boat using MDO plywood. This
          is the same stuff used to make highway signs and obviously Highway
          Departments have more clout with plywood manufacturers than boatbuilders.
          It is awfully nice stuff, but is normally available only in 3/8" and 1/2".
          You might want to consider this.

          Good luck.

          John T
          ----- Original Message -----
          From: "rljssn" <rljssn@...>
          To: <AtkinBoats@yahoogroups.com>
          Sent: Friday, December 16, 2005 1:36 PM
          Subject: [AtkinBoats] Elon Jessup plywood


          > I've been trying to work out which skiff and what material for too
          > long. I like these old skiffs but the traditional woods in decent grain
          > are turning out just as expensive as the marine plywood in my area. In
          > the description story on Jessup it mentions 1/2" rotary cut Bruynzeel
          > plywood as a substitute. Is there any more information or a precedent
          > from boats built as to how to make this substitution? Is there anything
          > in the scantilings table about the planking? 1/2" ply in the sides and
          > a double thickness on bottom maybe?
          >
          > I think I can live with the non-traditional materials but I don't want
          > to lighten this design and change the load waterline characteristics.
          >
          > thanks for all the great advice,
          > at least I've got a favorite skiff picked out.-Russell
          >
          > ps-I'm thinking of using sapele instead of the $$$Bruynzeel.
          >
          >
          >
          >
          >
          >
          > No flaming, cursing, politics, religion or public mopery. Please be
          > polite.
          >
          > If you set out to build an Atkin boat, please do not modify the plans. If
          > you stray from the plans you do so at your own risk and Atkin & Co. will
          > take no responsibility for the performance of the resulting boat.
          >
          > The current Atkin boat plans catalog is online at
          > <http://www.atkinboatplans.com/>
          >
          >
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        • JJ Johnson
          Before I say anything, just remember we are NOT supposed to change the Atkin designs structurely.. Somewhere in all my books and articles I have the formulas
          Message 4 of 5 , Dec 17, 2005
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            Before I say anything, just remember we are NOT supposed to change
            the Atkin designs structurely..

            Somewhere in all my books and articles I have the formulas on how to
            do this. The problem is I can not remember who wrote the
            article/book. It might have been David Gerr, or Jim Michalak, or Ted
            Brewer or who knows, I just do not remember.

            Also many of the older designs are designed and built to survive oh-
            my-god situations. Which is not saying that this wrong, it is
            absolutely right! Just that, in a small pond or stream, it is not
            necessary.

            However if you do make structural changes you should redo the frame
            spaceing (read stringers and frames) to support the skin you decide
            to use, AND, the speed at which you want to operate your boat, AND
            its designed displacement. The faster or heavyer the boat, the
            stronger the framing/skin combination must be to stop oil-canning and
            structural failure. This may be done by increaseing the skin
            thickness without changing the frame spaceing, or by decreasing the
            skin thickness and frame spaceing. The latter will normally result in
            a lighter, less expensive boat that needs ballast. So why not take
            the savings and build with the better materials, add ballast in the
            way of personal gear and go cruising... hehehehe

            JJ








            --- In AtkinBoats@yahoogroups.com, "adharvey2" <adharvey@m...> wrote:
            >
            > Russell, I've been confronting the same issue with Elon Jessup. Soon
            > as I read that bit in the plans I went and bought all of my 1/2"
            > okoume ply and 3/4 for the bottom. That gives you about the same
            > weight as the Cypress. Then we had a discussion on this site about
            > lightening the design with 3/8 ply for the sides and 1/2 for the
            > bottom. But I'm not convinced that a 4 1/2' wide frameless 1/2 sheet
            > bottom would be a very satisfactory replacement for a cross planked
            > bottom. And I have my doubts about the 3/4 ply as well. Also I'm
            with
            > you on not wanting to change the boats weight without a good reason.
            > On the other hand, there are a lot of articles and books out there
            > that preach lightness - especially for flat bottomed boats! And
            > there's no doubt you COULD build her lighter.
            > I also have been thinking that a double bottom might be way to
            go,
            > but what thickness? I hope you can sort it out for both of us. You
            > might look at the numerous earlier posts on this subject.
            > Andrew Harvey
            >
            > --- In AtkinBoats@yahoogroups.com, "rljssn" <rljssn@y...> wrote:
            > >
            > > I've been trying to work out which skiff and what material for
            too
            > > long. I like these old skiffs but the traditional woods in decent
            grain
            > > are turning out just as expensive as the marine plywood in my
            area. In
            > > the description story on Jessup it mentions 1/2" rotary cut
            Bruynzeel
            > > plywood as a substitute. Is there any more information or a
            precedent
            > > from boats built as to how to make this substitution? Is there
            anything
            > > in the scantilings table about the planking? 1/2" ply in the
            sides and
            > > a double thickness on bottom maybe?
            > >
            > > I think I can live with the non-traditional materials but I don't
            want
            > > to lighten this design and change the load waterline
            characteristics.
            > >
            > > thanks for all the great advice,
            > > at least I've got a favorite skiff picked out.-Russell
            > >
            > > ps-I'm thinking of using sapele instead of the $$$Bruynzeel.
            > >
            >
          • John Kohnen
            ... If your Elon Jessup is going to live on a trailer using a plywood bottom, at least, is the best way to go. For some time I ve been meaning to put something
            Message 5 of 5 , Dec 23, 2005
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              On Fri, 16 Dec 2005 10:36:10 -0800, rljssn wrote:

              > I've been trying to work out which skiff and what material for too
              > long. I like these old skiffs but the traditional woods in decent grain
              > are turning out just as expensive as the marine plywood in my area. In
              > the description story on Jessup it mentions 1/2" rotary cut Bruynzeel
              > plywood as a substitute. Is there any more information or a precedent
              > from boats built as to how to make this substitution? Is there anything
              > in the scantilings table about the planking? 1/2" ply in the sides and
              > a double thickness on bottom maybe?
              > ...

              If your Elon Jessup is going to live on a trailer using a plywood bottom,
              at least, is the best way to go.

              For some time I've been meaning to put something together showing what
              scantlings the Atkins used when designing for plywood, to help those who
              want to convert to that kind of planking. I finally got a start in that
              direction, and here are some examples of plywood planked skiffs:

              Katelyn
              14' 3" x 4' 10" x 3' 8 1/4" bottom width
              Sides and bottom 3/8" plywood
              Keel batten 3/4" x 8" plywood
              3/4" x 2 1/2" oak bottom frames on 30" centers

              Sunshine
              17' 1 1/2" x 6' x 4' 9" bottom width
              Sides and bottom 3/8" plywood
              Keel batten 3/4" x 8" oak
              3/4" x 2 1/4" oak bottom frames on 32" centers

              Willy Winship as built by The Boatman
              13' 9" x 4' 10" x 3' 6 1/8" bottom width
              Sides 3/8" plywood
              Bottom 1/2" plywood
              Two 3/4" x 2" white cedar keelsons plus two 1/2" x 2" oak bottom skids
              Frames on about 29" centers

              Jasper
              14' 2" x 4' x 3' 1 1/2" bottom width
              Sides 1/2" plywood
              Bottom 5/8" plywood
              Keel batten 3/4" x 6" pine
              No bottom frames

              The Boatman Willy Winship was obviously overbuilt! I don't know if they
              got those scantlings from John, or if they thought them up themselves.

              Bottom frames are horrible to live with in a flat-bottom skiff! :o( If you
              must use them, make the limbers big, and put limbers both at the chines
              and next to the keelson, otherwise you'll have a heck of a time keeping
              the boat clean and dry. Don't ask how I know... <g> If I was building an
              Atkin skiff I'd go with the cross-planked style bottom, but using plywood
              sheets laid crosswise. I think the scantlings for Jasper are a bit heavy
              -- I'd use 3/8" ply on the sides and 1/2" ply on the bottom for a skiff in
              the 14-16' size range. Elon Jessup would probably be fine with no bottom
              frames and a 1/2" bottom and 3/8" sides (I'd do the lapstrake planks in
              plywood), but a 5/8" plywood bottom might be better for heavy use.

              --
              John <jkohnen@...>
              No man will be a sailor who has contrivance enough to get
              himself into jail; for being in a ship is being in a jail, with
              the chance of being drowned... A man in jail has more room,
              better food, and commonly better company. <Samuel Johnson>
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