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Presto Cruiser

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  • Will Parkes
    Did PCB complete plans for the Presto Cruiser design in BWAOM? If so, does anyone know if it is all strip planked or is any ply used in the construction? Over
    Message 1 of 7 , Jan 31, 2007
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      Did PCB complete plans for the Presto Cruiser design in BWAOM? If so,
      does anyone know if it is all strip planked or is any ply used in the
      construction?

      Over the weekend, in the presence of a naval architect, I was
      discussing sharpies with some fellow Bolger fans. We compared a number
      of hard chine sharpie designd, like Skillygallee, with more round edged
      designs like Karl Stambaugh's Trailer Sailer 24. Stambaugh uses ply on
      the sides and bottoms and strip planking on the corners. Some opined
      that the additional work involved in the strip planking wasn't worth
      what was thought to be a small gain in performance.

      We also compared the square sided sharpies (AS-29 etc) with those with
      more flair from Howard Chappelle as well as PCB. The flair averaged
      about 23 degrees from the vertical amidships. Does anyone have a view
      about the value of sharpie flair?
    • Peter Lenihan
      ... Does anyone have a view ... Seeing as sharpies,as we know them, apparently evolved from work boats, I can only imagine that any flair would serve to
      Message 2 of 7 , Jan 31, 2007
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        --- In bolger@yahoogroups.com, "Will Parkes" <icusa98@...> wrote:
        Does anyone have a view
        > about the value of sharpie flair?

        Seeing as sharpies,as we know them, apparently evolved from work
        boats, I can only imagine that any flair would serve to increase the
        boats carrying capacity and thus its' profitablity.That flair also
        helps in knocking down spray when the boats are motor driven, may be a
        secondary reason.


        Sincerely,

        Peter "The Guessing Wiz" Lenihan.......
      • Wesley Cox
        I m no naval architect, but I am obsessed with boats and boat design and not being an expert doesn t generally keep me from forming and voicing opinions :).
        Message 3 of 7 , Jan 31, 2007
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          I'm no naval architect, but I am obsessed with boats and boat design and not being an expert doesn't generally keep me from forming and voicing opinions :).

          I've built a significant number of scale models of my own designs, to compare bath tub "performance" of different hull features. I've found a major difference in secondary stability between any single chine design, flare or not, and any multi-chine design. Even a second chine makes a world of difference compared to just one. Flare with a single chine presents a flat plane to the water sooner than a box, resisting further tip. On the other hand, flare reduces the extent of tip possible before the gunnel is under water. With a box with no flare, the boat must tip 90 degrees before the gunnel is in the water. With 23 degrees of flare, if you mean 23 degrees down from vertical (surely not 23 degress up from horizontal?), 67 degrees of boat tip will put the gunnel in the water. There's much more resistance to tipping from horizontal than with a box, though. The box has 23 degrees more to give, but the first part of the tip has little resistance imparted by its geometry relative to the boat with flared sides. I haven't studied it mathematically, but from my own empirical experiments, I think given the same bottom width and side height, measured vertically, a boat with flare will have better secondary stability than a box. Some of us think flare is also more salty looking (please don't hit me, I think Bolger is awesome).

          Someone will correct me with figures and examples if I'm wrong, I'm sure. To me personally, it's a moot point. In the size of boats to which I gravitate and for the cold local water, secondary stability is of keen importance and I don't seriously consider single chine boats anymore, at least not without a great deal of ballast, which also isn't my style. My scale model, "Me", has to do really outrageous things to get wet in a boat with even 2 chines. A comparably sized single chine boat requires substantial ballast to even come close to the same (secondary) stability. Otherwise, "Me" has to remain low and very close to the center line at all times or end up at the bottom of the tub in the blink of an eye. Of course, "Me" is very rigid and uncoordinated, which makes single chines look worse than they are in real life, but the tests are of the geometry of the hulls, not the athletic ability of "Me".

          What specific performance criteria are you using to compare hard chine versus not and flare versus box?


          ----- Original Message -----
          From: Will Parkes
          To: bolger@yahoogroups.com
          Sent: Wednesday, January 31, 2007 6:10 PM
          Subject: [bolger] Presto Cruiser


          Did PCB complete plans for the Presto Cruiser design in BWAOM? If so,
          does anyone know if it is all strip planked or is any ply used in the
          construction?

          Over the weekend, in the presence of a naval architect, I was
          discussing sharpies with some fellow Bolger fans. We compared a number
          of hard chine sharpie designd, like Skillygallee, with more round edged
          designs like Karl Stambaugh's Trailer Sailer 24. Stambaugh uses ply on
          the sides and bottoms and strip planking on the corners. Some opined
          that the additional work involved in the strip planking wasn't worth
          what was thought to be a small gain in performance.

          We also compared the square sided sharpies (AS-29 etc) with those with
          more flair from Howard Chappelle as well as PCB. The flair averaged
          about 23 degrees from the vertical amidships. Does anyone have a view
          about the value of sharpie flair?






          [Non-text portions of this message have been removed]
        • craig o'donnell
          ... A little bit more spray suppression in some cases. In others, it doesn t matter much. Tradition. Pulling gear straight up means you don t drag it on up the
          Message 4 of 7 , Jan 31, 2007
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            >We also compared the square sided sharpies (AS-29 etc) with those with
            >more flair from Howard Chappelle as well as PCB. The flair averaged
            >about 23 degrees from the vertical amidships. Does anyone have a view
            >about the value of sharpie flair?

            A little bit more spray suppression in some cases. In others, it doesn't
            matter much. Tradition. Pulling gear straight up means you don't drag it on
            up the side of the boat. Siumple bending of planks creates some flare and
            rocker... (Commordore Munroe's Proa is a prime example of this).

            Also, if you're loading a boat with oysters, with flare, the more you
            loads, the slower the freeboard decreases, sez popeye the sailor man ...
            --
            Craig O'Donnell
            Sinepuxent Ancestors & Boats
            <http://freepages.genealogy.rootsweb.com/~fassitt/>
            The Proa FAQ <http://boat-links.com/proafaq.html>
            The Cheap Pages <http://www.friend.ly.net/~dadadata/>
            Sailing Canoes, Polytarp Sails, Bamboo, Chinese Junks,
            American Proas, the Bolger Boat Honor Roll,
            Plywood Boats, Bamboo Rafts, &c.
            _________________________________

            -- Professor of Boatology -- Junkomologist
            -- Macintosh kinda guy
            Friend of Wanda the Wonder Cat, 1991-1997.
            _________________________________

            [Non-text portions of this message have been removed]
          • Kristine Bennett
            Wesley there is something else to add to the mix as well, ONe, is styling As in how the boat looks. Two. being simple to build and fit panals together. If the
            Message 5 of 7 , Jan 31, 2007
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              Wesley there is something else to add to the mix as
              well, ONe, is styling As in how the boat looks. Two.
              being simple to build and fit panals together.

              If the box has a lot of beam its hard to flip them
              over. Look at the power barges of WW2 that hauled
              cargo up and down the west coast and across the gulf
              of Alaska for years.

              I know you are talking about sailboats but still it
              does apply.

              Krissie
              --- Wesley Cox <inspirfe@...> wrote:

              > I'm no naval architect, but I am obsessed with boats
              > and boat design and not being an expert doesn't
              > generally keep me from forming and voicing opinions
              > :).
              >
              > I've built a significant number of scale models of
              > my own designs, to compare bath tub "performance" of
              > different hull features. I've found a major
              > difference in secondary stability between any single
              > chine design, flare or not, and any multi-chine
              > design. Even a second chine makes a world of
              > difference compared to just one. Flare with a
              > single chine presents a flat plane to the water
              > sooner than a box, resisting further tip. On the
              > other hand, flare reduces the extent of tip possible
              > before the gunnel is under water. With a box with
              > no flare, the boat must tip 90 degrees before the
              > gunnel is in the water. With 23 degrees of flare,
              > if you mean 23 degrees down from vertical (surely
              > not 23 degress up from horizontal?), 67 degrees of
              > boat tip will put the gunnel in the water. There's
              > much more resistance to tipping from horizontal than
              > with a box, though. The box has 23 degrees more to
              > give, but the first part of the tip has little
              > resistance imparted by its geometry relative to the
              > boat with flared sides. I haven't studied it
              > mathematically, but from my own empirical
              > experiments, I think given the same bottom width and
              > side height, measured vertically, a boat with flare
              > will have better secondary stability than a box.
              > Some of us think flare is also more salty looking
              > (please don't hit me, I think Bolger is awesome).
              >
              > Someone will correct me with figures and examples if
              > I'm wrong, I'm sure. To me personally, it's a moot
              > point. In the size of boats to which I gravitate
              > and for the cold local water, secondary stability is
              > of keen importance and I don't seriously consider
              > single chine boats anymore, at least not without a
              > great deal of ballast, which also isn't my style.
              > My scale model, "Me", has to do really outrageous
              > things to get wet in a boat with even 2 chines. A
              > comparably sized single chine boat requires
              > substantial ballast to even come close to the same
              > (secondary) stability. Otherwise, "Me" has to
              > remain low and very close to the center line at all
              > times or end up at the bottom of the tub in the
              > blink of an eye. Of course, "Me" is very rigid and
              > uncoordinated, which makes single chines look worse
              > than they are in real life, but the tests are of the
              > geometry of the hulls, not the athletic ability of
              > "Me".
              >
              > What specific performance criteria are you using to
              > compare hard chine versus not and flare versus box?
              >




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            • John and Kathy Trussell
              Before PCB, the expert on sharpies was Howard I Chapelle. The original working sharpies were cheap, shallow draft, were used for tonging,and had to carry huge
              Message 6 of 7 , Feb 1, 2007
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                Before PCB, the expert on sharpies was Howard I Chapelle.

                The original working sharpies were cheap, shallow draft, were used for tonging,and had to carry huge loads. Chapelle says they generally had between 3 1/2" and 4" of flare for each foot of depth. Since many sharpies had nearly vertical stems, there was often less flare forward and more aft. Chapelle states that less flare was used for speed and more for seaworthiness.

                A basic problem with sharpies is that water flows at one speed under the bottom and at a different speed along the side. The difference in speed creates a pressure differential and water tries to move over the chine to equalize the pressure. This movement takes the form of edies and these create drag, slowing the boat. One effort to reduce edies is to match the curve of the side to the curve of the bottom, thus reducing the difference in speedof thewater on the bottom and side, the pressure differential, and the edies. Another approach is the 'presto' sharpie with rounded chines. These provide a smoother course for the equalization of pressure and, in theory, reduce drag. Jim Michalak has several designs in which he cuts the corner off the chine and replaces it with a plywood panel. I have one and it seems to sail fine, but without a similiar sized sharpie for comparison, I can't state that it works better (or worse) than a more normal sharpie.

                If I were building PCB's Presto, I'd build the bottom and sides of plywood and strip plank the chines, fiberglassing the whole thing. I'm to old to tackle a boat building project this size, but the 'Presto Sharpie' sure is a pretty boat.

                John T
                ----- Original Message -----
                From: Will Parkes
                To: bolger@yahoogroups.com
                Sent: Wednesday, January 31, 2007 7:10 PM
                Subject: [bolger] Presto Cruiser


                Did PCB complete plans for the Presto Cruiser design in BWAOM? If so,
                does anyone know if it is all strip planked or is any ply used in the
                construction?

                Over the weekend, in the presence of a naval architect, I was
                discussing sharpies with some fellow Bolger fans. We compared a number
                of hard chine sharpie designd, like Skillygallee, with more round edged
                designs like Karl Stambaugh's Trailer Sailer 24. Stambaugh uses ply on
                the sides and bottoms and strip planking on the corners. Some opined
                that the additional work involved in the strip planking wasn't worth
                what was thought to be a small gain in performance.

                We also compared the square sided sharpies (AS-29 etc) with those with
                more flair from Howard Chappelle as well as PCB. The flair averaged
                about 23 degrees from the vertical amidships. Does anyone have a view
                about the value of sharpie flair?







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              • mkriley48
                lets just see what the extra weight of making the bottom and hull sides of steel. Bottom has plate of 1/2 10 x 24 = 2000lbs will make 1/4 bottom for 2000 lbs
                Message 7 of 7 , Feb 2, 2007
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                  lets just see what the extra weight of making the bottom and hull
                  sides of steel. Bottom has plate of 1/2 10'x 24'= 2000lbs will make
                  1/4" bottom
                  for 2000 lbs minus the weight of the original bottom so a net gain in
                  reducing weight. hull sides of 1/8" steel{2000lbs?} minus the weight
                  of the original sides and the weight saved on the bottom all else done
                  to the original plans in wood and fastened to the hull with bolts,
                  onto tabs welded to the hull. I think weight gain would be minimal.
                  can someone run numbers on the weight of the plywood hull and the
                  steel hull skin only. No need for steel internals, if the wood
                  structure was good enough for a weaker ply hull it will be fine for a
                  stronger steel one.
                  This kind of wood deck and house with steel hull has been used for
                  over 100 years with success <starof india>
                  can someone run the numbers?
                  thanks
                  mike
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