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Re: confusion,

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  • graeme19121984
    No need to go into just why that shape is... leave that mixed-up critic to wallow. Now, if they d been referencing waste disposal barges that carry the stuff,
    Message 1 of 7 , Jan 3, 2010
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      No need to go into just why that shape is... leave that mixed-up critic to wallow. Now, if they'd been referencing waste disposal barges that carry the stuff, & similar ...or subs, then they'd still be mixed up somewhat -- but it might be worth a try explaining it to 'em ;-D

      Search Jim Michalak's newsletter a year or so back. Someone built one of his larger cabined shanty/scow designs; not a particularly light boat either; and meant for small outboard power. They did not build to plan. They did what Bolger mentions for the brick stern, and reported it as being ok under sail. JM wrote an article or two on it as I recall. He analysed it in various ways (Savitsky et al, etc, Hullforms), and it more or less confounded him as the models predominantly confirmed better performance from the flat-run/square-transomed not-to-plan bottom. Conventional knowledge says it just never should!

      There are a number of possible factors that working jointly and seperately may allow this bottom to deliver the performance on low power. Some might be: trim, heel, WLL, water depth, prismatic form, depth to beam ratio, wetted planing surface, and PCB's (Hickman?) "hover" effect.

      I suspect the design envelope for these factors to work optimally is a tight one, yet a sub-optimal design may still surprise as I believe PCB mused on by his comment about the altered Brick stern increase in capacity. "Capacity" not so much in the sense of 'displacement', but also in the sense of 'capacity to perform' (here on the same light displacement), or by stretching the original envelope.

      Graeme



      --- In bolger@yahoogroups.com, John Bell <yonderman@...> wrote:
      >
      > The designer was chided "Even a turd is pointy at both ends..."
      >
      > Submerged transoms create a lot of turbulence and therefore drag. Sailboats
      > suffer a lot when there's a lot of drag. Build it as designed, or better yet
      > build a PDR!
      >
      > On Fri, Jan 1, 2010 at 9:23 PM, Christopher C. Wetherill <
      > wetherillc@...> wrote:
      >
      > >
      > >
      > > I do not recall the name or the year, but there was a contender to defend
      > > the America's cup in the '70s that had a flat stern below the water line.
      > > The idea was that the effective water line was thereby longer than the
      > > actual. It failed miserably. I think it only works when the hull planes.
      > >
      > > V/R
      > > Chris
      > >
      > >
      > >
      > > Mark Albanese wrote:
      > >
      > >
      > >
      > > Morten Olesen at Boatplans.dk used to show a couple of sailboat cruisers
      > > with square sterns, though they weren't so successful that he still promotes
      > > them.
      > >
      > > It would be hard to gauge a difference in speed at Brick's scale. The
      > > regular stern is rockered so high the boat will surely feel steadier with it
      > > run back. For sailing, the regular shape is prudent, not to say traditional.
      > > For power alone or as a tiny motorsailer, straight back is sure to work.
      > >
      > > Mark
      > >
      > >
      > > On Jan 1, 2010, at 3:59 PM, Robert wrote:
      > >
      > >
      > > It is uncertain to me that if the bottom were run back to a perfectly
      > > rectangular stern(with the bottom of the transom in the water), as to
      > > whether the sailing performance of the Brick would be degraded. I agree that
      > > the capacity will be increased because of the increased wetted surface. Is
      > > he suggesting that this could be done with no degradation to the boat's
      > > sailing ability?
      > >
      > > I have never seen a sailboat where the transom sits in the water, as a
      > > fishing boat does. The aft part of the hull is always tapered upward to the
      > > transom, and the transom is out of the water. There must be a reason why.
      > > but I can't imagine why.
      > >
      > > Would someone clarify this for me? Thanks.
      > >
      > > Robert
      > > Niagara Falls, Ontario
    • graeme19121984
      ... One must remember that the advantage of the swept (up)(sailing) hull is probably no real advantage since it happens at an extreme trim that only a land
      Message 2 of 7 , Jan 4, 2010
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        > JM wrote an article or two on it as I recall...


        "One must remember that the advantage of the swept (up)(sailing)
        hull is probably no real advantage since it happens at an extreme
        trim that only a land lubber would accept." "I was afraid of
        that. Only about 16 pounds drag at 5 knots, less again than the
        sailing hull. Well, I don't believe it. What else can I
        say." "Well, Bolger is right again - you have to build two real
        hulls and test. Then I'll believe it." - Jim Michalak.


        http://www.jimsboats.com/2007/15jul07.htm

        http://www.jimsboats.com/2007/15aug07.htm

        Graeme


        --- In bolger@yahoogroups.com, "graeme19121984" <graeme19121984@...> wrote:
        >
        >
        >
        >
        >
        >
        > No need to go into just why that shape is... leave that mixed-up critic to wallow. Now, if they'd been referencing waste disposal barges that carry the stuff, & similar ...or subs, then they'd still be mixed up somewhat -- but it might be worth a try explaining it to 'em ;-D
        >
        > Search Jim Michalak's newsletter a year or so back. Someone built one of his larger cabined shanty/scow designs; not a particularly light boat either; and meant for small outboard power. They did not build to plan. They did what Bolger mentions for the brick stern, and reported it as being ok under sail. JM wrote an article or two on it as I recall. He analysed it in various ways (Savitsky et al, etc, Hullforms), and it more or less confounded him as the models predominantly confirmed better performance from the flat-run/square-transomed not-to-plan bottom. Conventional knowledge says it just never should!
        >
        > There are a number of possible factors that working jointly and seperately may allow this bottom to deliver the performance on low power. Some might be: trim, heel, WLL, water depth, prismatic form, depth to beam ratio, wetted planing surface, and PCB's (Hickman?) "hover" effect.
        >
        > I suspect the design envelope for these factors to work optimally is a tight one, yet a sub-optimal design may still surprise as I believe PCB mused on by his comment about the altered Brick stern increase in capacity. "Capacity" not so much in the sense of 'displacement', but also in the sense of 'capacity to perform' (here on the same light displacement), or by stretching the original envelope.
        >
        > Graeme
        >
        >
        >
        > --- In bolger@yahoogroups.com, John Bell <yonderman@> wrote:
        > >
        > > The designer was chided "Even a turd is pointy at both ends..."
        > >
        > > Submerged transoms create a lot of turbulence and therefore drag. Sailboats
        > > suffer a lot when there's a lot of drag. Build it as designed, or better yet
        > > build a PDR!
        > >
        > > On Fri, Jan 1, 2010 at 9:23 PM, Christopher C. Wetherill <
        > > wetherillc@> wrote:
        > >
        > > >
        > > >
        > > > I do not recall the name or the year, but there was a contender to defend
        > > > the America's cup in the '70s that had a flat stern below the water line.
        > > > The idea was that the effective water line was thereby longer than the
        > > > actual. It failed miserably. I think it only works when the hull planes.
        > > >
        > > > V/R
        > > > Chris
        > > >
        > > >
        > > >
        > > > Mark Albanese wrote:
        > > >
        > > >
        > > >
        > > > Morten Olesen at Boatplans.dk used to show a couple of sailboat cruisers
        > > > with square sterns, though they weren't so successful that he still promotes
        > > > them.
        > > >
        > > > It would be hard to gauge a difference in speed at Brick's scale. The
        > > > regular stern is rockered so high the boat will surely feel steadier with it
        > > > run back. For sailing, the regular shape is prudent, not to say traditional.
        > > > For power alone or as a tiny motorsailer, straight back is sure to work.
        > > >
        > > > Mark
        > > >
        > > >
        > > > On Jan 1, 2010, at 3:59 PM, Robert wrote:
        > > >
        > > >
        > > > It is uncertain to me that if the bottom were run back to a perfectly
        > > > rectangular stern(with the bottom of the transom in the water), as to
        > > > whether the sailing performance of the Brick would be degraded. I agree that
        > > > the capacity will be increased because of the increased wetted surface. Is
        > > > he suggesting that this could be done with no degradation to the boat's
        > > > sailing ability?
        > > >
        > > > I have never seen a sailboat where the transom sits in the water, as a
        > > > fishing boat does. The aft part of the hull is always tapered upward to the
        > > > transom, and the transom is out of the water. There must be a reason why.
        > > > but I can't imagine why.
        > > >
        > > > Would someone clarify this for me? Thanks.
        > > >
        > > > Robert
        > > > Niagara Falls, Ontario
        >
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