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Beachcat #589 & free flooding keel (was Re: Water Ballasted Chebacco)

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  • graeme19121984
    I missed that. Charles posted there was info about Big Tortoise in Instant Boatbuilding with Dynamite Payson . I browsed on to Catfish, a Chebacco spin-off,
    Message 1 of 26 , Feb 6, 2009
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      I missed that.

      Charles' posted there was info about Big Tortoise in "Instant
      Boatbuilding with Dynamite Payson". I browsed on to Catfish, a
      Chebacco spin-off, and, blow me down, in the first short paragraph
      Payson describes the self-righting and light trailering gained from
      the free flooding keel under this design. I mean - it's the first
      thing he jumps in at to describe!

      PB&F have described aspects of the high and wide decks of Beachcat
      that make for ease of mind in potential knock-down sailing
      conditions. They mention the good ability of the salient keel in
      thinner water than the centreboard of the upgrade plans can handle.
      PCB seems to prefer the salient keel on Beachcat for himself, but to
      my knowledge they have never elaborated on the benefits of the keel
      being free flooding. Never published on this design aspect - I
      thought it solid. This free-flooding/slow-draining is what adds so
      much to Micro, supplemental to the lead ballast, in self-righting
      immediately following a knockdown all the way to a beam ends attitude
      where the keel is lifted above the water and before the internal
      water has had time to drain out. The cross section of Beachcat
      probably means that the flooded keel begins to lift above the water
      and have a righting effect at more intermediate angles of heel than
      on Micro, and keeps righting moment fairly positive as heeling
      progresses for some arc beyond 90deg.

      In a certain published vignette, that although un-named could only
      have featured cruising aboard an original Catfish, a prominent Aussie
      designer/builder didn't mention the designed benefits of freely
      flooding the Catfish keel. Has Mr Payson got his wires crossed?

      Graeme



      --- In bolger@yahoogroups.com, "mcdennyw" <dwolfe@...> wrote:
      >
      > Graeme,
      >
      > I modelled the full keel 246# lead ballast design
      (Bolger's 'Cruiser'
      > version) and the RM is right in between the no ballast and water
      > ballast designs. At 20 degrees the 246# lead gives RM of 1393 ft-
      > lbs. No ballast RM is 1041, water ballast RM is 1883.
      >
      > The vertical CG of the water ballasted boat is 2.5" lower than the
      > one with lead ballast. The lead is lower but only half the weight.:
      > >
      > > Denny,
      > >
      > > that sounds all to be good. Great.
      > >
      > > I wonder how much different are the figures for the lead
      ballasted
      > > keel version. They'd cost a little extra in the 246lbs to
      trailer,
      > > and another 6 inches of draft. I wonder if that lead ballast keel
      > > might add a bit more than the 500lbs internal water ballast to
      > > initial stability, but then not to final stability?
      > >
      > > Graeme
      > >
      >
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