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59418Re: Water Ballasted Chebacco

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  • mcdennyw
    Jan 12, 2009
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      Graeme,

      According to my Freeship model, the unballasted Chebacco (this is the
      lapstrake 19' offsets) righting moment goes negative at 93 degrees of
      heel. Water ballasted as above has a RM of 950 ft-lbs at 93 degrees,
      does not go negative until 107 degrees. This ignores any flotational
      aspects of rig and assumes cockpit seats are water tight.

      Max RM of unballasted boat is 1200 ft-lbs from 30 to 60 degrees.
      Ballasted boat has RM of 2300 at 30, max of 2600 between 45 and 60
      degrees.

      If the boat were at 180 degrees, exactly turtle, I don't know it it
      would come back upright or not. I'm pretty sure most all unballasted
      boats are stable at 180 degrees.

      For sure the ballasted boat would be a lot less likely to get upside
      down in the first place.

      Denny


      >
      > Wost case (Water ballast caught Bolger out once or twice): At what
      > angle does the RM curve go negative - masts and all? Is there any
      > bouyant volume of a size that may concern at or near the same
      height
      > as the water ballast -- eg under cockpit seats? Consider on beam
      ends
      > wave rocking too.
      >
      > I'm just cautious that the ballast for extra RM for improved
      sailing
      > in exhilarating conditions doesn't cause a boat that might
      otherwise
      > rest on her side when knocked down to go... right over.
      >
      > Red Zinger, Beachcat, Chebaccos (mostly), etc, are the
      > daysailing/cruising alternatives for those who want no messing with
      > lead pouring... Well, certainly Beachcat has been described as such
      > by PB&F. The OSTAR RACER #459 has a deep pivoting centreboard with
      > distal, auto-trimming, winged ballast.
      >
      > Graeme
      > (PS Talking of ostar and sharpie keels, and RM. gee, I can't
      believe
      > #543 isn't in the database. sure it were once. will take a look
      later
      > off-line)
      >
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