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55996Re: Martha Jane on Ebay

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  • martha2001au
    Nov 6, 2007
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      Hi Graeme,
      Good to hear from you again! As you can tell I'm still pining after
      a Martha Jane, got distracted though and built a Surf, then work,
      family,bills, you know the drill. I still have all your letters on
      building and rigging advice on hand ready to go.

      From my reading of the upgrades, the 500lb shoe is in addition to
      the water ballast. I liked your idea of adding extra water ballast -
      do you know how much extra weight in water was added by your mods?
      Also my original uprades don't mention and storage ability for the
      cockpit seats.

      I must admit I wasn't fond of the look of the sponsons at first, but
      I am getting used to them. The way I'm thinking at the moment,If I
      ever get to build I'd go with the aluminium mast, extra water
      ballast, and sponsons. I think she's heavy enough to trailer
      without an extra 500lb of dead weight.

      Interesting theory on having free flooding seats - as long as theres
      enough reserve bouyancy in the sponsons.

      All the best,

      Col


      ups.com, "graeme19121984" <graeme19121984@...> wrote:
      >
      > Searching around the net for any newer info on Martha Jane(s) I
      > again came across the Jim Michalak Newsletter page November 1,
      2000
      > http://members.fortunecity.com/duckworks/2000/1101/
      >
      > I don't lightly differ with an opinion of Mr Michalak, but it
      struck
      > me that a particular warning he gives for boats generally may not
      > apply for the example he gives of Bob Archibald's then recently
      > acquired Martha Jane.
      >
      > Take a look at the third sketch above the caption "KEEP SEATS
      > WATERTIGHT!" Looking at JM's styleized sketch of Martha Jane it
      > occurs to me that water tight cockpit seats just might be the
      factor
      > that resulted in some early Martha Janes rolling over much further
      > than 90degrees after a knockdown. Consider that a waterballast
      tank
      > has a volume of about 4 cubic feet and a cockpit seat encloses a
      > volume of what, say, 5 to 6 cubic feet.
      >
      > Consider that once the Martha Jane was knocked to its beam ends
      > there would be 250lbs of water ballast now up in the air and
      waving
      > about, and that there would be a significant amount of the large
      > cockpit seat watertight volume pushed below the waterline. In the
      > beam ends attitude the cockpit seat volume would be offset to the
      > wrong side of the beam ends centre of bouyancy which would mostly
      be
      > that of the cabin volume. This unwholsome coupling of weight up in
      > the air and more or less counteracting seat bouyancy linearly in
      > line with it (if not actually directly below it) could easily tip
      > the boat at least so far that water would gain entry via the hatch
      > and lead to the early reported flooding incidents that greatly
      > concerned many.
      >
      > If the cockpit seats were not water tight the Martha Jane perhaps
      > would just sit on her beam ends when knocked down... but then of
      > course the motor etc. would not be supported by their flotation
      > volume... Does anyone know if in the upgrade for the aft sponsons
      > the seats are able to have hinged lids for under seat storage
      access
      > because the flotation there is no longer necessary, and whether it
      > may be advantageous if they actually flood?
      >
      > The added sponsons act against the boat tipping past beam ends.
      The
      > addition of a 500lb steel plate design upgrade below the bottom
      > would also serve to act in this way. The trouble there is that
      > Martha Jane was designed to do away with fixed ballast to make for
      a
      > better trailer sailer than Black Skimmer - with the added 500lbs
      > steel ballast is there any advantage?
      >
      > Does anyone know if the original water ballast tanks are done away
      > with and their space is freed up for storage etc. when the steel
      > plate ballast option is installed?
      >
      > Graeme
      >
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