6.5 to 7.5 metre performance/cruise multihulls

Discussion in 'Multihulls' started by Gary Baigent, Feb 27, 2015.

  1. upchurchmr
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    upchurchmr Senior Member

    If I remember the D leading edge was an MIT design for a sailplane - at least the first time I heard about it.
     
  2. Gary Baigent
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    Gary Baigent Senior Member

    You can go back to late 19th and early 20th Century aircraft/glider wings, same principle, airfoil shaped leading edge followed by doped canvas over frames and stringers. Only difference to a D shaped leading edge double sail rig is that the following assembly has to be flexible. But not as flexible as a conventional mast/wing mast/single sail rig because the double rig and D shaped leading edge does not have to rotate as much ... because the windward sail fairs the wind flow better without the stagnant bubble immediately aft of the mast. See photograph of Groucho's mast setup for light air windward sailing. That is quite a lot of rotation - and the more rotation (for reaching/running) the larger the draggy to windward bubble.
    Frog's rig bearing is set at the very front, not a third or so of the way aft as on my other masts. Meaning it doesn't have to rotate beyond, say, 40 degrees - and probably less. Will find out soon enough.
    Laying/gluing D frames and stringers out in my shed right now.
     

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  3. Gary Baigent
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    Gary Baigent Senior Member

    Have been ordered to shift THAT boat out of the backyard. So cruel, so selfish - meaning her, not me. I mean the only time "she who must be obeyed" goes down the back section is to pick a few herbs from MY garden. Life is hell.
    Anyway the platform has been finished and it is time to move. The D shaped leading edge mast is ready for skinning and the design of which is undergoing sophisticated thought and mental fine tuning - how can we, Bill Barry and I, fail - and the weather has improved dramatically here too. The shining cuckoos have arrived very early from the central Pacific. Maybe that is telling us something?
    So here is the Frog parked on its side in the narrow confines between house and fence (some radical tree pruning and considerable time was required to achieve this success); the beam is out front ready to be loaded and both are to be trailered to the sparkling Waitemata, bolted together and placed on a mooring while the radical mast is finished.
     

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  4. redreuben
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    redreuben redreuben

    Gary, I assume the leading edge of the "D" shaped mast is the same shape as you wing masts just truncated ?
     
  5. Gary Baigent
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    Gary Baigent Senior Member

    Yes, just chopped off at the central I beam position and the two tracks attached each side. I've tapered the above hounds mast areas. athwartships and fore and aft ... so I'll have to use two halyards for the main (because of the narrowing of the tracks there). Bill is going for a single halyard on his design with, I presume, a strut across to the sail peaks and therefore no taper to the mast.
     
  6. rberrey
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    rberrey Senior Member

    Kill the herbs Gary , problem solved .
     
  7. redreuben
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    redreuben redreuben

    Gary, another question, would I be right in thinking the sails for the "D" mast would be pretty much flat panels ? The shape would all be derived from mast rotation yes ? Apart from battens ? That would put them in the realm of DIY ?
     
  8. luff tension
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    luff tension Junior Member

    Yes possibly, but not many DIY'ers have reasonable access and/or stock of good fabrics and other sailmaking fabric necessities - heavy machinery capable of sewing through multiple layers of webbings, eyelet die-sets, a 3 step machine for the seam construction details so the sails stay together, a 9m + long space to deal with luff rounds etc, fairing battens etc etc, oh, and the CAD system to actually design the sails. Then we need to add the actual "seat of the pants" skills involved.
    Perhaps its not a DIY thing at this size after all.
     
  9. Gary Baigent
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    Gary Baigent Senior Member

    You probably are right, Luff tension, but foolishly I/we still forge ahead.
    The lightweight sail material that Bill has in stock is very exotic and mostly transparent looking stuff, sewing, he says, is no problem; and he's the expert so I mostly keep my mouth closed and just listen.
    Tomorrow I skin the D section, have completed the I beam area and after that will go over to North Shore to see what BB is up to; will take some photographs of the material and of the sail design sketches. The double sail will be two singles cut flat, hoisted together and attached at batten ends. According to Bill the leading D section will only need to rotate around 9-10 degrees. I knew it would be way less than "conventional" wing mast, single main but that is a very small figure.
    Fools go where angels fear to tread.
     
  10. basil
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    basil Senior Member

    G'day Guys,

    If anyones interested the latest Google Earth shows mast lying at either the bow/stern of Groucho.

    Tony
     
  11. santacruz58
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    santacruz58 Senior Member

    I can never find them on google maps. Dont know Auckland well enough to know where to look. What bay or inlet would I look in?
    nelson
     
  12. Gary Baigent
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    Gary Baigent Senior Member

    Happened some months ago in horrible wind and seas. The bay is Cox's west of the bridge on south side of harbour.
    Poor Groucho and mast haven't been repaired; too busy with the Frog. Jacques says cut the old boat up and put it in a bin. But I'll get round to fixing it later. If the double luff rig on Frog works, might change to similar setup on the Grouch.
    Just checked Google Earth, that is not Groucho in Cox's Bay but the Power of 2, a Tennant 52 foot catamaran (see photograph, which is for sale for 200 grand by the way) - and I don't know why the mast appears to be down because that didn't occur; must be something wrong with Google perspective. Also it is not the latest Google version but an image that is maybe 4 years old.
     

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  13. basil
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    basil Senior Member

    My mistake - the image is an old one. Cut it up - you have to be kidding.

    Tony
     
  14. Gary Baigent
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    Gary Baigent Senior Member

    Shifted Frog with help from Eric Eason. Frog appears to overload the poor car but actually the amphibian's main hull weighs only 56kgs; so the two of us just lifted it onto the racks. 4th photograph of 8.8 metre D mast.
     

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    Last edited: Sep 7, 2016

  15. Gary Baigent
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    Gary Baigent Senior Member

    Frog afloat in shallow water; hope to have the D mast finished this week.
     

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