6.5 to 7.5 metre performance/cruise multihulls

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

  1. redreuben
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    redreuben redreuben

    Gary,
    Thinking aloud here, humps idea is awesome but separate points for reinforcement. With the central pivot, would that also incorporate the mast step ?
     
  2. hump101
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    hump101 Senior Member

    Losing the cabin could be a deal breaker in such a small boat, I hadn't realised you had one.
    The single beam will be supported at both gunnels, but the bending moment will only be resisted by the gunnels if the central bearing allows the beam to bend in the middle, which the described constructions didn't sound like they would, hence the beam and the boat would need to be strong enough to resist the resulting reaction force.
    I would build the split beams in the same manner as a single beam - a ply box with some carbon ud on upper and lower faces, plus around pivot points, which I'd use a block of timber between faces with a suitably sized bolt hole through. You can taper the inner portions of the beams so that when unfolded they look homogeneous.
    There is some redundancy in the split beam design, so do check your weights before committing to it.
     
  3. Gary Baigent
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    Gary Baigent Senior Member

    Yes, the gunwhales would need plenty of carbon, loads would be high there, especially when Sid650 lifts off and flies on uptip foils, eh Doug?
    But same would be necessary with single beam. Sid 850 has uni directional carbon towes running from gunwhales and around the double ring frame to the halfway stringers. After 18 months; no problems there.
    The cabin is very small on S850 and S650 would be similar size if with the single beam. I'll do some more sketches. Check out photograph of Sid's cabin? placed aft of the box section of main beam.
    The mast step? That is tricky on the scissor? setup. On my original single beam the central bearing with the mast step on top of it makes one single structure. Which pivots with the main beam. And I like that simplicity.
    Whatever I do, the gunwhales have to be beefed up, either to take locking pins or Hump's bearings.
    Maybe I should build two boats?
     

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  4. hump101
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    hump101 Senior Member

    The mast step could sit between the two beams, but then the boat would need reinforcing at this point, negating some of the benefits of the split beam. Not such an elegant solution, I agree.
     
  5. Marmoset
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    Marmoset Senior Member

    I still prefer the "kiss" method. I like the split beam idea a lot! I think on a bigger boat that was semi cruiser and would be taking on extra weight and nick knacks anyway, it'd be worth it. But to engineer yourself into a hole for something that just has to swing out the way for storage might not be prudent. In single mast and bearing setup it need zero strength when swung, it just needs to be strong when out. That should be do-able when it's all happening in a single location.


    Barry
     
  6. Marmoset
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    Marmoset Senior Member

    Just had a thought looking at that picture, how wide are you at the stays? What about all rigid till there with folding down or up outer sections? Like a plane on a carrier.


    Barry
     
  7. Gary Baigent
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    Gary Baigent Senior Member

    Barry, I'm leaning towards the original single beam because although I really like the brilliance of Hump's split beam design, I see problems too.
    On Sid 8.5 there are two diagonal water stays (hollow, airfoil shaped, carbon reinforced) running from below the shroud connection points (approximately 4 metre total spread on main beam) to the double ring frame inside main hull. More carbon at all the junctions.
    Because Sid 650 has a proportionately wider hull and greater flare than the 8.5, was hoping that the wider base might allow me to NOT have water strut/stays ... but also know that you breath easier when the gusts come through with the struts because the rig loads are carried around the triangular stayed setup, keeping the platform from flexing and in one piece. Your suggestion of outer wing folding/turning? - I see too much engineering required. Je suis une garcon rural.
    If no water stays, there will have to be heavy carbon laminations to stiffen/strengthen platform. Prefer the KISS principle of the stiff water stays.
    So the two Sids will have the Jan Gougeon approach as seen in this photograph of his conventional two beam 25 foot design - but only one strut per side. Notice how fine the two beam thickness is on his design; this allowed because of the water strut stays
     

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  8. Marmoset
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    Marmoset Senior Member

    Your dead right actually, it's avoiding a tarpit by jumping into quicksand, just more doses of making it difficult for no good reason.



    Barry
     
  9. Gary Baigent
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    Gary Baigent Senior Member

    Haven't done much on Sid650; turned frame over, added a few more sticks and forestay bulkhead - but have built main daggerboard and T rudder. However haven't been completely slack because I'm giving the Cox's Bay Skimmer away to a Waiheke sailing enthusiast - but before we sail the "sketch" rigged dinghy to the island, have had to lower the wing masts and fix some splits in the bendy ply skin. So when the wind changes to give us a reach instead of a long beat to Putiki Bay, will say bye bye to the skimmer. I have too many boats ... and building another; must be bonkers.
     

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  10. Marmoset
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    Marmoset Senior Member

    I swear that looks more aircraft then boat! Haha


    Barry
     
  11. basil
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    basil Senior Member

    Gary,

    If you ever think again that you have too many boats; I'd be very happy to become an adoptive father and give one of your children a beautiful life on the Gold Coast in sunny Queensland Australia.

    Tony
     
  12. basil
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    basil Senior Member

    And I'm not talking about being free either.
     
  13. Gary Baigent
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    Gary Baigent Senior Member

    Bit of an expensive transport problem getting the black skimmer to your place though, Tony. On the other hand, could sail it over ... 18 foot dinghy across the Tasman?
     
  14. Gary Baigent
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    Gary Baigent Senior Member

    Here's dagger board and T rudder temporarily placed in position.
    Since I readied and made repairs to the Cox's Skimmer and sailed with Jacques to Waiheke (10 knots top speed, took us 3 hours 12 to get there from Cox's - good to get rid of the mono) - can now devote more time to the 6.5m. Next job is to bend/glue the thin ply skin on.
     

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  15. Doug Lord
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    Doug Lord Flight Ready

    foils

    Geez, Gary-don't forget the foil on the daggerboard.......
    Going to be a great looking boat!
     
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