6.5 to 7.5 metre performance/cruise multihulls

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

  1. Gary Baigent
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    Gary Baigent Senior Member

    LOL Hielan - but, but a huge bearing like so would weaken the main beam, would it not? I'm kind of concerned about main beam strength. Needs to be one integral unit (because it will be 7 metres long and there are loads at that mid section).
    Here's how I built Sid's 8 metre beam, with a box for central strength and stiffness; would not want to cut into said box.
    In fact, imo, the bearing should be no larger than the box and be heavily reinforced in that area.
    You can see that, although I delude myself as a flexible thinker, can be quite rigid and dogmatic too. Cheers.
     

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  2. Doug Lord
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    Doug Lord Flight Ready

    Ok Gary, it's time now: you've just got to try UptiP foils on your amas. Just think of it: automatic altitude control with no moving parts! You can tweak the foil to work just the way you want it to with minimum design work to start with...... You could have the ama fly one foot above the water no matter what the main hull does -in other wors it can maintain the design altitude most of the time regardless of speed and load.
    PS- you could do like Gitana is doing-one uptip foil on the port ama......
     
  3. redreuben
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    redreuben redreuben

    Gary thats why the waveform shape just horizontal effort should be enough to make it ride up to the next location. And I agree, size of the box would be enough, hull width is heavy overkill.

    Anyway, sounds like you have a plan.
     
  4. HASYB
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    HASYB Senior Member

    Good heavens Gary,
    The bearing should firm the whole construction up not weaken it.
    You sound like you've taken a bath in concrete my friend.
    I'm sure a high-priest of tortured ply, ring frames, boxes and wings should be able to get his head around such fussiness while floating.
    Perhaps float some more, water preferred, and think of a front beam and an aft beam for the wing beam with an integrated tapered bearing with both, font and aft, beams tapering into the end of the wing beam.
    For the main hull same story, it should be part of the construction and reinforce the swiveling spot.
    When you wedge the bearing together it will have a nice huge surface where the total structure can carry and divide the forces & momentums.
    But then again It's your party.

    So hey, float some more, constructive and flexible and please don't wrinkle, lol

    Cheers
     
  5. Gary Baigent
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    Gary Baigent Senior Member

    Apologies Hielan for my er, stupidity but ... if I'm reading you correctly - and maybe lost in transllation a bit, but I want an airfoil shaped beam and I think you're saying two I beams spread apart with a large bearing connecting the two, like attaching the fore and aft I beams together. No problem but ... that is a very large chord beam even without an airfoil shape, which if fitted, will make it even larger. I'm all for wing shapes and so on but this setup will be too large for the 6.5 m boat.
    You need to draw a picture for this simple country boy.
     
  6. Gary Baigent
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    Gary Baigent Senior Member

    You're right Doug, and by the way, the new foils on Groucho have an UPTIP! See, all capitals, not this funny 50/50 font stuff.
    With Sid 650 I wanted absolute simplicity so was thinking of the Holtom triangular foils/floats - but changed mind and will go with the larger original Sid floats plus the type foils you advocate. But a long way to go before I get to that area of the boat. Have laid up main dagger and T rudder. Incidentally, I crank the inverted T section up, purely for practical reasons when sitting on the hard, but you could say the rudder foil too, is uptip.
     
  7. HASYB
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    HASYB Senior Member

    Au contraire mon ami, the apologies are totally on me since I so rudely interfere with your superior boatbuilding ideas.
    LIT, I guess so or perhaps not at all because indeed what I meant was a wide, width of main hull, wing shaped beam in the middle tapered to narrower wing beam end.
    With in the middle a largest possible bearing to take accountable care of the applied loads with light & strong construction
    You would only need to construct something of a front beam and aft beam structure inside the closed wing to take the loads. The beam like structures, in front and aft of the bearing, wouldn't need to be full length of the swiveling wing shaped beam.
    What I envisioned was closed wing with a structural integrated, as wide as possible bearing.
    You're maybe right that it's probably to big for your Bad Insect though cause I also thought if you respectfully opened up the bearing a bit you could use the place to sleep.

    OK? Savvy?
     
  8. Gary Baigent
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    Gary Baigent Senior Member

    Okay. Je comprend. But have to rudely say, mon ami, that your wide to tapering beam is way too large. But it does allow one crew to sleep in the bearing. Which is outside the box (actually inside) thinking.
    So the bearing/turrent/cabin is the strength of the mid section of the beam. I don't think it would be. You would have to run webs and carbon reinforcing over and under the turrent/bearing - and then you wouldn't have enough room to sleep. And it would be heavy.
    Actually when building Sid I thought a bunk could fit crosswise in the flared hull area ... but in real world, it was far too cramped; you would be curled up in foetal position all night long, couldn't roll over.
     
  9. HASYB
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    HASYB Senior Member

    So what cord and width/hight of the winged beam you expect to build?
    Sorry again for the consternation.
     
  10. hump101
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    hump101 Senior Member

    Gary, just thinking about your pivoting beam, what about splitting the beam in two, so that you resist the bending moment across the full width of the main hull, not just half, and avoid a big pivot bearing in the middle of the cabin?

    You'd only need two strong points, one on each gunnel, carrying the one beams pivot and the other beams clamp, so a potentially lighter overall structure. The pivot needs to cope with the folded bending moment, but if the beam rests along the gunnel as it pivots this BM need not be excessively high.

    You could also just fold one side coming alongside, if this would be of use. The geometry also allows for a smaller overall beam, and slightly longer floats within the trailing width.
     

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  11. Gary Baigent
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    Gary Baigent Senior Member

    That split beam is very clever, Hump (this coming from an amateur enthusiast, so probably doesn't mean very much).
    It means building three bearings though, and the cantilever loads on the two outer ones would require some special reinforcing. Giving it more thought time. Cheers.
     
  12. HASYB
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    HASYB Senior Member

  13. Gary Baigent
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    Gary Baigent Senior Member

    I knew a little about Jo's Toy (was it at Golden Oldies with the other proas?) and can see why you like the large canopy-type cabins (large bearing-like shape?) of a few of Kergomard's designs, (he is definitely a radical thinker) - but notably the circular beam carrying the two wing rigs on his catamaran. But as I see it, although the rigs can turn on the curved track for differing sailing points, the rail is supported to fixed curved beams which echo the shape of the track; meaning the two connecting beams are of an unusual plan form curved shape. But the circular beam shape does not turn, just the traveller mast bases on the track. Whereas your suggestion for the 6.5 is that the the circular beam is a very large bearing allowing the beam to turn 90 degrees ... and that, to me, would be difficult to build and implement in terms of weight and beam strength.
     
  14. hump101
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    hump101 Senior Member

    Just a couple of bearings, one for each beam, unless you want to pivot the floats, but these bearings can be as simple as a loose bolt, as it's not got to carry load and pivot at the same time. The pivots are adjacent to the clamps, so that location has to be strong in any case to resist the RM uplift force when sailing. The downforce at the bearings will be half that for a central bearing.
     

  15. Gary Baigent
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    Gary Baigent Senior Member

    So I roughly sketched a single beam version of your excellent suggestion, Hump, with required pivoting and reinforced bearing/pin positions.
    The only disadvantage I can see is that I will lose my small cabin. Which is not a problem; below the beams will be a flush deck - so I'll put a flush hatch there instead.
    The spread apart two point pivoting/locking positions would give good cantilever support. I like that. But the single beam also does the same job (because the two outer pins also give a wide spread cantilevering position). I have to think about how I would build the double (scissoring?) beams.
     

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