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

    I stretch a tape and measure off the sections and paint metre marks on the floor; then while I erect my thin and bendy sticks, mes yeux tells me if I'm going wonky. You have to use said yeux when you start tensioning the ply onto the framework anyway because the material is under load ... and in my opinion, can't be done any other way. Well you could use many numbers of heavy stringers and frames on a strongback - but then the ply bends to its own set of rules ... so why not let it take its natural curves.
    I'm an arty farty sort of bloke and trust my eyes to tell me if shapes and forms are incorrect. I do spend a lot of time looking at the boat from many angles, changing this and that while I work. Which is okay and kind of fun.
    Bent ply or bent any other material like glass or carbon sheet, is different to flat ply and chines. But having said that, the same approach could be used in the latter too. But it is not the done thing, as Jim Young would say of his early pioneering boatbuilding methods.
    There is a marvelous book by Howard Chapelle titled, "The Bark Canoes and Skin Boats of North America" where there are images, drawings and photographs of the indigenous people building their beautiful canoes under trees in very much the same manner, using their eyes and measuring sticks.
     
  2. patzefran
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    patzefran patzefran

    Thanks, Gary, You build like a sculpteur. I have not this skill, I am only a retired engineer ! I have still not completely understood how you transfer the plan's sections to your bendy sticks ! do you measure (or compute !) the stick's length on your plan then mark the sections locations on them ? It seems the keel stick is supported only on three points, as well as the side ones. I agree, ply bend naturally and cant be much strained. It is difficult to understand how a such bendy wobling framework will support ply. I wait for the next pictures of the process !
     
  3. Gary Baigent
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    Gary Baigent Senior Member

    Patzefran, if you go to my "alternative to marvelous Buccaneer 24" multihulls thead here at boatdesign.net, you'll see all the build process of Sid. Warning: there are a large number of pages but you can just check out the photographs. Sid was built in the same way as the 6.5m will be put together. Oh yes, I don't rigidly adhere to the plan. That is just a pretty picture. Sorry. Because I change my mind as I go along.
    I'll be turning the 6.5 skeleton over in a couple of days and will align, pack and attach it to the floor, then begin the skinning process. I do two scarfed sheets both sides at the same time, so there is equal and balancing pressure, no twist as you bend the sheets down together to the gunwhales.
    And as my old mate Don Gifford says, I built with sticks and string, and that is true because I do use numbers of drawstrings through drilled holes to bend the ply together equally.
     
  4. patzefran
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    patzefran patzefran

    Thanks, Gary
    I looked at Sid building. Impressive set of photos. Have you any photos of the skining step ?
    To stapple ply on the keel stringer when skinning you need access under the keel ?
    I have some 3.10 x 1.5 m 3mm okoumé plywood. Next build I will try your method for new outriggers. I buit my 20' tremolino outriggers using the Tornado method, they were much lighter tha Nacra 5.8 hulls, but had some flaws along the keel.
     
  5. Gary Baigent
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    Gary Baigent Senior Member

    I've turned Sid 650 over so will take some photographs while skinning.
    You don't need to get inside the framework to staple/glue the ply to the keelson, you do it from outside - and only crawl inside later to cove/clean up the glue lines around the frames, keelson and stringer edges.
    Actually I'm going to build the 6.5 a little differently than the 8.5 - meaning to wrap a single sheet so that the keel timber is at the halfway bent position, like bend it over the frame, in simple English. Because the 650 has a wider, U shaped hull in cross section near waterline. Sid is more ogival, soft V.
    Whereas before I stapled/glued the two long ends to keelson, waited or heated it to cure, epoxy coated the inside, then bent each side down. Hard to explain. Will do photographs.
    .
     
  6. warwick
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    warwick Senior Member

    I will be looking forward to the photos as well Gary.
     
  7. Gary Baigent
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    Gary Baigent Senior Member

    Have been slack - but a small progress, after turning the skeleton over.
     

    Attached Files:

  8. oldsailor7
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    oldsailor7 Senior Member

    Gary. Love that shape, and you are obviously a whiz with ply forming. :D
     
  9. Tom.151
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    Tom.151 Senior Member

    Gary,
    About the trailer part... if you can consider transferring some of the functions for assembly/rotation to the trailer's elements then that (could) reduce the complexity of the boat.
    Attached is a rough idea for being able to lift and rotate the beam assembly 90 degrees by supporting a (temporary) bridge/beam that suspends a lifting tackle over the boat's crossbeam assy.

    The position of the support posts in opposing quadrants allows a full 90 degs rotation.

    Something like this could eliminate the need for "bearings" (or bearing surfaces at least) from being built into the hull/beam interface - and to allow a wider choice of planform shapes (or locations) for the interface joint.

    Dunno if it really applies to what you have in mind at this point, but this idea has been floating around in the back of my head since you first mentioned the concept of rotating the beam for trailering - which I though was a brilliant solution to the age old "folding trimaran" problem - just by tranforming it into a different plane.

    Love what you've done, and what you're doing here.

    Cheers,
    TomH
     

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  10. Gary Baigent
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    Gary Baigent Senior Member

    Yes, yes Tom, thanks, good thinking.
    However, ha, ha, I still think pivoting on a conventional tube bearing is the simplest solution, no beam lifting apparatus required, just pull the pins/bolts/release cleats whatever - and swing 'er round. This from the most recent intensive bath contemplation think tank.
    The square or octagonal bearing is also a good one - but you still have to lift the beam and then drop it into position. I want to avoid that if possible. Locking on the flat bearing areas has advantages but will still require spread out locking positions on the flared hull areas.
    However, have an open mind, always ready to change like a chameleon changes colour.
     
  11. Marmoset
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    Marmoset Senior Member

    Over here as not to clog buccaneer thread. The reason I thought decagon is that it allows registration points needed. A square or pentagon say, would want full 90 degrees leaving beams in boat, where as decagon allows a sweep to touch boat but not interfere. It's an easy shape to hot as well for bearing and receiver and tapped down middle just screw a ball in to hold it there. No clue how, but I even had the though of some kinda spring making receiver pop up as it's unscrewed eliminating need to lift and turn, but that might make things too complex? Another though is have a capture ring on washer for ball and it lifts shape off as it's turned. You could fab yourself up a long ply/glassed wrench to make it easy to turn.


    Barry
     
  12. basil
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    basil Senior Member

  13. HASYB
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    HASYB Senior Member

    My 2 cents for this work of art.
    I've been mulling about the swiveling beam since you started the "alternative to marvelous buccaneer" thread over in numerous meandering mind musings myself and came up with 2 pretty big, not wider than road legal, tapered ply rings or even closed or worked open tubs being able to rotate within each other.
    One ring getting its strength and give strength from integration with the centre hull and the other from the swiveling beam.
    It would be fairly easy to construct, easy to lock or unlock when pressed or released as well distribute and integrate forces over a pretty large area's.
    In some musings it even became a nice centre hulled, easy to cover for sleeping or not when the weather is good, cockpit.


    Cheers,

    Hielan
     
  14. Gary Baigent
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    Gary Baigent Senior Member

    Thanks Barry, Tony and Hielan. So Glen Roberts easily beat me to it. Great stuff. 26 x 31 feet, T foils, 15 year project so Glen was way ahead. Very neat small floats btw.
    I momentarily thought of going to the angled Holtom foiler type float/foils ... and then doing a Doug Lord, putting a T foil on the main hull dagger ... but then I can't get it out to allow swivelling the main beam; unless dagger foil removed or fitted from underneath, which is clumsy. You should see me refitting the T rudder to Groucho: deep water, moving boat, rudder wants to float, push down with foot, try and align with slot, treading water rapidly - but eventually I succeed. So no, not the answer, sorry Doug. So that means small floats a la Sid, and J or L type foils, with uptips of course? Note correct spelling.
    If I'm reading you correctly, H, I'm considering something similar, a home made carbon male bearing about hand plate diameter, slotted into female bearing with webs spreading out to distribute loads.
    Btw team? - a picture/drawing explains more than words.
     

  15. HASYB
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    HASYB Senior Member

    Think of 2 taper buckets, but way bigger, with or without bottom, easy turning when not compressed and locking and leveling when pressed together.
    In theory you don't even need the centre, if i read your idea correct, as it also don't matter if you turn the bucket forms 180 degrees if that can clarify the picture somewhat.
     
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