laminating beams and bulkheads with cloth

Discussion in 'Fiberglass and Composite Boat Building' started by robwilk37, Nov 10, 2012.

  1. robwilk37
    Joined: Nov 2010
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    robwilk37 Senior Member

    is there any benefit when laminating wood to lay carbon or biax cloth in the seam of epoxy before clamping? im thinking specifically of deck/cabintop beams. or between plywood layers for bulkheads? or is this just a waste of resin and cloth?
     
  2. TeddyDiver
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    TeddyDiver Gollywobbler

    Biax not much, some uni might help thou if calculated correctly. Note that biax is a form of cloth (biaxial ie layers of fibers with differing orientation) nothing to do with the material which can be glass, carbon or whatever choosen. Uni ie unidirectional has all it's fibers oriented in one direction only.
    BR Teddy
     
  3. PAR
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    PAR Yacht Designer/Builder

    It would depend on loads, the size of the veneers in the laminate stack, etc., but generally, no, unless you are using much thinner veneers than necessary, in order to take advantage of high modulus fabrics.

    A more specific application description (yours) is necessary, to really tell what's going on, but generally, nope.
     
  4. robwilk37
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    robwilk37 Senior Member

    it was just a thought. ive got a bunch of epoxy and a bunch of 1708 that id like to put to good use on this rebuild. i bumped the cabin top up 4 inches for head room while below. planning to laminate 2x2 crowned deck beams from some beautiful old growth doug fir (dead straight vertical grain with rings so tight you cant count them). then overlay 2 layers of 1/4" marine doug fir ply and top with layers of biax/epoxy tied into the side deck glass. beams on 24" centers. this is substantially more than what i had before this particular mod but that doesnt mean its adequate. opinions? how many layers of cloth? cabin top sides are 3/4" marine doug fir screwed and epoxied to doug fir carlines. i can also laminate from quarter-sawn white oak if that would be a better material...although a bit heavier and not a natural friend to epoxy.

    also replacing the original bulkheads (rotten 3/4" cdx) with 2 layers of 1/2" marine doug fir ply laminated together with epoxy. so was wondering if cloth in between contributed anything or not.

    like i said, ive already got the material. i dont want to piss it away but if itll contribute in a positive way then im open to ideas...

    as always, thanks in advance.
     
  5. michael pierzga
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    michael pierzga Senior Member

    Sometimes fibers are added to a wood laminatinion to control springback or to keep the wood laminations from splitting.

    its easier to laminate wood only to the desired strength , then trim the springback off with a hand plane .
     
  6. PAR
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    PAR Yacht Designer/Builder

    1708 is just a waste of resin with epoxy laminates. Save the 1708 for polyester or vinylester layups. Spring back (I don't know what Michael is talking about) can be controlled with the laminate stack. The more layers, the less spring back. On a 2" tall laminate stack, it's tempting to just use four 1/2" thick layers, but spring back will be about 10% of the curve diameter. Increasing to 6 layers (a short 3/8") will half this and 8 (1/4" layers) will all but eliminate any spring back, once the beams are removed from the jig.

    Again no, the fabric between the layers isn't going to do much, except add to the complexity of the job. 2 layers of 1/4" plywood over the beams will make a nice, stout roof. Stagger the seams and do half a Payson butt joint on the exposed faces, for a smooth transition.

    As to exterior sheathings, well you can do whatever you like, but for the most part it's just abrasion resistance. So, if you expect dance parties on the roof, you'll want some Xynole or a heavy sheathing (24 ounces or better), but if you're like most and will contain dancing to the cockpit, a light 4 to 12 ounce sheathing all that's necessary.
     
  7. robwilk37
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    robwilk37 Senior Member

    thanks all...

    par, ive read in other posts your comments about 1708 being a waste of resin when using epoxy and im wondering why that is? and why it would be different for the esters? is it just wasteful of an expensive resin or does the over saturated mat actually compromise the strength of the lamination?
     
  8. PAR
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    PAR Yacht Designer/Builder

    Epoxy resin doesn't need, nor is it desirable to use mat. The mat in 1708 is a bulking agent, necessary in the lower modulus resins, such as polyester and vinylester. These resin systems need the mat for stiffness, but epoxy doesn't and if used, just makes the laminate resin rich, which is weak and wasteful. Simply put, a 1708 laminate with epoxy will use 2 to 3 times as much resin as a straight 17 ounce fabric, meaning the laminate is quite high in resin and low in 'glass, which isn't what you want. An ideal laminate has as high a 'glass to resin ratio as practical, assuming full wetout. This places a high percentage of fibers under load, instead of resin, which is the goal with 'glass laminates
     
  9. robwilk37
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    robwilk37 Senior Member

    clear as crystal...thanks so much.
     
  10. Steve W
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    Steve W Senior Member

    What Par said is right on, i would favor more laminates, 1/4" or 3/8" and save the glass for another project. What is the boat? 1" bulkheads sounds pretty heavy, even the original 3/4" is pretty stout.

    Steve.
     
  11. robwilk37
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    robwilk37 Senior Member

    yorktown 39. ive got a full lift of 1/2" MDF and want to use it and two pieces of half are just easier to muscle up the ladder and into position. im staggering the seems by a foot or more with a half payson on the exposed side. probably overkill...

    and MDF stands for 'marine doug fir' (plywood). thickend epoxy between the panels and 3 coats neat everywhere else. got a deal on 110 gals of epoxy and not afraid to use it. 17oz biax tabbing 1 foot wide, 5 layers, all seams staggered... deffinately overkill.

    the boat will cruise so some piece of mind there.
     
  12. Steve W
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    Steve W Senior Member

    You had me worried a bit when you said MDF, im glad its not medium density fiberboard as used in kitchens. I would think that one layer of 1/2" scarfed or even splined together would be plenty strong enough for any bulkheads in a boat of that size. Overkill is not a good approach in boatbuilding, even with a heavy displacement boat, every pound of structure you add that is not needed is a pound of cruising payload lost.

    Steve.
     
  13. tunnels

    tunnels Previous Member

    What you wanting to do is placing the composite completely inthe wrong place between and clamping why would you want to do it that way ?? what about top and bottom of the beam and epoxy with unidirectional carbon two layers top and 4 to 5 layers bottom and a light weight (400gram or 600gram )double bias to hold it all together . bend is the top and bottom surfaces wanting to fight against each other !! :rolleyes::):p;)
     
  14. Steve W
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    Steve W Senior Member

    If the vg doug fir you are using for the beams is reclaimed from old beams there actually may be some merit to including some fiber in the joints as doug fir gets very brittle with age. I have personal experience with this as i used to rent a shop from a friend whose business is making high value architectural beams etc out of old reclaimed doug fir, southern yellow pine beams and redwood wine vats, its a big operation, some of the vg fir is magnificent but when cut into stringers,fairing battens etc it simply does not bend like the more recently milled stuff i have used for gunwales, carlins, deckbeams etc. The yellow pine does not seem to get brittle like the fir. If what you have is "new" old growth doug fir i definatly would not use glass in the gluelines, just use 1/4" veneers. I have in actual fact used fiber in the gluelines on one project, back in 1980 i built a 7ft diameter steering wheel for the first composite IOR maxi raceboat "Kialoa" at Kiwi boats in Florida. It was laminated out of very thin white ash veneers with carbon tows in every glueline,there really was no great reason to do so other than the appearance of high tech (there were a lot of things we did on that boat that could have been done lighter with more traditional methods but then they wouldnt be cutting edge)

    Steve.
     

  15. michael pierzga
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    michael pierzga Senior Member

    I'm attempting to rejuvenate a 20 year old carbon, ash , wheel right now.

    Waite till the owner sees the bill !!!!!!!!!!!!!!!!!!!!
     
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