repairto kevlar yacht

Discussion in 'Fiberglass and Composite Boat Building' started by charleset, Mar 31, 2008.

  1. charleset
    Joined: Mar 2008
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    Location: hexham

    charleset New Member

    frames atatched to hull of yacht showing signs of stress cracks. Yacht is made from kevlar and polyester resin.
    once the cracks are ground out. do you replace the material with more kevlar woven glass sandwhich mix and polyester resin or epoxy?
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Who ever built your boat should be shot, for using a high modulus fabric with a low elongation resin. If you have the ability, run as fast as you can away from this yacht. If you're married to it, then the honeymoon is over and now you have to deal with her cold feet . . . Epoxy might help, but you'll still have lots of polyester to contend with as the years go by.
     
  3. the1much
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    the1much hippie dreams

    is the WHOLE thing kevlar,, or 1 layer of,,or that cheap stuff people call kevlar that has maybe 5 strands out of 100 of it? ( cause we all know,,even the BEST names have done all of em)
     
  4. Herman
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    Herman Senior Member

    In any case, when repairing, use epoxy resin. Grind out the damaged parts, then replace the ground out parts with new laminate. Be careful to taper the new laminate nicely onto the old, and do not create "hard spots".
     
  5. the1much
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    Location: maine

    the1much hippie dreams

    i think charlie left us,,,,soooo,,,,hows everyone doin?
    hehe ;)
     
  6. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    I might have pissed him off, but I could give him my ex-wife's number and they could talk about how easily this seems to come to me at times . . . (we all have skills of some sort)
     
  7. the1much
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    the1much hippie dreams

    well wheneva they see you and me post in the same thread,,,they otta KNOW 1 of us is gonna piss em off hehe ;)
     
  8. ratrace2
    Joined: Dec 2007
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    ratrace2 Senior Member

    Ya know guys, reading about all of this "rotten stringer repair"; Pars', "Who ever built your boat should be shot, for using a high modulus fabric with a low elongation resin" makes me wonder about an idea.
    Why not, or what would work, for fabric and resin if the stringers and "internal" structure of the boat was GRP/Frp and aluminium???
     
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    GRP structures are engineered, not "winged" though many have successfully done just that, but with the result being excessive weight, material and labor costs. Standard ortho polyester resins tend to be brittle, cracking under high load, instead of stretching and returning to it's original shape, when the load is released.

    Iso polyester resins are slightly better then ortho and successful use of high modulus fabrics can be employed, but usually not worth the increased costs for the small gain in strength.

    Vinylester resin have much better elongation properties then the polyesters, meaning use of modern, high modulus fabrics is advantageous. The resin will stretch along with the fibers and both will fail roughly at the same time or they'll return to their previous shape. This is the goal of matching the material qualities to gain an engineering advantage.

    Epoxy is better then any of the afore mentioned resins in every regard. So much so, that mat type fabrics aren't necessary in the laminate. For the most part, epoxy laminate hulls aren't necessary except in high end racers, where strong, light weight layups are required. This is where the exotic fabrics come into the engineering.

    My point is the use of a resin that will fail long before the fabric does, is a waste of some really expensive fabric and truly foolish engineering, not to mention construction.

    Ratrace2, I'm not sure I understand your question. Sure you can incorporate aluminum in stringers and other structural elements, but bonding with epoxy isn't as effective as welding, which is easier too. Do you have something specific in mind?
     

  10. ratrace2
    Joined: Dec 2007
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    ratrace2 Senior Member

    LL,
    Once again, thanks mate.(you are a walking boat encyclopedia)
    I never "wing" it. I usually try get a number of people to agree with me on an idea before I do anything; even then, I know what building codes are for, and I'm beginning to understand scantling rules, and agree with the theory and purpose of both. Industry standard are standards for a reason... .
    _____________.I think I almost have enough ,i.e. know enough, to present an idea to a real NA.____________
    How about a 37' to 40' cruiser, planing hull, "Jersery Vee" kind of hull. A nice sharp entry, Destroyer looking kind of keel (See Wally Wallypower 118, Ferretti 8080); very high free-board 6'8" to 8' at the bow straight to the transom; 14 ft at the beam. A Lurssen "Capri" styled Salon and flybridge. Hull painted deep blue like Kaptin-Jer's "West Wind." A single 6cyl diesel Cat with bow thrusters.....Low and Slow: Lingering about New York Harbor looking at the lights of Manhattan and cruising the Hudson..Cruising up to West Point, NY; tucking into a little cove somewhere for a good nights sleep.

    Yes I do have something--a couple of things--in mind, I just wanted to miss all the fun of replacing rotten wooden stringer. I was thinking that on "new" construction one could just use aluminium (what ever grade the engineer specifies) Or a combination of core material and aluminium to build up the stringers. It would be so much faster (from CAD template) to just weld up an aluminium skeleton and then glass it into the boat (shell) and just bold your salon and flybridge to the frame but still glass the seams for cosmetic and structural reasons; make the boat a cohesive unit (shell).
    Much like a house......just no wood to rot...No wood to distort with bolt compression.

    Yes, I do have something in mind, I just haven't, quite, been able to articulate it....hahahahahah. Getting "close", over the next couple of months I'll start working out the design in CAD/3D and let you have a look at it..
    _____________________________
    Responding to a different thread:
    OK, so if that guy had used Kevelar and Epoxy with his boat he would have been OK.....Because Polyester with kevelar is a waste of very expensive fabric, because the cheap polyester resin is going to fail way before the Kevelar fails; thus a waste of Labor....and fabric....
     
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