Your advice please......

Discussion in 'Fiberglass and Composite Boat Building' started by 40Skater, Aug 6, 2008.

  1. 40Skater
    Joined: Aug 2008
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Arizona

    40Skater New Member

    This is a first class forum! Everyone here has great advice.:)

    Here is my question....

    I have a 40' catamaran. It is made up of balsa, S2 glass and Kevlar. Right behind the backseat were the cockpit ends I have some pretty good cracks on both corners. I assume this is a pretty big stress point. Last year I had a guy come out and fix them. Well, they were back after the first trip. I have ground out both corners and found that he just added some epoxy and called it good.
    I have ground into the balsa on both sides to get into fresh material. There is no longer a 90 degree were the wall hits the deck because of my grinding.
    A. Do I cut balsa to fill in the void so that it is back to the original shape and then glass?
    B. Do I just start glassing and remake the corner with some filler?
    C. Do I start with the S glass first and then Kevlar, or Kevlar then S glass??

    Any help would be great. Thanks.
     
  2. tinhorn
    Joined: Jan 2008
    Posts: 575
    Likes: 20, Points: 18, Legacy Rep: 310
    Location: Massachusetts South Shore.

    tinhorn Senior Member

    Here's what I suggest - make sure you replace the 'glass you ground away with as much or more as you removed. Then 'glass in a brace of sorts to reinforce the joint. Rip some straight 2x2s into triangles, bond them into place, then cover with 'glass as thick as the first layers you applied. The strength will be in the 'glass, not the wood so much. You use the wood (or foam or wadded-up paper towels or whatever you choose) to create the shape.

    Make sure you're laminating to pure, raw, ground-off fiberglass. Anywhere you bond to unprepared 'glass is where your patch WILL begin to delaminate. And forget the Kevlar. It's a pain to work with (sometimes very difficult to wet out properly) and for this project, its qualities aren't really essential.
     
  3. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Tinhorn has most of it. I'd skip the wood altogether and just use a pure laminate (fabric and goo). If the cracks reappeared quickly, clearly this is a highly loaded area, as would be in the location described.

    Feather the area well back, with a gradual, sloping taper (10 times the thickness of the laminate or better) into the 'glass. Don't even try to bond to the gel coat, you're just going to have the cracks come back. After you've moved the damaged area back, closely examine the cracks, checking to see if they go through the outer laminate. If they do, it's possible you have other issues, such as delamination, core deformation,, sheering, etc., which needs to be addressed differently. If the cracks don't go through the laminate, grind them out or nearly so.

    Since you're into the core, you need to place something back in there. Wood is an option, but I'd use fabric. Wet it out, bulk it up and get it relatively close to the shape you want, say within a 1/16 of an inch shy of flush with the surface. Use layers of 45/45 biax and cover this with 1708 with the mat side facing up (prevents print through and finishes easier) to do the bulking out (you could use all 1708 if you want).

    Now you've got a well reinforced area, which spreads the loads over a larger area, has sufficent bonding plane and high modulus fabric, which takes best advantage of epoxy's physical properties.

    Yep, we offer great advise. My advisory tip for the day is ". . . don't take a laxative and a sleeping pill on the same night . . ."

    Apply a fairing filler over the area and block her smooth, then paint to suit.

    I agree with Tinhorn, in that on such a small area, the use of an exotic fabric (Kevlar) isn't warranted. Sure the area will be a few ounces heavier then before, but it also will not crack like before either.
     
  4. 40Skater
    Joined: Aug 2008
    Posts: 3
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    Location: Arizona

    40Skater New Member

    Thanks for the help guys!!! :D
     
  5. the1much
    Joined: Jul 2007
    Posts: 3,897
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    Location: maine

    the1much hippie dreams

    mannnnnnn,,,, you guys beat me,,,,,i was gonna say,, just crumple up some newspaper and shove it in the hole,, and glass over it ,,hehe :D;)
    i just want ta add,,,,that kevlar in a boat is 1 of the biggest SCAMS in the boating industry,,,,,usually its regular glass with a FEW threads of kevlar,,,,and even the ones that use kevlar "sheets" usually just use 1 THIN layer,,,,which even though it SOUNDS like a cool thing,,,it doesnt do ANYTHING for ya,,,,,,the only way to make kevlar worth what they charge ya,, is to make ya boat out of ALL kevlar,,,,,,which in my head is just stooooooopid,,,,hehe ;)
     

  6. 40Skater
    Joined: Aug 2008
    Posts: 3
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Arizona

    40Skater New Member

    For what they charge for a 40' Skater you would think it would be solid Kevlar....:D
     
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