Stringer to Transom and Hairline Hull Crack Repair

Discussion in 'Fiberglass and Composite Boat Building' started by E350, Jun 22, 2019.

  1. E350
    Joined: Sep 2015
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    Location: Sacramento River Delta, CA

    E350 Junior Member

    Honey do work. As a 2-cycle standup jet skier, I am embarrassed to say that before I met my wife, a jet skier ran into the stern of her ski boat. It looks like the repair was insufficient because there is a hairline crack in the bottom of the hull under the port exhaust tube and the stringer to transom joint has a gap and the glasswork over the stringer leaked. I have ground down mostly to blond solid wood but I will let it dry some more in the Sun to make sure. Then I plan to cut up some cut strand mat and make a polyester resin paste and stick that stuff into the crack and cover with one or two layers of mat and then a layer of S-glass and then roll on some gel coat with wax. Team: Any other suggestions?
    DSC04569.JPG DSC04572.JPG DSC04566.JPG DSC04562.JPG
     
  2. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Good news; the transom core doesn't appear to have any rot.

    Less good news; you have more grinding to do. All of the gelcoat needs to be removed for 6 inches away from the joint. The new glasswork will not adhere as strongly to gelcoat as it will to raw glass.

    CSM is not the best fabric choice to tab stringers in. I describe CSM as being equally weak in all directions. It takes many layers and much thickness to get enough fibers bridging the gap.

    Current practice is to use 45° bi-axial cloth for tabbing. I suggest three layers of 1708. Place the attached CSM face down. The CSM allows the fabric to better conform to the substrate.

    There is often adhesion problems between wood and polyester. To avoid them, brush a coat of polyester resin on any raw wood and let it cure before laying glass.
     
  3. E350
    Joined: Sep 2015
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    Location: Sacramento River Delta, CA

    E350 Junior Member

    Thank you Blueknarr! When I searched TAB Plastics for :

    It returned:

    Knytex X-Mat DBM 1708

    [​IMG]
    And I may have some of that left over from a shower pan I did two years ago. I liked working with it. Is the Knytex product acceptable?

    Also, I was just thinking... Is there SUPPOSED to be a gap between the end of the wooden stringer and the transom to allow for expansion of the wood stringer along its length? Should I NOT fill the gap with a paste of cut up mat and resin and just bridge it with the 1708?
     
    Last edited: Jun 22, 2019
  4. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Yes that is the fabric I would use.

    The tabbing should extend onto hull/transom ( first 5" then 4" and 3"). The top of stringer should receive 3 layers and the layers should be stagered moving forward along stringer.

    The small gap between stringers and transom will be nice impossible to fill. I would ignore it.

    The larger triangular gap at the bottom could be ignored, filled or transmitted into a weep hole to allow water from outboard of stringer to drain into central bilge.

    Insert a soft tube into hole and pack filler around it. After filler cures, trim the tube flush before laying tabbing. Drill holes in tabbing while transparent. Smooth and finish with gelcoat/paint.
     
  5. E350
    Joined: Sep 2015
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    Location: Sacramento River Delta, CA

    E350 Junior Member

    10-4. Thank you for the layout width instructions. Once you used the term "tabbing" I searched for it here and saw what you described. I never knew that the technique had a name. The large triangular gap is at the transom in each of the stringers and they are, in fact the weep holes that Correct Craft built in. They are already glassed in place, but I will clean up the glass further and maybe add another layer of S-glass.

    One more picture, my wife says it isn't her best technique or at the most impressive part of the turn.

    DSC03834.JPG

    Skiing, sailing, fishing, kayaking, boating are not necessary for most of us to survive. They merely bring us closer to nature which, can bring us closer to our Creator, and makes it easier for us to experience Joy which he built into to us to choose. This forum and the guys and gals who freely give of their knowledge and experience -- helping us get our boats back on the water -- are truly a Blessing! Thank you Blueknarr! May you and yours have a Blessed Day, Weekend and Week!
     
  6. Yellowjacket
    Joined: May 2009
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    Location: Landlocked...

    Yellowjacket Senior Member

    Use epoxy. you'll get much better bond strength. The amount of epoxy you're going to use is minimal and you want to fix it right in the first place. Why save $5 and take a chance on it breaking or delaminating later? Makes no sense... Use the good chit...
     
    rwatson likes this.
  7. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    How much tape you need?

    I can send you some. Pm me. I have 4,6,8"
     
  8. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    There is no need to gap the stringer/transom interface. But if you close it up with glass or thixo; it would protect the wood stringer from ingress and rot.
     
  9. E350
    Joined: Sep 2015
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    E350 Junior Member

    Yellowjacket: I have used epoxy in the past for repairs, so it makes sense to me to use it for this application. It would be rare to have to add a layer of polyester resin/cloth over the top of the stringer to transom where I have used epoxy. I just checked my cabinet and I have some 4:1 General Purpose Marine Epoxy, but the can of 4:1A hardener is bad. So I will have to get some more. Blueknarr what do you think about using epoxy?

    Thank you, that is a great offer! It is appreciated. But I already have 2 yards of X-Mat which I will cut out so it will fold appropriately and be appropriately sized before I wet it out and lay it in.

    Sounds like a good idea to me. Will do.
     
  10. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    Epoxy will work.

    Be sure to cut your strips to maintain 45° orientation
     
  11. fallguy
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    fallguy Senior Member

    Can you explain? Do you mean the sides?
     
  12. Blueknarr
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    Blueknarr Senior Member

    The strips should be ÷-45%. Not along 0°/90° axis
     
  13. KD8NPB
    Joined: Mar 2018
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    Location: South Carolina

    KD8NPB Junior Member

    The laminate is so old, there would be no chemical bond with polyester resin.
    I would generally prefer to use 100% vinylester, because I hate epoxy.
    However, this is a case where using epoxy would be a good choice.

    All gelcoat must be removed via grinder before repairs are completed. The repair should extend a minimum of about 2 to 3 inches from the crack, although more is always better. In this instance, I would probably go 6 to 8 inches.

    Golden Rule of Glass ; THOU SHALL POINT THE FIBERS IN THE DIRECTION OF THE STRESS

    I would fillet the edges well to ensure the glass will wrap easily without air bubbles (air bubbles = no strength).

    I would generally prefer to do maybe 1 x BXM1708 , overlapping on the top of the stringer by about 6 inches. Then 1 x LTM3610, overlapping on the top of the stringer by about 6 inches.

    BXM1708 = 0.8 oz chop , 17 oz +/- 45 degree fibers
    LTM3610 = 1.0 oz chop , 36 oz 0/90 degree fibers

    The chop gives some anisotropic strength and a little stiffness. The directional fibers give isotropic strength and a lot of stiffness.

    Although, honestly, I'm a nerd, so I would probably vacuum bag the repair, because I hate rolling glass.
     
  14. E350
    Joined: Sep 2015
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    Location: Sacramento River Delta, CA

    E350 Junior Member

    KD8NPB: So, epoxy it is! But I can't find LTM 3610. Can you source it? I did read where chopped strand mat is not compatible with epoxy resin. My guess is that it is hard to fully wet out with epoxy, but I am not sure. I did read where Knytex X-Mat is compatible with epoxy. And I have successfully used it with epoxy in the past.

    How can you vacuum bag an object that you only have access to from one side?
     

  15. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Sorry, but 1708 is hard enough for this wetout.

    I apologize. I had thread confusion on the 45 degree bit.
     
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