Advice sought: re-glassing a cut bulkhead

Discussion in 'Fiberglass and Composite Boat Building' started by massandspace, Mar 15, 2022.

  1. massandspace
    Joined: Sep 2017
    Posts: 45
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    Location: Salt Chuck

    massandspace Junior Member

    I am in the position of having to join together a bulkhead that had to be cut. 30’ custom power catamaran.

    The original composition of the bulkhead is 3/4” foam with 36 ounces of glass/epoxy per side.

    So. In order to get back to the original strength (in tension), how much glass (thickness) would be needed, and how WIDE of a strip would I need to join the 2?

    This joint is not showing, so there is no need to grind back the seam….just asking if anyone knows how to get the bulkhead back to original tension strength….
     
  2. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    What is the configuration of the cut?
    Pictures?
     
  3. massandspace
    Joined: Sep 2017
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    Location: Salt Chuck

    massandspace Junior Member

    Configuration and pics not relevant to my question.

    Again. Is there any way to understand how wide of a “patch strip” is needed to get the panel back into the same strength, in tension?
     
  4. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    Your question is not a question unless there is substance to it.
    Did you cut a hole in the bulkhead, or just make a saw cut across it?
    Was it necessary to cut it to fit it in?
     
    hoytedow likes this.
  5. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Standard fg repair taper.
    Width would be eight to ten times the thickness.
    Much wider if carbon or Kevlar was used in original.

    Edit
    Above is the half width. 8-10 on each side of cut.
    8 for inches and 10 in metric.
     
    hoytedow likes this.
  6. massandspace
    Joined: Sep 2017
    Posts: 45
    Likes: 0, Points: 6
    Location: Salt Chuck

    massandspace Junior Member

    Let me ask in another way….

    Imagine you lay up a flat panel. 4’ by 4’ by .75” foam with 36 ounces of BIAX and epoxy on both sides. You then destroy it by pulling it apart (tensioning it) from opposite sides and record the force needed.

    You then lay up an identical panel. Then cut it in half (two 2’ by 4’ by .75” halves). So now you want to glue it back together with 2 strips of BIAX tape (one each side) to get it back to the same tension strength if destroyed in the same way….what weight cloth (36 ounce?) and how wide of a strip (how many inches) would you need to use to get back to the original strength?
     
  7. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    With respect, photos are always useful to help to describe anything - they usually do the job much better than any amount of written words can do.
     
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  8. massandspace
    Joined: Sep 2017
    Posts: 45
    Likes: 0, Points: 6
    Location: Salt Chuck

    massandspace Junior Member

    I have plenty of photos, but I am simply asking a general question about tension strength on a cut panel….please read the question carefully and ask any questions…..and if you have a definitive answer that is what I am after….
     
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