Repairing foam cored catamaran with solid glass. Hard spot?

Discussion in 'Fiberglass and Composite Boat Building' started by Smj1, Jun 30, 2018.

  1. Smj1
    Joined: Nov 2015
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    Smj1 Junior Member

    Hi, first post here.
    We recently purchased a foam cored performance catamaran that has lightning damage. I told the yard I wanted the hull fixed as original, Divinycell core, vinylester resin and biaxial glass. Instead of cutting out the old core and replacing they ground out some of the core to the inner skin then beveled the remaining foam and glass to a 12:1 ratio, filled with CSM then put 2 layers of biaxial on top, in other words a solid fiberglass repair. This is a very lightweight 40’ performance catamaran and I believe doing solid glass repairs is going to introduce hard spots into an engineered design. The biggest repair is about 6 square feet. Any thoughts?
     

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  2. fallguy
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    fallguy Senior Member

    I would say hogwash, but I am generally more polite.

    I am building a new cat and it has a solid glass section next to a cored section.

    Solid sections can be intertwined with cored sections all the time and for many reasons. Certain rules even require foam to be omitted in places on certain builds.

    That said; if you didn't trust the yard; it would have been wiser to hire a consultant to spec the repair.

    It might have been nearly impossible to add core, if for example, thermoforming into a mould were in the original build. Keep that in mind, too.

    The only thing is cores are added to reduce weight, so the repairs are adding weight. Touche'. You own a lightening damaged boat; deal with it.
     
  3. fallguy
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    fallguy Senior Member

    Good explanation about hard spot here.

    Marine Surveying : Hull Design Defects - Hull Failure Part II - Boats and Yachts Surveys http://www.yachtsurvey.com/HullFailP2.htm

    It did not look like your repairs were on the bottom. If they were or not; then the possibility of some hardspot on a bulkhead or frame does exist. If it were built well originally, any hardspot concerns would have been addressed by using core pads at the hull and bulkhead intersection in the original build. Such pads would not have been removed using the repair method you state.

    It can be true that the original build decided hard spot was no concern since they had a foam hull. If so, then you may have a small section of hard spot in the repair.

    You would need to know the specifics of the bulkheads or transverse framing to determine whether or not this is true.

    And if it is; it would probably be a very small section of hardspot.

    Sounds like a nice boat.
     
  4. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    Welcome to the forum

    If Fallguy says hogwash when he is being impolite, then I'm in trouble.

    He is spot on.

    The repair is unfortunate in many ways. But "hard spots" ain't one of them. Yes weight was unnecessarily added, but not much, couldn't be more than five pounds. Even at ten, what percentage of overall gain is that on a fourty footer?

    I understand the "fillings" if core is only surface damaged. But onse it was fully removed, then core replacement would have been easier shaping (fairing) than csm.

    I am more concerned with shrinkage. I suspect that a repair that thick will need to be refaired in a year

    Do you know why the yard changed repair plan? What is it doing to make you happy? Few businesses want customers walking away dissatisfied.
     
  5. Smj1
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    Smj1 Junior Member

    Thanks for your reply.
    My thoughts were the foam cored hull wouldn’t be as stiff as the solid glass repair therefore putting undue stress on the area where the original hull and repair join. I’m sure the 12:1 bevel in both foam and glass would help to alleviate this stress. The core is Divinycell grid scored so no thermoformimg needed.
     
    Last edited: Jul 1, 2018
  6. Smj1
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    Smj1 Junior Member

    Thanks for your input as well!
    The core was taken down to the inner skin in quite a few places and I could fully understand the type repair they did if the core was only dished out rather than completely removed in spots. I fully agree the repair would have been much easier to fair if the core was replaced as original. I haven’t thought of the shrinkage aspect.
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    I think I'd be more concerned about what other damage the lightning strike might have done, that isn't so obvious to the eye, rather than supposed hard spots from the repairs, I don't see that being an issue. It has just introduced a little extra weight, but one wonders what else is out of sight. Maybe there is some kind of ultrasonic testing method to establish that, but I really could not say how definitive that might be. Delamination would be an obvious concern.
     
  8. Smj1
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    Smj1 Junior Member

    The hulls, mast and crossbeam were thermal imaged and seemed to be pretty accurate pointing out the damaged areas.
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    Has it come under the inspection of a marine surveyor ? I'm guessing some are familiar with the effects of lightning on GRP structures, to know how best to establish if things are safe and sound.
     
  10. Smj1
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    Smj1 Junior Member

    Yes, a full survey with thermal imaging was done after the lightning strike. All supposed areas impacted by the lightning strike have been ground out back to good laminate and foam. Those areas have been repaired as previously stated. The surveyor inspected those repairs and thinks they should be satisfactory. The boat designer seems to disagree. Maybe I’m overthinking it, but I’d like to go back with the best repair for this type of construction. Thank you for your input.
     
  11. SamSam
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    SamSam Senior Member

    Since that boatyard doesn't seem capable of following simple instructions, I would wonder what type of resin they used for the patch they did.
     
  12. SamSam
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    SamSam Senior Member

    The 12 to 1 slope looks pretty inconsistent, especially on the glass which is where it actually counts.
     

  13. Smj1
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    Smj1 Junior Member

    Thanks, I am usually pretty detail oriented but you are absolutely correct.
     
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