Best method for bow/top deck collision repair

Discussion in 'Fiberglass and Composite Boat Building' started by douglee25, Jun 9, 2011.

  1. PAR
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    PAR Yacht Designer/Builder

    The only time mat is useful in an epoxy laminate is as the very last layer. I do this often to prevent fabric weave print through and make fairing a bit easier.
     
  2. douglee25
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    douglee25 Junior Member

    In the past I've typically used the biax with mat for heavy build areas. The biax I purchased has the mat stitched not glued to the biax so it is compatible with epoxy.

    Do you agree with that logic?

    Doug
     
    Last edited: Aug 1, 2011
  3. PAR
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    PAR Yacht Designer/Builder

    Again, epoxy laminates do not need, nor is it desirable to incorporate mat. The only time I find it useful, is to prevent print through in finish coats. Mat is a bulking material, which is necessary with polyester and vinylester resin, but not with epoxy. It's not a compatibility issue, it's a waste of materials issue. If you use mat, you'll being wasting resin and adding the bulk of the mat for no apparent reason. It just makes for a weaker, thicker, heavier epoxy laminate. So, it's your call and you can use as much epoxy as you like. If you employ mat, you'll use a lot more then you needed to for the same strength.
     
  4. douglee25
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    douglee25 Junior Member

    I appreciate your advice. I'm sure you have a ton more experience than I do and I am here to learn. I'm not going to disagree with you, but for the size of the repair we're doing, I don't really think weight is going to be a concern. I will keep you posted on the progress.

    Doug
     
  5. PAR
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    PAR Yacht Designer/Builder

    Weight isn't an issue on small repairs, but strength and material use certainly are. I'm not sure why you're marrying yourself the the mat, but it uses literally 3 times the resin to wet it out, then the same weight cloth and offers only minimum strength the the laminate. The resulting layup is brittle, weak and heavy.
     
  6. douglee25
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    douglee25 Junior Member

    Ok thanks for the feedback.

    Doug
     
  7. douglee25
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    douglee25 Junior Member

    OK another update -

    Bulkhead was totally ground out and prepped for the new piece later on.

    The backside of the large crack on the lower side of the hull has also been ground down in order to lay a few layers of glass for additional strength.

    The molded part for the top side has been fitted and ready for glassing into the exisiting top deck.


    Question - On the molded part, is it better to build up layers to the required thickness while the piece is off the boat, then grind the exisiting deck and the new piece (after it's cured) and glass into the hull? Or is it better to fit the piece into the top deck, grind back the exisiting top deck, then build up to the required thickness and while adding glass to the joint between the two pieces?

    Thanks again.

    Doug
     
  8. douglee25
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    douglee25 Junior Member

    I made a decision to install the molded piece on the boat first, secure it in place with screws and epoxy, build up the center of the patch, and then start to lay glass into the existing portion of the boat as we got closer towards the required thickness vs. building up the patch with glass on the ground. It was good that we decided to do it this way because we were able to get more of the curvature of the hull flexed into the patch.

    Yesterday we got the patch trimmed, epoxied, and screwed into place. I thought I had the epoxy mixed thick enough where it wouldn't run, but I was wrong. It was just so hot that it was a little more runny than I had hoped. We will go back and grind off the bulk of the excess resin before we start laying glass on that area.

    On the lower portion of the hull, we got 5 layers of glass down. The back side is prepped for some glass as well. I think I said before the bulkhead is ground out and we're making a pattern right now out of foam to see if we can sneak the piece in without cutting a slot from above through the seat support. If it does require a slot, it shouldn't be a big deal. We will just cut a 1" slot and drop the bulkhead down into place. Then we will tab it in.

    Anyway, onto the pictures. I don't have the picture of the foam piece that I sculpted, but it's under those couple layers of glass here.

    [​IMG]

    [​IMG]

    Here is most of the bulkhead removed on the interior of the boat just prior to grinding the rest of it out.

    [​IMG]

    Here are a few pictures of the cracks which were ground out.

    [​IMG]

    [​IMG]

    [​IMG]

    Here is the patch fitted into place with just screws at the moment.

    [​IMG]

    [​IMG]

    [​IMG]

    And finally here is some shot of the glass laid up on the exterior of the hull along with the patch epoxied into place.

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    That's all for now. I'm going on a trip for a little, so progress will probably slow unless my buddy feels up to tackling some more on his own.

    Doug
     
  9. themanshed
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    themanshed Senior Member

    That is a nasty bow crack 12:1 will fix a crack but I'm not sure it will give the strength of a laminate lay-up say a 1,500 lbs boat hitting a wave at 40 mph. I would do a lay-up behind the crack at least a foot on each side of the crack then grind out again from the outside to the new lay-up getting rid of all cracked glass and build up the outside. One other thing I would use Epoxy not a Poly based resin. The white inside skin with the holes is coremat and has no strength you should have ground past the coremat. In the second from above picture the repair glass stops on the coremat and does not continue to the old skin. It looks like you have at best a bond to just the outside skin (looks like mat) above the coremat. Sorry to seem critical of your work but it looks like you have a band-aid on the outside and I would be cautious to take that repair in the water at any speed or pounding. Hope I'm wrong and the pictures do not do your work justice. Boat repair unlike other repair jobs has to look good but be able to take the designed loads of the piece prior to the repair work.
     
  10. douglee25
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    douglee25 Junior Member

    It may be hard to discern from the pictures, but we ground out much further than 12:1... I would estimate almost 12" wide in some areas. We are reinforcing on the back side like you suggested as well as using epoxy for the repair. We hope to resume the repair shortly.

    Edit - The coremat that you're seeing is only at the edge of the repair where is has been faired. Most of it has been ground out. It looked to me like the coremat was used near the very last layer during the original layup. What you're seeing also is only about half the layup required for the lower portion of the bow, so it's just not near completion yet. To lay it up all in one shot would generate too much heat. The hull ranges in thickness from 1/4" all the way up to 1/2" or so in some areas. I suppose we could have glassed from the backside and then ground out on the frontside, but we opted to glass the backside last. I guess there's a few different ways to skin a cat as they say. If you saw the repair in person, I think you would agree that it hardly looks like a bandaid fix so far. I do appreciate your comments and insight though.

    Doug
     
  11. themanshed
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    themanshed Senior Member

    Sounds good my other thought is the inside and outside skins should touch each other so the load is transfered, get rid of the cracked glass all together
     

  12. douglee25
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    douglee25 Junior Member

    Good point. I will do that on the inside repair.

    Doug
     
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