Confused on the order to do layup

Discussion in 'Fiberglass and Composite Boat Building' started by Buckeye492, Aug 12, 2019.

  1. ondarvr
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    ondarvr Senior Member

    3” is tight and at the low end of acceptable, 4”-5” is preferred.
     
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  2. Buckeye492
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    Buckeye492 Junior Member

    Attached is a picture with dimensions & showing where the other cracks I was speaking about are located. After looking more closely, I would agree that wrapping around the bottom does not appear to be a good idea as the 1st chine is in that area. So, the next question is how do I address it without wrapping? Just grind & fill with Epoxy & cabosil? As far as reinstalling the cutout panel I am not quite understanding. I think you're saying 1-3 layers of 1708 then fill the rest with epoxy & cabosil? If you need other dimensions or views let me know.
     

    Attached Files:

  3. fallguy
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    fallguy Senior Member

    It doesn't look like you ground the margin to good glass, but the picture quality is very poor.

    Do you have access to the front edge of the well? Top only or bottom, too? The coosa needs to be bolted into position to cure, then you remove the bolts before full cure.

    How are you going to bond the coosa to the old glass? It must be done exceptionally well since you are only gluing the knees to the transom and not tabbing them.

    Once the double coosa is applied, how thick is the edge versus the coosa? For example, the coosa is 1.54" bonded and the edges are 1.4 or 1.6".. Are they flush or lower or higher?

    Also, this transom is not high; you really need to wrap it up and over since the margins are so light. I am guessing you have a motorwell about 7" deep. You would be able to radius the top of the coosa and old glass say 3/8" radius transom top and grab the old glass and that would help. This way the repair has a good hold of the existing hull. Ths would require removing the gelcoat in the well aft face.

    Then when you glass the exterior; you wrap three or four pieces of cloth from the well up and over.

    When I built the transom on my boat, I actually overwrapped both directions. And then you stagger the ends of the glass 50mm to avoid a hump. You could even try that. So three layers up an over main exterior laminations and three layers from the well up and over. They can be done as secondary bonds (separate days). But each side needs to be primary.

    You have a sort of subpar plan going there otherwise.

    I suggest you take a picture of the motor well.

    The way you stagger would be say 6",4",2" over into the well and then stagger from the well bottom say 7,5,3 and up and over the transom 8,6,4. This would help where the most torque is applied by the engine.

    I am stil not a big fan of the approach, but I can live with it overwrapped.
     
  4. fallguy
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    fallguy Senior Member

    D3205DA5-2249-4827-8786-D0EF17CC4970.png Here is a cross section. Black s transom and motorwell.

    Green is main glass over well 6" and 4".

    Red is xtra glass from well starts at well bottom say 7,5 and goes to 8,6.

    I would do 3 layers at least. Not a naval architect, mind youz

    Picture is two layers for finger drawing simplicity only.
     
  5. fallguy
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    fallguy Senior Member

    AB99ED00-D5EA-4360-8478-C37B90E4CB62.jpeg Here is a picture of the inside wrapped over first. It is 3-4 layers on 2" staggers with peelply over it all. This glass is laid over the entire transom inside and onto the hull sides as well. You can grab the motorwell instead.

    We peelply to improve adhesion for the outside layer. You need plenty of radius or the glass won't take the corners.

    Provided for clarity...
     
  6. Buckeye492
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    Buckeye492 Junior Member

    I have not started grinding yet as I wanted to have my plan laid out on exactly what I am going to do. Which I have an good idea right now, but nothing is concrete yet. Yes, I do have access to the splashwell. It is about 7" deep as you mentioned. Just didn't have time to take a picture. I do like the idea of wrapping over the top for the added strength as long as the over all thickness doesn't present problems mounting the motor.

    To bond to the old glass I was planning to use Vinylester Resin & Cabosil.

    Not sure I understand this question: "Once the double coosa is applied, how thick is the edge versus the coosa? For example, the coosa is 1.54" bonded and the edges are 1.4 or 1.6".. Are they flush or lower or higher?". Edge of what? The original transom thickness was 1 5/8" w/ 2 pieces of 3/4" plywood & some type of foam added to fill gaps. Not sure if that helps.
     
  7. fallguy
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    fallguy Senior Member

    E212D6A0-6EAC-4803-9C46-3407950DF63D.png The existing hull.

    Is the existing hull in the same plane as the coosa once applied or proud or recessed? Or are they slightly nonplanar, like 1/8" difference?

    This is a top view. The hull is black the coosa is blue. How do they mesh?

    You really need to overwrap.

    If you end up thick; you grind the tabs off the engine mount is all.
     
  8. fallguy
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    fallguy Senior Member

    0E11A03B-6154-4EDF-A796-E1BB101FF636.jpeg Here is a picture of a non standard mount. The arrow points to the tab that limits the transom thickness.

    You will probably be fine.

    If not, you grind off the tiny bit.
     
  9. Buckeye492
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    Buckeye492 Junior Member

    Slightly proud. I am going to take your suggestion & overwrap into the splashwell. Thanks for all the information!!
     
  10. ondarvr
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    ondarvr Senior Member

    Wrapping over the top will make it stronger, you don’t need to worrying about thickness, the small tabs are the only things that may interfere, you can make a small notch in the glass if needed to clear them.

    Don’t stress over it though, remember, this boat survived many decades of abuse with less glass, and and a weaker form of it, so whatever you do will be an improvement over new.
     
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  11. fallguy
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    fallguy Senior Member

    A friend of mine knew four boaters that died from a transom failure.

    It is possible to mess this up. I hate to contradict ondarvr, but if people think they can do anything and make it better; that would not be true. I am sure he means this poster; not any repair.

    I understand how this can be polemics, but if you failed to bond the coosa to the existing hull or overwrap, for example; it would probably mechanically fatigue and fail at the small margin. Probably in rough seas and the worst moment.

    The only reason I mention is so others realize this is a critical piece.
     
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  12. ondarvr
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    ondarvr Senior Member

    I’m not exactly sure what you are talking about here.

    We are discussing this boat, repaired with these materials, and in the amounts/thickness he mentioned.

    It has nothing to do with the details of anybody else’s project.


    Now here’s some recent testing I did.

    We have a customer that buys a bonding putty from us, it was developed years ago for this customer.

    There were some concerns on my part about how it was being used in their shop, so I did some testing.

    I used this putty plus a couple others in different ways to see what effect it had on the bond strength.

    The results surprised us a bit at first, but made sense.

    To shorten the story, it made no difference in the test results what catalyst level was used, or when I upgraded to what should have been a stronger better bonding putty.

    We used an Instron machine to test the bond.

    What happened was that our normal bonding putty, even when not catalyzed as we recommend, was stronger than the laminate it was applied to. (typical laminating resin to build hulls).

    This resulted in all the failures being located in the original laminate, not in the putty or the bond line.

    The same thing frequently happens when epoxy is used to do a repair on polyester, the part can still fail in almost the exact same way, at the same stress level, because it’s the original laminate failing.

    If you used VE it can fail at the same level of stress as epoxy because it’s stronger than the original laminate too.

    You get a more similar strength to the original laminate when using a polyester resin to do the repair.

    I’m not saying that these resins are all equal, it’s just that you may not see an improvement in the strength of the part when upgrading the new materials.

    These older laminates can get weaker as they age due to fatigue and water absorption. So they may have been stronger 40 years ago than now, resulting in an even greater difference in the strength of the new material being applied over it.

    This is why using epoxy may not really be improving the overall outcome of the repair.
     
    Last edited: Sep 1, 2019
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  13. fallguy
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    fallguy Senior Member

    Not about epoxy vs esters.

    Just about 'any' repair being better.

    Kindest regards and the highest respect.
     
  14. ondarvr
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    ondarvr Senior Member

    The reason I said he didn’t need to stress about it is because he is significantly overbuilding it compared to when new, better glass, better resin, plus thicker.

    If another person reading this is doing the same thing they don’t need to stress about it either.
     

  15. Buckeye492
    Joined: Aug 2019
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    Buckeye492 Junior Member

    So I am curious. I was doing some reading the past few days on the order of the layup. I've read start with the widest piece of glass & get progressively smaller as you build it up. This doesn't make sense to me because if the first layer fails, everything fails. My plan was to start small & get wider as I built it up. In this case, if the first layer fails, there are the remaining layers still bonded to the surface. Am I missing something?
     
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