Composite Chainplates. Vinylester Over Epoxy?

Discussion in 'Materials' started by Chotu, Mar 1, 2021.

  1. Chotu
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    Chotu Junior Member

    So I was on another forum posting that I wanted to hire a pro to lay up my composite chain plates using epoxy. The whole boat was made from epoxy, but I can’t go near the stuff anymore.

    more than one person suggested I just do the chain plate layup in vinylester, doing a secondary bond to the epoxy hull with vinylester.

    My experience says no. Must use epoxy. Especially with an epoxy substrate.

    I’ve had to find a lot of epoxy substitutes fitting out the boat after becoming severely allergic to epoxy and I have started to realize you could practically use children’s art project paste to stick things in place if you have a large enough bonding area.

    Is it as simple as checking the bond strength of epoxy and vinylester, then increasing the size of the chain plates to have a bond area big enough to make up the difference?

    it’s a catamaran so the chain plates must be able to lift the entire boat up into the air by crane. That’s the type of righting moment they produce.

    What should I do?
     
  2. bajansailor
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    bajansailor Marine Surveyor

    I just saw on another thread of yours where you found out that you were OK with vinylester - hence that would seem to be the logical choice to me.

    You would need to do some basic calculations to determine the size of the chainplate, based on what the maximum expected load will be.

    I would be very dubious though about relying on 'only' a bonded joint to attach the chainplate to the hull - especially when that chainplate is expected to be able to lift the whole boat up in to the air.
    Even if you overlaminate the chainplate - but then you need to do a lot of filling and fairing afterwards.
    I think that I would feel happier if there were mechanical fasteners (ie bolts) securing the chainplate.
     
  3. Chotu
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    Chotu Junior Member

    I’m sorry, you’re misunderstanding things.

    I’m talking about making composite chainplates. They are a million layers of uni and biax going every which way. There is no hardware, especially no bolts involved. No metal at all. Composite.

    The chain plate size is already determined for an epoxy layup. I’m wondering if it’s possible to do the bonding to the already built epoxy hull using vinylester .

    I know vinylester would be five for the chain plate itself. My worry is if the chain plate will properly laminate to the hull.

    The designer said simply, “epoxy would be better” in response to this question. Not a real answer, really. More like a suggestion.
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    If you are in contact with the designer - then why seek other answers here?
    Either the designer is able to support their design and mods done to it, or they can't?
     
  5. bajansailor
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    bajansailor Marine Surveyor

    Apologies Chotu, I guess I didn't express myself clearly - what you describe above is what I am thinking of.

    My only worry here is that even with a relatively large chainplate, you are going to put all of your faith into a single glued joint connecting the plate to the hull.
    OK, I know that there are some amazing modern adhesives, and that many parts of production boats are simply bonded together - eg grids and stringers are just glued in place without overlaminations - but my gut feeling simply says that I would prefer something more 'belt and braces', and for me that would be bolts.
    It is relatively easy to calculate how many bolts would be needed.
    If the chainplate is bonded to the hull with no overlaminations, then the joint is in shear - and I think it would be a bit (or a lot) more difficult to calculate the shear stress here.
    I am thinking you would need a minimum surface area of chainplate to be uniformly in contact with the hull, and use the formula allowable stress = Force / Area, where Force would be the force from the whole mass of the boat hanging on that chainplate, and the area would be the area in contact.
    But what allowable stress would one use for an epoxy joint?
    I was about to suggest asking Adhoc's opinion, but I see that he has just posted ahead of me!
    It rather sounds like the 'designer' has done a 'cop out' by vaguely stating that 'epoxy would be better'.
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    Indeed!!

    Find the worse case sales value - in the absence of any hard data - and use that value.
    Then use a FoS as a minimum of 5.
     
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  7. bajansailor
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    bajansailor Marine Surveyor

    I have not tried to do any calculations, but my gut feeling is telling me that these chainplates are going to have to be pretty impressively large in terms of surface area in contact with the hull, especially in view of how one chainplate has to be able to lift the boat into the air, and then applying a factor of safety of 5 on to the minimum scantlings required for doing so.

    Edit - a question please - what size cat are we talking about here?
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    The most pertinent question... as it leads to what weight -(force) - to allow for in the chain plates.

    A simple cursory review of online data for shear strength, such as HERE, suggests 25MPa.
    But of course knowing the exact epoxy to be used and its mechanical proprieties would be better to know.
     
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  9. bajansailor
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    bajansailor Marine Surveyor

    That is an excellent reference source Ad Hoc, thank you.

    Although I note that they say this :
    -----------------------------------------
    Lap shear strength is the ability of an adhesive to resist forces in the plane of the bonded surfaces. Bonded structural joints are typically designed so that the adhesive is only subjected to in-plane forces, resulting in shear stress in the adhesive.

    Compressive forces are transferred by surface contact alone and do not require any bond strength. Structural adhesives are typically less able to resist tension and, therefore, this type of loading condition should be avoided. Mechanical fasteners also work best when loaded in this way.
    ------------------------------------------
    Seems to me that they are suggesting using mechanical fasteners for this type of loading application rather than relying on the shear strength of the epoxy adhesive?
     
  10. Ad Hoc
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    Ad Hoc Naval Architect

    Well, looking at Gurit and their range, only suggests circa 2-3MPa for shear stress values.

    Fasteners are usually added to prevent peal at the ends, and then spaced "occasionally" along the length for good measure - in case of delamination over time between the 2 surfaces. .
     
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  11. trip the light fandango
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    trip the light fandango Senior Member

    I just got scalded for using the term shear incorrectly on another thread and basically told to keep my opinions to myself but I'm also here to learn. If Chotu wants to avoid mechanical fasteners[as in bolts] then why not use carbon tow or kevlar rovings soaked in vinylester as the through hull fastenings? Carbon wants to go hairy when soaked so splaying it out starfish like inside and outside the hull with some laminations over each hole will increase the glued surface area substantially. The epoxy will still need to be drilled but it is less inflammatory if you use water so there is no dust. I assume you would mix with fumed silica to increase the bonding properties.
     
    Last edited: Mar 3, 2021
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  12. Ad Hoc
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    Ad Hoc Naval Architect

    Im not sure what all that was about, however, if you wish to engage on issues that are technical in nature, then you must use the correct terms and definitions.
    Otherwise it is a free for all and no one knows what is being discussed. Thus one must use correct terms and definitions... and anyone that thinks that this is being pedantic, is just another petulant wannabe that simply doesn't understand and will only listen to those signing from the same hymn sheet as them, and thus why bother asking for advice/help then...go throw your toys out of someone else's pram!

    Opinions are great..everyone has them.... but in order to engage in a technical debate about your opinions/thoughts, please remember..definitions/terms mean everything!
     
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  13. bajansailor
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    bajansailor Marine Surveyor

    Another (perhaps slightly unorthodox) thought - would it be feasible to have the chainplates on the inside of the hull (coming up through the deck) rather than on the outside?
    This way they could easily be overlaminated to the hull and deck with no worries about creating a nice fair surface (which would be required on the outside).
    You could maybe use the hairy kevlar mentioned by Trip to create a form of 'pin' from the inside, if holes are pre-drilled in the chainplates (I assume that the chainplates have been made already now, or you are in the process of doing so?)
    And we are still waiting to hear back from chotu as to the size of the boat.
     
  14. Rumars
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    Rumars Senior Member

    It seems few have understood the OP's problem. His hull is foam/epoxy, and his chainplates were designed to also be laid up with epoxy. Problem is he can not work with epoxy anymore, so he is contemplating laying them up with vinylester instead. His question is how will the new vinylester bond to the cured epoxy, and is this bond adequate for chainplates.
    My answer is that it's a question for the vinylester resin manufacturer, or for a testing facility able to determine shear stress for the specific layup involved.
     

  15. trip the light fandango
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    trip the light fandango Senior Member

    Oh I apologised and appreciated being set straight, there was plenty of information to describe what I meant, what annoyed me was the poster preferring to ridicule rather than addressing the point. I suppose it comes with the territory, it's serious it could result in loss of life theoretically, so that's why you have just done it.. Synthetic rope could be used therefore presenting a measurable/ known strength, how well it wets out may need some testing.
     
    Last edited: Mar 4, 2021
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