What joint to use in bulkheads??

Discussion in 'Boatbuilding' started by CatBuilder, Jun 3, 2011.

  1. CatBuilder

    CatBuilder Previous Member

    I'm not following you, PAR.

    I'm not using any kind of real adhesive in the Payson Joint according to the diagram, but rather a bog. The diagram shows a rather thick bog between each layer of glass in the joint and surrounding the two "ears" of plywood.

    My entire boat is made from balloons and colloidal silica based bog in many ways. It is used to join pieces of foam core to one another, used to cove in bulkheads, used as a syntactic layer between layers of triaxial...

    I'm sure it's fine for this bulkhead joint, if it's used to hold the actual bulkhead to the hull, no? :confused:

    Hoyt: The picture is in post #34 in this page. You said "good job, it looks strong". Remember? :D
     
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The way a Payson joint works is through the appropriate amount of 'glass fabric for the thickness and thickened epoxy. The thickened epoxy isn't just for cosmetic considerations, but replaces the wood that was removed in the grinding (planing, belt sanding, etc.) process. The fabric (preferably 45/45 biax) brings cross grain (cross joint) strength to the joined parts.

    Bog is a fairing compound term used by Australians. Fairing compounds have no strength, just offering an easy to sand, light weight surface, of which most is removed in the fairing process.

    The whole idea of joining two pieces together with the Payson joint is to physically make them as one piece. I can't imagine joining bulkhead sections with "Bondo" type of materials, even if it is lightly loaded.
     
  3. CatBuilder

    CatBuilder Previous Member

    That really confuses me because my designer disagrees. He suggests using the stuff as I mentioned. The one that really gets me confused is that he suggests using it as a syntactic layer between multiple layers of glass, indicating its use as an adhesive.
     
  4. hoytedow
    Joined: Sep 2009
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    hoytedow Wood Butcher

    "Picture!?" was in reference to the highlighted area. Sorry I didn't communicate clearly.
     
  5. CatBuilder

    CatBuilder Previous Member

    Whoops! ha ha ha Gotcha.

    Here you go!
     

    Attached Files:

  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    You seem to be making these sorts of "decisions" all over this build, then asking for recommendations and solutions. On a project of this scale, it would seem to me the wise thing, would be to become quite familiar with epoxy, it's typical reinforcements and application techniques specific to your build. "Learning on the fly" as you are is fraught with problems, as you learn (the hard way) about techniques, materials, methods, all of which can be avoided with some research. I don't know of anyone that would recommend a "bog" as you call, it for an adhesive. These tend to be brittle under load, crumble under pressure and generally don't have the physical properties necessary for a reasonable "glue" application. Lastly, amazing at it might seem, designers can be wrong sometimes. I was once, about 20 years ago :D.
     
  7. CatBuilder

    CatBuilder Previous Member

    I'm not sure what you're talking about where I have made any mistakes in the build. You are saying I don't understand epoxy and its applications techniques for my build? What?

    It's 1" thick, 6lb Core Cell with 34oz triax skins on both sides. Corecell strips are held together with microballoon and colloidal silica, then glassed over. All glassing is done with SilverTip laminating epoxy. Any instances where you need to bond more glass on top of the 34oz (for structural reinforcements) are done by filling the weave of the triax in with the same microballoon/silica mixture, then more glass is laid on top. Holds a hell of a lot better than leaving air gaps in the weave of the triax, no? Peel ply is also used extensively. Bulkheads are 12mm BS1088/Lloyd's Okoume. Bulkheads that are not part of beams to hold the boat together are coved in with bog only. Bulkheads that form part of the structure and span the hulls are bogged and taped with biax.

    Where can you point to something that is wrong with my build?

    There is a sistership out there that's been actively cruising and chartering for 18 years - rode hard and crossed several oceans. She's still chartering in the Caribbean today.

    I'm thinking if it was good enough for that boat, it's going to be good enough for mine. That's my line of reasoning, anyway. That, and the USCG issues COIs for these vessels for passenger service and has no problems with the build methods. Additional bulkheads are required, however, for the COI.

    I guess it's your opinion that the designer is wrong, which you are entitled to and I do respect.

    At the same time, Kurt Hughes is probably the 3nd best known 2nd generation catamaran designer in the USA (after Morelli and Melvin and Chris White). I'm going to have to go with his recommendations, as he's the guy that did all the modeling and materials analysis for my particular build and knows the actual numbers involved.

    Thanks for you help with the Payson joint idea. Much appreciated. I just don't understand where you are coming from saying I'm not building this boat correctly. It's done like this by everyone - all over the world. Farriers are built pretty much the same way, for example.
     
  8. fg1inc

    fg1inc Guest

    The designer probably knows very well what he's doing, catbuilder. However, as an illustration of Par's point here, I would suggest a simple test. Laminate a test coupon about 3 inches wide and 12 inches long using 3 layers of bi-ax with a quarter inch of "bog" between each layer. Let it cure a couple days and then flex it to failure. Observe carefully where the failure begins and how it propogates.
     
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    A better test would be a direct comparison of milled fibers and silica (mixture) on a substrate and the bog mixture mentioned above. Also wood flour and silica, cotton flock and silica, etc. I think (I know) you'll find the smooth (microscopically) particulates compared to the rough/fibrous particulates just can't stand up against strain. I know of no professional using fairing compound filler materials in the their adhesive mixtures. At least not to a high percentage, though often some, just to ease finishing a bit.

    The core strips aren't being glued together with this mixture, it's just filling a void. You can use anything you want for this task, mashed potatoes will work, so long as you seal in down good with a laminate or other bonded substrate. A bulkhead, even a lightly loaded one, is a different matter and should be glued (structural filler), unless of course this too will receive a substantial laminate, in which case the core (plywood in this instance) is supported and bonded with the fabrics and the cosmetic filler just holds it until the laminate gets there.

    I'm not trying to insult you Catbuilder, it just seems you've gone into this project less then well equipped or well armed with understanding and forethought. Again on a project of this scope, planning and forethought can save hundreds of hours of effort and thousands of dollars in materials. It's not necessary to list the "interesting dilemmas" you've posed, but most could have been avoided. Of course forethought and planning just aren't the hallmarks of a back yard build, though on a project of this scale, maybe a good investment.
     
  10. CatBuilder

    CatBuilder Previous Member

    I already did that at the beginning of the build. Don't you guys remember discussing "bog frosting?" fg1inc, I know you were on that thread. I made up test samples every which way from Sunday and found that the bog frosting was a better syntactic layer than neat epoxy. Neat epoxy left too many voids between the weave.

    We're not talking about biax here, we're talking about 34oz triax. Entirely different animal.

    Why is all this coming out now? Where were you when I moved forward months ago?!?
     
  11. CatBuilder

    CatBuilder Previous Member

    I am using what my designer calls "structural bog." What the hell do you use to cove in your bulkheads?!?!

    You say you don't intend to insult me, but you say:

    "You seem to be making these sorts of "decisions" all over this build, then asking for recommendations and solutions."

    and

    "Of course forethought and planning just aren't the hallmarks of a back yard build"

    and

    " it just seems you've gone into this project less then well equipped or well armed with understanding and forethought."

    If those aren't insults, what are they? :mad:


    Where the F do you get off calling my build a "backyard?" There is no backyard about it. It's being built in a boatyard with professional builders checking in on the progress on a daily basis. You are the only person who has given me a hard time.

    This entire thread is complete BS.

    You have no idea what you're talking about. I trust Kurt Hughes over some no name designer any day. That's why he doesn't come on these forums. He says you all don't know sh*t and I'm starting to believe he's right.

    There are much more informed places online to ask questions, where people understand how to build these boats.

    I will now be posting exclusively in those areas.

    No more updates, no more questions, no more participation in this board.

    I don't need this kind of BS when I'm in the middle of a build. Just because you aren't actually doing anything right now and have all the time in the world to nit pick things apart, doesn't mean you have the right to.

    Good bye, for good and go F yourself.





     
  12. fg1inc

    fg1inc Guest

    Wow! Ok! Stick to your guns Cat, I'm sure everything will turn out fine. The only point I'd like to make is that the advice you get on this forum and all others is often bogus. We've done our own testing for 30 years now and have been surprised at the results we get versus what we've been told. When in doubt....TEST. It's easy, it's cheap, and you'll learn more than from any other source. Best of luck and fair winds to you.
     
  13. rasorinc
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    rasorinc Senior Member

    `Hi CatBuilder, just because you are angry at one person don't run from the folks who are following your build and will miss your postings. I'm the one that said lift it with a strongback and Hoyt drew out a great picture of it. You had never heard of a strongback before but it worked. A poor mans Beam. Now Par was asking questions about a product your using and questioned your judgement. OK to get angry using non-swear words but he has built more boats than you and and a dozen others and offers valuable advise. Home built, back yard built means you, a non-proffesional boat builder and are doing it with advise of others and everyone accepts advise. Par has gone out of his way to assist me by way of private messages and I greatly appreciate it. Richard, a member awhile back gave great advise also and could be quite curt in his speech though spoke english perfectly (he is german) He blew up at Jeff and now is off the forum---Our Loss. He had great personal sadness that came into his life ( lost his ex. and twin daughters in a car accicent) and went on a language spee(dirty)
    Anyway Par is a good man and likes to help and if you do not want his help that is fine but do not cut off your friends who are closely following your build and admire you for taking on such a large project. Stan
     
  14. Nurb
    Joined: Jan 2011
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    Nurb Junior Member

    Maybe toxic fumes :(
     

  15. hoytedow
    Joined: Sep 2009
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    hoytedow Wood Butcher

    Aw Cat, you don't mean it, do you? There was no malicious intent, I'm sure. Honest criticism from PAR, meant to be helpful, perhaps overly blunt. Come back, please and let us enjoy the fine progress on this fine vessel. We have all been going to school with you on this build and more than once I was shown to be wrong in my opinions.:(:(:(:confused:
     
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