Vacuum Bagging On Plywood and Balsa Permeation?

Discussion in 'Boatbuilding' started by zstine, Jan 29, 2021.

  1. gonzo
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    gonzo Senior Member

    Infusion has a very limited time. If you don't get the whole laminate properly wetted before the resin gels, the only solution is to cut up and burn the whole thing. If you want a long time limit, prepregs are the answer.
     
  2. zstine
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    zstine Junior Member

    With infusion, I can set everything up without resin and pull a vacuum, do a pressure drop test and spend days getting my bag leak free. There's no time limit for how long I wait before I being mixing and infusing resin into the bagged layup.
    The real issue is how the resin flows through the matrix. There are ways to mitigate risk with that, like adding a few strategically placed infusion ports to add more resin to certain areas if needeed. Or making the resin header in several sections with shut off valves so you can control resin propagation in different areas of the boat.
     
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  3. fallguy
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    fallguy Senior Member

    All you do to seal test is run the floor flange seal side 6" wider and then you can cut it at the butyl and still have enough for the next go. The ends will be some trouble, but the bag can also be repaired with butyl and another piece.

    I think infusion of half the hull at a time might work well. He might have to help the flow manually, so seeing it might be important. It is out of my wheelhouse to speak to the infusion business, but 24' half hull is pretty big, so 2 hour epoxy if you wet bag. Many slow cure epoxies require post curing, and that can mean the entire boat needs cooking. I have done this; it is complicated. If you paint the boat white; you can probably avoid post cure, or you could use some heat blankets and post cure in sections versus the oven method I used.
     
  4. gonzo
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    gonzo Senior Member

    That assumes that nothing goes wrong. In my experience, there are often leaks that appear and have to be fixed as you go. Are you planning on working alone?
     
  5. zstine
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    zstine Junior Member

    I really haven't gotten to the point of deciding if I should call in help. I'm sure i can find inexperienced friends, but I'm not sure if they will hinder or help. I'm planning this build over the summer since my shed is not heated....
    I am curious why you find significant number of leaks after you start the resin flow? If you have pulled vacuum and passed a leak test then the system is shown to be air tight. What causes leakage when you start the resin flow? or do you just find small air bubbles getting in that you have to deal with?
     
  6. fallguy
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    fallguy Senior Member

    Be forewarned that you cannot wetbag even half the job singlehanded on 60 minute epoxy. Even closing the bag will be trouble alone.

    You can leverage inexperienced help. I have done it plenty.

    you prepare mixes a,b,c resin and hardener and then you walk through the entire process so the help has an idea of what is coming and most likely you will need to wet the substrate if you wetbag; this takes about 40-50% of the amount which will be about 110% of the glass weight; if you need to wet 24 feet of substrate; anyone who knows how to roll paint can do so...they can also mix batch B while you are doing other stuff like rolling out the glass over the top; so there are actually lots of ways to leverage unskilled help and they only get in the way under poor command structures

    If you simply plan on mixing 3 batches of epoxy, stirring by a third person saves 4 minutes; roller help on such a large project saves probably about 15 minutes because the substrate gets rolled and the top gets rerolled and if you have multiple glass layers, even more.. We wet bagged 34'x2.5' flat panels using a 2 hour epoxy with two fast guys and a slow one and we had bag times from 110 to 73 minutes for two sided laminates. You will be covering more square feet and a more complex surface and so you will need 3 people minimum to wetbag at 50% of the boat and 2 hour epoxy. You won't have to wet the core like we did and you won't necessarily need to flip 34' long core panels, but you will be really pressed hard to finish in 60 minutes.
     
  7. fallguy
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    fallguy Senior Member

    8F254CC8-E57C-491D-A07C-7EA176D90B41.jpeg 4DFCCC48-74EE-4109-97D2-1C8A9DC4962E.jpeg I would not start the panels without two helpers. The bottom panel is a 15'x3 footer and I still had two helpers for 45 sqft. Our bag times were not recorded on these, but we were closed in about 60 here. The guy with the rubber mallet is a good guy, but turtle and hare turtle slow...-a good friend tho; he was messing around with the mallet
     
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  8. Howlandwoodworks
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    Howlandwoodworks Member

    Zstine,
    I can tell you are determined and you realize this is a heavy lift project.
    I found this construction technique has a steep learning curve, a long term payback period / (SIR) Saving to Investment Ratio over a traditional construction methods.
    I did it anyway for just small woodworking project under 6'x10' flat panels and even smaller curved project with a 5 CFM vacuum pump, kit, bags, etc... for just under $1000, 25 years ago.
    There are some Similar Threads below this one that can offer some perspective on vacuum infusion for boat hull.

    There was a hot molded veneer technique that was phased out with fiberglass production after the WWII. I have a tiger striped mahogany 1954 International Jet 14' Class sailboat made with this technique. Some airplane like the Mosquito and Spruce Goose were hot molded veneered also. You would need a very large vacuum autoclave for this and it would be really bad on your (SIR).
    I hope you reach your goals whatever they might be and most of all that you can find joy in the process.
     
  9. wet feet
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    wet feet Senior Member

    The post from fallguy is a great illustration of what can be achieved.A panel of that size on a flat ,impermeable surface in 60 minutes is fairly comfortable.A hull 25 feet long and with a girth of say 13 feet is a much bigger laminating project perhaps 6 times the surface area.Several helpers would be essential if wet laminating and they ought to have a little experience or at the minimum a chance to observe a laminating job.Having got the laminating requirements under control you then have to deal with getting release film and breather over a slippery surface and holding it in place while the vac bag goes over the top.As I said in an earlier post,it would be extremely advantageous to have done a trial bagging to seal any leak pints beneath the hull so that the bag works first time.It all seems a bit ambitious for a first timer with keen but inexperienced assistants.

    I have only done a handful of small infusion jobs and I can see that it might well be the way to go.I would be extremely wary about doing a job of this magnitude as a first infusion project.If a couple of hatch lids or smaller panels could be used for practice,that would be a good way to get experience.I'd also be a bit concerned about getting the plumbing layout right for thorough wetting out and perhaps the wastage on the over-run and the flanges.

    I wouldn't think prepreg would be feasible.I have once worked with ambient cure prepreg and it was a special order to get the slow ambient curing resin applied to the fabric.It took a while for it to arrive and it did a very good job-at a considerable cost.The more usual prepreg cures at 120 deg C and few of us can heat an entire boat to that point.It also encourages the moisture content of the wood to leave and that may not be entirely good with resin curing.You can get LTM resins in prepreg that cure at 70 deg C but they cost a fair bit more than the normal blends.Again,you have to heat a good deal of mass while following the recommended temperature gradients and dwell times-not easy.Then there is the point that applying a vacuum will reduce the boiling point of the moisture in the wood and we return to the earlier point about water vapour and epoxy curing....

    My inclination would be to simply wet laminate and apply peelply.You can do a comfortable area and then move to a different part of the boat if the resin starts to cure.If it takes three days to do the boat,so be it.Its a huge amount better than having wet glass slithering around as you try to apply a bag with resin going rubbery.
     
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  10. gonzo
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    gonzo Senior Member

    A single leak is significant. Using inexperienced friends for help make the likelihood of leaks much higher. They are not hard to fix, but someone that understands what is going on has to be on watch.
     
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  11. Howlandwoodworks
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    Howlandwoodworks Member

    Here is my practice run at creating a vacuum seal on one half of my 1:4 scale models hull. By the wrinkles in the plastic and tape you can see it was humbling experience.
    The model is a carvel planked with glued tight seamed and I had some air leakage in the rabbit jointery between the keelson and garboard that was resolved.
    Vacuum infusion for boats is a great develop for small shop hull construction.
    A method of construction that would limit my exposes to neurotoxin is my first mode of operation and I tend to lean towards lower stress strategies. That said vacuum infusion is a very appealing method of construction that the end product is most compatible with the way I intend to used and stored this boat.
    I think the weakest link in this whole process will be the old dog new trick.
    upload_2021-2-1_10-25-13.png
     
    Last edited: Feb 2, 2021
  12. zstine
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    zstine Junior Member

    Hey MY first boat was a Jet 14! Hull 963. I have a junior national championship in that class... back in 1996 i think. Sailed out of Clinton NJ at the time with Charley Engler, Ralph Hanson, etc.
    I do like the idea of vacuum infusion. I'm just nervous I get dry spots. People say you ruin the whole part, though I don't see why you couldn't cut out and repair it. I'm getting a lot of comments about needing helpers and timing issues, but they are all commenting on wet layup, then vacuuming. So that's just making me lean more toward infusion. The great advantage of infusion is that there is no rush... until you start the flow and things don't go as planned!
     
  13. zstine
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    zstine Junior Member

    Well, you and fallguy sure make a good argument for infusion. Sounds like wet layup on this size hull is going to be more trouble timing wise and sorting leaks quick than figuring out how to get infusion right which is all in the prep... And yes, I will certainly practice on smaller parts before attempting the whole hull!
    Thanks!
     
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  14. wet feet
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    wet feet Senior Member

    Good luck with the process.I don't entirely understand the eagerness to abandon all thoughts of just laminating the glass with no vacuum as no other process is as easy for a beginner.A vacuum consolidated laminate is a bit better,are you quite sure it justifies the additional work for your particular boat?
     

  15. zstine
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    zstine Junior Member

    well, this boat is intended to foil. so low weight is important. I intend to use E-glass on the exterior and carbon on the interior.
     
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