Infusion Plan

Discussion in 'Fiberglass and Composite Boat Building' started by jorgepease, Jun 4, 2012.

  1. jorgepease
    Joined: Feb 2012
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    jorgepease Senior Member

    Very complex stuff :)

    For example if I made a symmetrical sandwich "grid" of core strips, say 2" wide by 1 7/8" thick that should yield a pretty stiff grid that could span a long distance distance and if you had good balance you could walk across it.

    Then I laid on top of that a 5/8 sandwich panel and infused them together that would give increased stiffness in all directions or so it would seem to my wood raised brain LOL!!

    Maybe I should make a sample to put it to rest once and for all ... but as you say you have to do the numbers.
     
  2. petereng
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    petereng Senior Member

    Logic and engineering numbers sometimes don't agree. Your logical is fine but it may be "better" both ways. With a grillage its a chicken and egg problem... do I make the skin just good enough to keep the water out then the skin loads are transfered to the grillage (this could be a optimal light condition because the hull surface area is the biggest area and hence the heaviest) . Or do I make a sandwich which is a monoque? (Traditionally this is impossible to cal;culate by hand but a grillage is easy to do by hand. But I use FEA so can model the monoque no probelm) Traditional boat design makes the skins and the grillage of equal import as a safety factor. Ie if the panel breaks the grillage is there to hold everything together. If you go 100% sandwich if it fails it may zipper through the structure and the boat will sink. These things are all calculatable and I do this sort of thing mainly for commercial vessels that need the numbers done to pass survey.

    The grillage approach is also a hang over form where the frames are not only structural but serve as a constrution aid (timber and metal construction), once you are moulding a boat the frames (or bulkheads) don't need to be there anymore except for flooding control . You could build an optimal sandwich in which the outer and inner skins remain the same yet the core is optimise in thickness and density over he entire hull. Cheers Peter S
     
  3. jorgepease
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    jorgepease Senior Member

    I was thinking more for the deck, I wont be the guy wandering too far off the beaten path on the hull :)

    But I just figured out the materials and its not much of a savings over just using solid core and all that extra work definitely a bad idea!
     
  4. jorgepease
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    jorgepease Senior Member

    Believe it or not, I am finally ready to infuse the inside. I was stumped by a leak I could not locate. I finally broke down and purchased an ultrasonic detector and discovered a leak in the core.

    I could hear the hiss but it was not leaking straight through, I finally ended up bogging an area around some holes I drilled nearest to the sound and that was it. I now have a perfect bag and everything looks great.

    My destroyed pump I gave to a vacuum pump rebuilder and in exchange he rebuilt my other pump for free. All I need is a video camera now and I am good to go. Learning a lot of lessons here LOL!!!
     
  5. Tungsten
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    Tungsten Senior Member

    good to hear Jorge,i was wondering what was goin on.
    what kind/brand leak detector did u get?also how accurate was it,did it point you to the exact spot?
     
  6. jorgepease
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    jorgepease Senior Member

    I got the AccuTrak VPE, runs about $300 and change. It's very accurate but It's the first time I use one so don't know how much better those thousand dollar machines are. I think if you can get your shop quiet and don't need to look for sounds in a different band, this machine is just as good.

    This one amplified the noisy pump when I was around it making it tough so I ended up pulling the vacuum and turning off the pump then donning the detector. Also I had to kill the lights, fluorescents, it does not work well around them at all.

    On pinholes in the bag it gets you to the exact spot. Sliding a finger lightly over the area to interrupt the airflow confirms that its a leak in the bag and not from the other side, that is how sensitive it is. A leak is loud, sounds like a jet :) but I was not able to stand 5 feet away and just point the thing around, I had to pass it slowly around the hole boat.

    The nightmare leak I just fixed, I detected a spot where the air flow must have been constrained in the core but it was not the actual spot where air was entering. I had to epoxy an area around some drilled holes a couple of feet away to get that leak sealed and the detector could not hear that actual spot, I think it was too free flowing.

    I was also able to detect leaks where my tubing connected to barb fittings on the pump, even with hose clamps, it was leaking. A little tape fixed that, I feel much more confident with this tool, definitely worth the money.
     
  7. groper
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    groper Senior Member

    wow, thats surprising considering you had multiple layers of glass on the other side of the core, you would have thought it *couldnt* leak???

    All my hose connections, i use tacky tape in or around them and forget the hose clamps...

    Hope it goes well for ya this time...
     
  8. jorgepease
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    jorgepease Senior Member

    Thanks, I think it will go fine.

    I may not be understanding how the leak is happening. I look at it and it doesn't look possible either.
     
  9. SamSam
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    SamSam Senior Member

    Go back to post #140 and it's not hard to imagine at all that there were leaks through the other side.
    It's good to hear about the project again. I don't remember what the plan was, do the hull and then the stringers or do it all at once?
    Good luck to ya!
     
  10. petereng
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    petereng Senior Member

    Hi Jorge, its always best to vacuum check a "temporary" or "constructiuon" mould before you stack it. Just put a breather or some old cloth over it and bag it then you know it will work when you stack it proper, make the bag aiotle bigget thenm the real one and you can reuse it. I stumbled a while without a leak detector but they are a must!! Good luck. Peter S
     
  11. jorgepease
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    jorgepease Senior Member

    Yeah, I am sure that has something to do with it, though its not leaking anywhere else! Thank God!!! :)

    That is a good idea now that I have the larger bag material I can do that. Before I was taping the bag together and that would have been a bear!!
     
  12. jorgepease
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    jorgepease Senior Member

    Just to let everyone know - I infused today and it seems to have worked. You learn something new each time.

    This time I believe I should have opened the valves to the farthest sections of the boat first. It makes a difference but it did not hurt us.

    We had some air bubbles, two tiny spots, that we could quickly plug and then some more that we could not find the source and that was not much ... also by the time we left it looked like they were going to be sucked out ... I left the pump running and will shut her off tomorrow morning.

    Here is a link to the last vid I shot, it does not show the actual infusion just the end, I will post some earlier vides to show that but I ran out of money and could not buy the video camera so just used my phone. Anyway I was too nervous to concentrate on video lol!!

    http://www.youtube.com/watch?v=IirvDHXyiC8&feature=youtube_gdata_player
     
  13. petereng
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    petereng Senior Member

    Congrats Jorge!! with epoxy if you have a dry spot it means that there isn't vacuum there. Get a syringe and needle. Connect the syringe to vacuum and wrap a small piece of tacky tape around the needle. Introduce the needle to the dry spot and seal the needle to the bag with the tacky tape. This will create a better vacuum at the dry spot and it will fill in. Once filled extract the needle leaving the tacky tape to seal the spot.

    If its a leak the dry spot will get worse. When you video move pan slowly please!! and keep in focus!! Well done. Peter s
     
  14. jorgepease
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    jorgepease Senior Member

    Thanks Peter, I was so nervous I could not keep the camera still, sorry. I was hoping I could have bought a camera and just let it run the whole time.

    By the time I left the spot had filled up almost completely, this is strange, the spot was close to the input of resin, it should have been the first to fill up??

    I also had my still camera set up and took a pic every few minutes so those may show better than the video. The majority of the boat had infused in 15 minutes and by 30 I would say that it was infused right up to the mti hose
     

  15. petereng
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    petereng Senior Member

    Hi Jorge, The spot cound be from many reasons and you will never know which one it is, its now history. The spot will fill up if you have very good vacuum. A normal single stage oil vac pump pulls 99.9% vacuum so if your dry spot was say 1litre it will fill to 999ml before it stopped. It stops here because the 1000ml of "air/vacuum" has been expanded and now shrinks back into the void (if this makes sense) If you use a two stage pump then the vacuum is 99.99% or better. If you use polyester or vinylester resin this does not happen as the styrene flashes off and fills the void partially. Thats one reason I like epoxy, no solvents in the resin to fill up bags/voids with. This is a strong reason to never change the pressure level of the bag, pull as deep a vac as you can then leave it at that. If you back the bag pressure off the bag volume changes and your voids will never fill in. I have an absolute vacuum gauge and its very very sensitive. A job like yours may take 2 hours to pull down to its ultimate pressure. This is becuase there is lots of water vapour and various things in the bag and consumables outgas that take a long time to get through the materials and out to the pump. Typical job bottom pressures are 100-200Pa absolute. This can't be seen or measured by mechanical gauges. It takes a second for the absolute guage to respond to something that takes an hour to see it on the mechanical guage. Cheers Peter S
     
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