Extra buoyance

Discussion in 'Sailboats' started by BertKu, Jul 8, 2016.

  1. BertKu
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    BertKu Senior Member

    Yes PAR, I will do so. Bert
     
  2. BertKu
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    BertKu Senior Member

    Thanks PAR, I hope it is the closed cell one. Bert
     
  3. Steve W
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    Steve W Senior Member

    Par, could you share the foams that actually do work. I have not yet found any but would sure like to do some immersion tests because if it does exist it is the best solution. In my experience all foams regardless of wether they are closed cell or not are made up of some sort of resin, polyurethane for most pour foams I have encounted, and air bubbles. once the skin is compromised a lot of those air bubbles are free to take up water and they do. Last summer we dug out over 100lbs of waterlogged foam from under the vee berth of my sons boat, a boat I designed and built and launched in 1987 and I know it was supposed to be closed cell. It was our own fault that it got wet as water comes in from the articulating retractable sprit if we stuff the bow and we had never got around to tabbing in the berth top which would have prevented it getting to the pour foam. I have generally had better luck with Styrofoam blocks resisting water intrusion but I have seen that waterlogged too. As I say, I would love to find an A/B foam that truly does not absorb water that I can prove to myself in real world immersion tests so if anyone can lead me there I will buy some and test.
     
  4. gggGuest
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    gggGuest ...

    Don't believe there's any such thing, but some do absorb a lot less than others.
     
  5. PAR
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    PAR Yacht Designer/Builder

    Well I guess it depends on what you find acceptable. Epoxy will permit up to 3% moisture ingress, but is considered waterproof. I often use epoxy to seal questionable foam. A few percent moisture absorption is essentially waterproof.
     
  6. Steve W
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    Steve W Senior Member

    Ok, where can I buy an A/B pour foam that has only a few percent moisture absorption?
     
  7. PAR
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    PAR Yacht Designer/Builder

    I've used a number of different foams, but the stuff from US Composites is a frequent supplier. The thing with these foams is they're not designed to be continuously immersed. They are closed cell, but they're not perfect and have pin holes in a certain percentage of these cells, so continuous emersion will cause significant absorption over time.

    If used as designed, such as a floatation chamber or other application where it's encased and essentially dry, you're fine. Assuming some damage causes a leak, no problem, if you get to repairs relatively quickly. If you don't, over years it will wick from pressurized cell to cell. This is one reason I epoxy coat it.

    Very often I wetout a soon to be foam filled compartment, and before the epoxy has kicked off, I pour the foam, which expands against the wet goo. Both eventually cure, are sealed and also married to each other. In other applications I'll use a plastic bag, visqueen or other protection. I haven't tested it yet, but it was suggested I try that "FlexShot" rubber in a can product seen on TV, to protect the foam.

    For it's role, it works well, assuming you get after any breaches fairly quickly.
     
  8. Stumble
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    Stumble Senior Member

    I actually like the idea of putting a heavy trash bag into the compartment first then poring the foam into that. It should flow to fill the gaps, but still be easy to remove if you need to, and of course the bag would help in the removal process. I would be tempted to use multiple smaller pours instead of one large one but I'm not sure it's critical.
     
  9. BertKu
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    BertKu Senior Member

    Hi PAR, Yes it is a South African product. I have not been able to extract the manufacturer’s name from this supplier.
    What I have done is, to weigh a clean dry empty plastic 2 liter Coke bottle. The weight is 49 gram. Hereafter I have filled it with 2 parts foam. Tomorrow I simulate a cut in the hull or in my case my extension. I will cut deep in the foam . Then submerse the large cut bottle, completely immerged in water. I will leave it for 1 week and 1 month. After drying the outside of the bottle, I will measure it again. Then it should be less than 1% more weight. (Hopeful) Bert
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    Interesting suggestion, could help keep moisture from infiltrating the form as well.
     
  11. PAR
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    PAR Yacht Designer/Builder

    Bert, though the test can be helpful for comparative reasons, it is using the foam in a non-recommended way. These foams aren't intended to remain submerged, but to act as temporary flotation in case of a breach. This is one of those areas we could use some data on all the major formulations, from the typical suppliers.
     
  12. BertKu
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    BertKu Senior Member

    Thanks PAR, I am aware not to use it in permanent submersion. However, I will, like the person who sold me the hull, never know when there is a small leak and slowly the foam start absorbing more and more water. In my case I would not know whether I have a leak in the extensions. Except if I check the weight all the time.
    But I do agree with your point. Thanks, will still see what the submersion does in a month time.
    Bert
     
  13. PAR
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    PAR Yacht Designer/Builder

    When I put this stuff in a compartment, it's never a fully sealed compartment. It has (often quite small) ventilation holes top and bottom so air can circulate. In the event of a leak, the holes will weep, but the volume of foam inside, prevents gaining very much moisture gain (initially). I don't think any compartment should be solidly sealed, filled or not. I can think of no building material or type that makes this a tolerable acceptance. So, with ventilation holes, even a small pinhole leak will eventually cause some moisture to drain out, suggesting further investigation.

    I've been doing this for a number of decades and started when I saw a popular daysailer with twin chambers, running down each side of the boat. They too had small vents, but had become plugged (sloppy repairs) and the hull sides would bulge out several inches in the hot sun, from the captured air expanding inside them, eventually fracturing some laminate. I vowed to never design or build something that could cause this.
     
  14. phillysailor
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    phillysailor Junior Member

    I used exercise balls from a local "5 and Below" store. Cheap, thickish rubber, expanded them in place. Years of service so far. Also strapped buoyancy bags under the gunnels: used commercial (Holt) product b/c it was visible and they had the loops to position retention straps. Also years of service.
     

  15. BertKu
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    BertKu Senior Member

    That is interesting. I was testing the wine bags of 5 liter, but your solution is a better one. Will check the same kind of store here in town. We call it the 5 Rand place (35 USA dollar cent) Bert
     
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