Need "help" to understand

Discussion in 'Boat Design' started by longcours62, Jan 1, 2014.

  1. longcours62
    Joined: Jul 2011
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    longcours62 Junior Member

    One part of the book "Principles of Yacht Design"
    Because with my poor English level I understood the Fig 11.23 and the text "Wet laminates" (pages 232 and 233 of the first edition).

    Concert the loss of of strength and modulus for wet laminate.
    But another French guy (with far better level in English than me) said this text and fig are for the loss of strength due by "osmosis" .

    But in this text the author wrote :

    "One thing to remember though, is that, if you store the boat on land during winter and let the laminates dry out, the process effectively start from year 0 when you relaunch the boat again" and it is why I understand the authors ask about "wet " and not "osmosis" Because stay ashore one winter never "repare" an osmosis" problem (not remove the blistering and the "acid" from the hull .

    But after the answer of the another French guy , I began thinking : my English comprehension could be worst than I am thinking !! Not possible .... euh may be ?:D:confused:
     

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  2. upchurchmr
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    upchurchmr Senior Member

    All typical matrix materials absorb water (by osmosis) from the environment starting from the time they cure. I am familiar with aircraft usage. In air, the final percentage of water in the laminate depends upon the relative humidity of the environment and the length of time. If the laminate reaches "saturation" - the max water in the laminate for that humidity in the air - then the laminate water stops increasing. If the humidity in the air decreases, the percentage of water in the laminate decreases until it reaches equilibrium.

    If you take a boat out of the water you have less water in contact with the laminate. The laminate will immediately begin to dry out until it reaches equilibrium with the atmosphere - but this takes a long time to reach the final percentage of water in the laminate.

    Does your text say how the strength curves were tested? Was the sample submerged in water or just one side like a boat? Did they actually test to 100 years or is this a theoretical calculation?

    Actual physical damage like a blister will never reverse.
    I don't deal with polyester and don't understand the "acid" comment.

    Hopefully some of the NAs on the forum can explain specifics for polyester.

    A second language is tough, I know from my failure with Japanese. Keep trying and good luck.
     
  3. Petros
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    Petros Senior Member

    this is a simple concept, the chart shows the longer a polyester/fiberglass hull is in the water, the more strength it will loose over time.

    And the author pointed out that the time the hull is stored out of the water will delay the strength loss.

    Is there something about that you do not understand? what are you confused about?

    The reason is not so important as much as you understand that it happens. I am not sure "osmosis" is the right word but perhaps moisture infusion is more accurate. It does not matter, polyester and fiberglass hulls get weaker over time when in the water.
     
  4. jehardiman
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    jehardiman Senior Member

    "Osmosis" is the term for the ability of a fluid to pass through a membrane (like a single layer of GRP). Fluid will diffuse into the GRP until it reaches equlibrium. Remove the fluid and it will diffuse out of the GRP. You are correct that any damage (generally chemical) caused by this osmotic diffusion in/out of the GRP is irreversible, but removing the GRP from the water slows the damage.

    You may be confused by the text using the term "osmosis" to refer to the damage caused by osmosis (i.e. "blisters"), which really describes the chemical damage, not the actual physical process.
     
  5. SamSam
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    SamSam Senior Member

    You're reading more into the text than is there, or at least in the text shown. It says nothing about damage, it says nothing about blisters or chemical acids. All it says is that if laminates become 'wet', they temporarily become more flexible and temporarily lose 'strength' of some sort, I guess probably compressive, tensile, shear and all those type of strengths. When they dry out, they're back to full strength. Like a piece of paper, or dried clay that gets wet, turns to mud and then dries out again.

    IF the 'wetness' causes blistering and chemical acids, THEN you have permanent damage.

    Looking at the graphs, I find it kind of odd that after a year in water, iso resin has gained stiffness but lost strength, while after 0.1 year in water, ortho resin has lost stiffness but gained strength. What's up with that?
     
  6. longcours62
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    longcours62 Junior Member

    Thanks to all

    Because like you wrote I understand "more wet" is the laminate less is his resistance .
    But I let school before 16 years old ...
    And a man on a French forum ( he is in engineers school) said to me I misunderstand, I don't must understand "wet" (as I and you !!) understand but "blister"(or the chemical damage du by water) and absolutely not the "wet" .
    Thanks to all of you , I feel now less stupid whit my poor level in English :p:p
     
  7. JLIMA
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    JLIMA crazed throttleman

    Je parle français, que j'étais un traducteur navale au goverment nous alors que j'étais enrôlé peut-être je peux vous aider?
     
  8. JLIMA
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    JLIMA crazed throttleman

    je peux ne pas être sur mais à honoraires libres message privé moi
     
  9. JLIMA
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    JLIMA crazed throttleman

    since he seems to be troubled by English in his text maybe i can help him in french if any one wants to know what i said feel free to ask I have no intention of offending anyone just trying to help
     
  10. upchurchmr
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    upchurchmr Senior Member

    Hopefully no one is going to be offended with you supplying help.
    I'll call on you if I need help with French - cause the only thing I know is French fries!
     

  11. longcours62
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    longcours62 Junior Member

    What !?


    I am sure your French is better than you said !!
    You know Bordeaux ,Cognac, Champagne and sure you heard few time the word "grève"
    (strike in English):p:p
     
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