1. nevilleh
    Joined: Sep 2008
    Posts: 73
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    Location: scotland

    nevilleh Junior Member

    Hi All,

    On our 10 metre vessels (20 knot work / fishing boat) we use a simple csm / woven roving layup.

    I have been advised to change to biax. However our designer has advised against it.

    Lloyds will accept it if i change the woven for biax however Im still a bit worried as the designer has not approved it.

    I think as he is old school he maybe does not have experience of biax (i dont).

    The shell layup is 5 oz csm then two sandwiches of 2oz csm / 2 oz woven / 2 oz csm giving a total of 17 oz.

    Can anyone comment by experience?

    I dont really want to have to change our designer but then I dont want to make a change myself to a material less appropriate.

    Thanks. Neville
     
  2. waikikin
    Joined: Jan 2006
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    Location: Australia

    waikikin Senior Member

    Hi Neville, maybe quote your fabric weights in GSM grams per square meter & make some test panels to see how the thickness/ stiffness compares with the two laminates, it may be that you must put some extra chop in the center of laminate to get comparable thickness. Some 40' gameboats I worked on(fit out & warranty) had the laminate modified to biax & exibited quite some panel flex to my mind- I never actually worked out the ratio across the panels though, also the new laminate included T section stiffeners with uni cap where the previous model had trapeziod/top hat style which may also have increased the actual "span" of the panels. Ask your designer the reasoning behind his recomendations- you've trusted him with the design so far to invest in tooling etc & been satisfied so far I assume. All the best in your endeavours from Jeff.
     
  3. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    If you're using polyester resin, then biax is just a waste of money, but if using vinylester, then biax is a good way to reduce laminate weight and thickness, for the same stiffness and strength.
     
  4. tunnels

    tunnels Previous Member

    Biax is stiched so i would advise against using it for a work boat !!
    Work boats get the kind of abuse and hammering on a day to day basis most glass boat owners can only have night mares about . The layers of glass are tied together by stitching and the resin used and this is a weak point for work boats .A good bash in the side and could part the layers where its stitched if the resin is not strong enough .
    Shear is much lower than with woven . Dont believe me make a test panels and tear them apart and see where it comes apart the easyest !! Always the stitching layer gives way first ,In saying this you are better to use a better resin system . Having done the polyester thing for years then switching to Vinylester it sure is better and stronger and do a sample with the two resins to compear BETWEEN THE TWO . MAKE SAMPLES ABOUT A FOOT SQUARE WITH THE BIAXL GLASS AND WOVEN AND THE TWO DIFFERANT RESINS . BE consistant with your testing so you get a better idea whats good and what not so good ;)

    Are you sure about these glass weights ???
    The shell layup is 5 oz csm then two sandwiches of 2oz csm / 2 oz woven / 2 oz csm giving a total of 17 oz. ?????????

    2 oz csm and 2 oz woven then 2 oz csm again ???????????? That weight i would use in 6 foot dinghy !!
     
  5. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Biax is stitched with a light cotton thread. It's sole purpose it to hold the uni dia layers in reasonable alignment until the goo cures. It has no structural value. It's also important to have good fiber/resin ratios, which aren't typical in hand layups using polyester or vinylester resins. If failures, between stitched biax layers is noticed, then you resin/fiber ratio is way off. This isn't the fault of the fabric, but the application, laminator or both. I too have a huge issue with the posted schedule.
     
  6. dougfrolich
    Joined: Nov 2002
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    Location: San Francisco

    dougfrolich Senior Member

    it's got to be 24oz WR Ive never seen 2oz Woven Roving
     
  7. tunnels

    tunnels Previous Member

    Lightest ive seem is what my son uses for his model aircraft!!
    fine woven acts like peel ply ! :eek:
    If its buried in a laminate its the weak point and thats where it peels from :confused:! Unless you use epoxy resin that has the strength to hold its self together . :)
     
  8. waikikin
    Joined: Jan 2006
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    Location: Australia

    waikikin Senior Member

    Likely to be 18oz woven
     
  9. Landlubber
    Joined: Jun 2007
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    Location: Brisbane

    Landlubber Senior Member

    ...nup, just got to be 24 oz..... I read this earlier, and though WTF, so clicked off, I guess we should respond when we see something that appears to be obviously wrong, someone just might read it and copy...Chinese R&D...research and duplicate....
     
  10. tunnels

    tunnels Previous Member

    18 OZ is the most commonly used size any way !! 24 oz is pretty heavy , i havent seen 36 oz for many years !!:D
     
  11. waikikin
    Joined: Jan 2006
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    Location: Australia

    waikikin Senior Member

    18 oz per sq yard comes out at 2 oz per sq foot thinks I for a logical conversion/explanation of Nevilles post, but I like to use metric for my work. Regards from Jeff.

    http://designer-entrepreneurs.com/blog/illustrations/gsm_to_oz_yd_2.pdf
     
  12. tunnels

    tunnels Previous Member

    The joys of life !!I never heard of that before !!
    1 Sqr foot weight :eek:
    In all my 35 years theres always something to learn !!Something new when you think you have seen it all .:?:
     
  13. waikikin
    Joined: Jan 2006
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    Location: Australia

    waikikin Senior Member

    Hi Tunnels, Same here, Just thinkin' out loud, 'cos thats how imperial choppy weight is measured,"The shell layup is 5 oz csm then two sandwiches of 2oz csm / 2 oz woven / 2 oz csm giving a total of 17 oz."........ per square foot, looks like he's keeping the units2 consistant like with metric fabric weights, mebee Nev can tell us what he meant:!: All the best from Jeff.
     
  14. nevilleh
    Joined: Sep 2008
    Posts: 73
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    Location: scotland

    nevilleh Junior Member

    Sorry Ive misled you all. We are metric over here in the uk, but some laminators still use the older sq ft weight terminology.

    To keep it all metric we use 1500 gms / sqm csm , then two sandwiches of 600 gms csm/600 gms woven/600 gms csm which gives a total of 5100 gms / sq m.

    The smaller shear strength of biax worries me, and yes we have done extensive research on the shear with our traditional layup which was the reason for us to move to wax free resin a while ago.

    Still wories me even with wax free resin the fact you can hammer a wedge in and split the layers.

    Outside using epoxy it seems that we may not be able to keep the strength and lessen the weight.
     

  15. Landlubber
    Joined: Jun 2007
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    Location: Brisbane

    Landlubber Senior Member

    "Still wories me even with wax free resin the fact you can hammer a wedge in and split the layers."....you are laminating........whats with this wax free bit, surely you were not using waxed resin during lamination......tell me I have read this wrong.
     
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