Carbon epoxy tender

Discussion in 'Boatbuilding' started by Sygeor, Nov 29, 2016.

  1. Sygeor
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    Sygeor Junior Member

    Hi to all,

    Nowadays i start a new project about a 2,40m rib tender.
    I have made the mold (hull & deck) and my first thought is to build it from epoxy and carbon materials than polyester and csm fibres.

    In the past, the tender were set up from :

    1. 1 layer 450 csm matt
    2. 1 layer woven 600
    3. 1 layer 450 csm matt
    4. Simply polyester resin

    This time my thought is the epoxy version of it.

    My questions are :

    1. How many layers and what carbon fibre is better to use for this situation ?
    2. It's better to put between the layers core material (like soric xf or coremat) or not.

    Of course i know that an exact answer need naval architect but i want to know for the beginning your eperience.

    Thanks for your time

    George
     
  2. TANSL
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    TANSL Senior Member

    In such a small boat, with such a small thickness, the weight savings you are going to get will be very little while the price will increase.
    What do you intend to achieve by using sandwich-type lamination?.
     
  3. Sygeor
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    Sygeor Junior Member

    Thanks Tansl for the reply,

    The only carbon fibres choice will reduce the thickness about 2mm. Will be good or have problems in stiffness ?

    Thanks

    Regards

    George
     
  4. TANSL
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    TANSL Senior Member

    Keep in mind that the strength of a laminate does not have to be proportional to its thickness. The resistance depends on the fiber content of the laminate. So you would have to analyze the carbon fiber you want to use and compare it to the fiberglass laminate you put in your # 1 post.
    The thickness of the dry fiber of your fiberglass laminate (post #1) is 3.5 mm. Therefore, a reduction of 2 mm in thickness does not seem possible. In any case, the total thickness which, as I say, is not the most important, could be reduced by placing less resin, for example, by infusion. This way you would reduce the thickness and the weight without changing the resistance of the whole.
     
  5. jorgepease
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    jorgepease Senior Member

    I would think a thicker foam with less uptake of resin (corecell or any pvc cheaper foam) and much less glass will give you a very light and stiff tender.
     
  6. Sygeor
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    Sygeor Junior Member

    Last month i build a 10m rib two times, one with hand lay up and one with vacuum infusion.

    In the first case the thickness of the laminate is 1cm and in the second about 5mm, almost half.
    The units of the laminate is about 5400 and contain csm and triaxial fibres.
    The stifness of the laminate in second version isn't good than the first.

    Your thought

    Thanks
     
  7. TANSL
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    TANSL Senior Member

    If we put the same layers of fiberglass in a handmade laminate or another made by infusion, the resistance of the assembly should be practically the same. The resin contributes somewhat, but very little, to the final strength, but greatly increases the weight of the whole. So with any construction procedure we must try to put the necessary resin, but not another gram. With the infusion procedure, if performed well, it is more easily achieved that the amount of resin supplied is exactly what is needed.
    The two boats that you have built, if they have the same laminate scheme, should have the same resistance.
    For example, ISO 12215, which is used for the scantling of recreational craft, in calculating the required strength of the laminates, does not take into account the resistance provided by the resin.
     
  8. Sygeor
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    Sygeor Junior Member

    Thanks TANSL for the infos.

    I agree with your last post but i'm afraid the 5mm thickness of the laminate.....the stress cracks, the damage in a wild sea. of course i'll set up stringers in the hull.

    Your thoughts ?

    George
     
  9. TANSL
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    TANSL Senior Member

    A laminate scheme consisting of 1 layer 450 csm matt + 1 layer woven 600 + 1 layer 450 csm matt, is very flimsy, whatever its use. But, I repeat, do not be fooled by a thickness of 5 mm. If the content of the 5 mm is mainly resin, it will be very weak and fragile.
    I think you should put some fabric.
    Of course, increasing the number of reinforcements decreases the panel surface and therefore allows a thinner panel, but may not be sufficient if the fiber content of the panel is not enough. The reinforcements, with the panels, form a set and as such must be studied.
    If you give me some data on your structure, I could do some calculations to check up to what thicknesses could be reached.
     
  10. Sygeor
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    Sygeor Junior Member

    I have about 5300 fiber units :

    1x csm 23 matt
    1x csm 225 matt
    2x csm 450 matt
    1x triaxial 900
    4x csm 450 matt
    1x triaxial 900
    2x csm 450 matt

    Infusion resin
    Vacuum infusion method (95%)

    thickness 5mm (big areas) & 10mm (keel & transom)

    This infos are for vacuum infusion and not hand lay up

    What is your opinion about the fibre structure ?

    Regards

    George
     
  11. TANSL
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    TANSL Senior Member

    I can only speak of generalities. The distribution of the stresses through the thickness has a linear shape, the highest values in the area away from the neutral axis and value cero at the neutral axis. From that point of view, it is not advisable to put fabrics in the center of the laminate, but on the contrary, towards the outside, away from the neutral fiber, where stresses are bigger. On the other hand, since the stress distribution should be more or less symmetrical with respect to the neutral axis, the layers should also be symmetrical with respect to the neutral axis.
    In practice, this is not easy to achieve, but it should be tried.
     

  12. Sygeor
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    Sygeor Junior Member

    Very usefull infos TANSL.

    Thanks for helping
     
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