Carbon Kevlar

Discussion in 'Fiberglass and Composite Boat Building' started by m3mm0s rib, Oct 1, 2011.

  1. m3mm0s rib
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    m3mm0s rib Senior Member

    I would like from those who know how to tell me if I want to do my boat kevlar carbon how many layers will be needed and in what order. I put epoxy resin or ethylene-vinyl. Thanks
     
  2. PAR
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    PAR Yacht Designer/Builder

    That question isn't answerable. The laminate schedule for any boat, regardless of materials employed in it, are application specific. In such, only the boat's designer can really answer your questions. If you have a design and want it converted to include a carbon/kevlar laminate, then you'll have to employ a designer or NA to engineer a new laminate schedule that reflects the loads imposed.
     
  3. m3mm0s rib
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    m3mm0s rib Senior Member

    Thanks PAR but i am the designer. I dont know many things about carbon kevlar and i want to learn more
     
  4. PAR
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    PAR Yacht Designer/Builder

    Developing a laminate schedule with these types of materials requires engineering around the advantages and disadvantages of the physical properties of the materials. As a rule carbon/Kevlar composites are highly engineered, so you first step is to research the material choices and learn about their physical properties.
     
  5. tunnels

    tunnels Previous Member

    How can you be a dsigner and have no knowledge of the materials you want to use ?? its one of the first things you need to have is a sound and complete understanding of before puting you finger on the go button !!

    Carbon and Kevlar are at opposite ends of the stretch scale !!
    Carbon has little to no stretch and kevlar has a lots so trying to mix them into a laminate for a boat hull or what ever is absolutely pointless !!! as you will have one material fighting against the other !!.
    You use one or the other but not mixed together unless it is a very special purpose like the layer of Kevlar on the outside skin for abrasion purposes on the bottom of a hull that gets pulled up on a sandy or rocky shore regularly .
    Kevlar was used exstensively in the late 1980s and 1990s but then feel from Grace as Carbon became more popular . its good for white water canoes and Kayaks etc etc where you are pounded into rocks and the like !!
    Personally carbon is pointless unless you are racing or need super light very strong what ever .
    There are no tell tail signs when a carbom laminate has reached it self distruct point !! It just goes bang and its gone !!! So in most situations its dangerous to use !!!
    Glass is some where in between those two !,Glass used with a good quality Vinylester resin and good glass matts and materials its all thats reqiured to build almost any hull /deck or what ever .
     
  6. PAR
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    PAR Yacht Designer/Builder

    Carbon and Kevlar can be used in a laminate (and are used all the time), but again these types of laminates have to be highly engineered or you are just wasting really expensive materials for no appreciable gain.
     
  7. Landlubber
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    Landlubber Senior Member

    from a saved article by Eric Sponberg...read and learn....


    On using carbon fibre
    One of the worst misconceptions of carbon fiber composites is the thought that a little bit of carbon will add a lot of strength. Not so.

    When you engineer a laminate of any sort with materials of different strengths and stiffnesses, you need to take into account two stiffness factors: E = modulus of elasticity of the material (Young's Modulus), and I = moment of inertia of the laminate cross section. The bending and stress behavior depends on the product ExI. If two materials of vastly different stiffness are bonded together in a working structure, in this case say wood and carbon fiber, then an even match and complementary bending behavior will be when the ExI of the wood equals the ExI of the carbon. E of wood can be anywhere from 500,000 psi to 2,000,000 psi, depending on the species of wood. Carbon fiber, on the other hand, can have an E anywhere from about 7,000,000 psi to 14,000,000 psi--many times greater than wood. In a wood rudder, the I of the rudder cross-section can be relatively high because the primary determinant for I is the thickness of the section, raised to the third power. With only a strip of carbon fiber within the laminate, however, the width of the carbon tape is generally not enough and the thickness of the carbon is really, really thin; and while the tape's distance away from the center of the rudder section is important and adds to its I, usually the I for just a strip of carbon is not anywhere near enough to add sufficient strength and stiffness to the section. The I is really, really small.

    So what I am trying to say is that if you are going to add carbon fiber to a rudder, you had better be prepared add a lot of carbon fiber over the whole skin in order to make a significant difference. Stress in the laminate is always going to build up faster in the stiffer material (the one with the higher E) and if you don't have enough material in there to handle the stress that it is going to attract, then you have a potential for a real failure.

    This is exactly what happened to the carbon fiber and aluminum rudder stocks for so many sailboats in the 1979 Fastnet Race disaster. Aluminum rudder stocks were shaved down thinner a bit (to save weight) and reinforced with just a small amount of carbon on the outside. Not enough carbon was there, yet the carbon tried to assume the lion's share of the load because it was stiffer than the aluminum. The carbon fiber failed when it got over-stressed, and once the carbon failed, there wasn't enough aluminum section left to handle the loads, and so the aluminum failed.

    Finally, one of the biggest follies I have seen over the years is when boat builders use narrow strips of carbon fiber tape laid up into the hulls of boats in a cage like pattern. They think that this carbon "cage" will add a lot of strength to the hull, making it very stiff, like an internal framework. Nothing could be further from the truth. Generally, there is not enough carbon in there to do anything at all, the builders are simply throwing away money. If you want to make a really strong carbon fiber hull, then you have to have whole layers of carbon fiber spread throughout the laminate, and on both sides of the core if there is a core.

    Eric
    __________________
    Eric W. Sponberg
    Naval Architect
    St. Augustine, FL
     
    1 person likes this.
  8. m3mm0s rib
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    m3mm0s rib Senior Member

    TUNNELS The vessel which manufacturers are racing and I want to do the best. These materials are not widespread in the general construction because have high price. It makes sense not to know all. Yes I am a designer and manufacturer of the model but that does not say anything. I got the mold and I want to know what is best for me before proceeding in production
     
  9. PAR
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    PAR Yacht Designer/Builder

    You need to hire a designer or NA to spec out a laminate schedule for your design. There's no short cut to this, just lots of calculations, which clearly you haven't the ability to preform yourself. Naturally, you'll have to provide a full set of plans, weight and centers targets, proposed propulsion, tankage allocation, etc.
     
  10. tunnels

    tunnels Previous Member

    And all thats never going to be a end to it all as you then have to find some skilled worker that understand what they are doing to make it all work or you will have the biggest disaster you can imagion on your hands . Oh boy !!:?::(:idea:
     
  11. PAR
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    PAR Yacht Designer/Builder

    It's assumed you'll have skilled composite workers. As a rule, I don't hire plumbers to rewire my house either.
     
  12. m3mm0s rib
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    m3mm0s rib Senior Member

    Maybe we are not naval architect BUT CERTAINLY NOT WE confectioners
     
  13. Stumble
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    Stumble Senior Member

    M3mm,

    No one is criticizing you for not being NA's, but what you are asking for just isn't possible. A good laminate schedule can take a huge percentage of weight out of a boat by using what needs to be there, and leaving behind what doesn't. But this is a very complicated calculation dependent on a huge number of variables.

    If this is a race boat, the speed the boat will travel at max speed, wave conditions, wind conditions, impact resistance, shape, power, power location, transmission type, fuel load, personal load, expected life span, ect... All play a part in determining how think each section needs to be to survive the loads it will encounter. The keel for instance might need more thickness than the gunnels, if the boats are high performance enough that life expectancy isn't an issue, then you might be able to shave off another 5% of weight...

    All this adds up into a huge amount of number crunching, and it really isn't possible to do yourself. At least not unless you are a NA in which case this is moot. The other option is to hire a designer for a few thousand dollars to do the work for you, which compared to the cost of a CF boat is peanuts.
     
  14. michael pierzga
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    michael pierzga Senior Member

    Many times your supplier of composite materials can also, for a small fee ,re engineer your calculations for a conventional glass laminate into a more exotic schedule. Its best to communicate with your supplier .

    Be careful with carbon...it is expensive and worthless unless the structure is engineered for it.
     

  15. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    There's an idea, let the "gifted" counter guy at Wholesale Fiberglass, do your laminate schedule. <removed>

    .
     
    Last edited by a moderator: Oct 5, 2011
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