Can Fiberglass,Carbon or Kevlar be used w/Mahogany in cold molding?

Discussion in 'Boatbuilding' started by cudashark, Aug 4, 2006.

  1. cudashark
    Joined: Jul 2006
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    cudashark Senior Member

    Dear friends,

    What I mean by this, is, that is there an instance where a fiber(carbon,glass,kevlar) should be used in between the first layer(veneer) and the second layer to strengthen the hull in cold molding.

    Would a wood veneer/fiber/veneer/fiber make a difference.

    Has anyone used such a laminate schedule?

    Of course I am looking for strength, abrasion resistance and impact resistance in the lightest form of cold molding.

    LOA 33', beam 9.6' plaining hull hard chine. Scantlings suggest a minimum hull thickness 0f .62"

    Ray
     
  2. dougfrolich
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    dougfrolich Senior Member

    Use the higher modulus materials further from the neutral axis. i.e. laminate your vaneers then use carbon for your inside skin.
     
  3. jonsailor
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    jonsailor Boat designer/builder

    Yes I totally agree or totally wasted. If you go to the trouble of using a higher modulas skin, then in true theory, you should have a balanced panel properties inside and out so the next step is to think about not using cold moulded??? and have the good skin inner and outer on a lighter core???
     
  4. dougfrolich
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    dougfrolich Senior Member

    I agree! but somtimes there are other concerns--tooling, asthetics,etc...
    Mabey;
    cold mold the core (Cedar-Balsa-Cedar), lay-up the structural skins, add the decrative veneer.
     
  5. cudashark
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    cudashark Senior Member

    Yes the final result would be Mahogany above the waterline with bright work finish. It will be a retro style craft as modern as I can make her.

    My shop which is a cabinet shop and by trade I am a finish carpenter. Cold molding seems to be within my skill sets. Well at lease the wood working aspect.

    So cold molding is the plan. I am also proficient with the vacuum veneering process via custom exterior doors and furniture.

    My original concept was 1/8 mahogany ( keel to gunnels)

    /then some type of re-enforcing fiber (epoxies)/1/8 mahogany at a 45

    / Another re enforcing fiber layer then / mahogany stem to stern

    / with a glass 4-6oz abrasion layer wet out clear with a coat of UV varnish above the water line.

    Painted below the waterline.

    m/f/m/f/m/f is that over kill?
     
  6. Tad
    Joined: Mar 2002
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    Tad Boat Designer

    Cuda,

    Interesting and complex question. Has it been done? Yup,....But was it worth it? That depends.

    I would say there is great potential to waste lots if money and effort for very small structural gains. What is the aim? Do you believe this construction will be lighter, or stiffer, more resistant to impact, or structurally more stable?

    Usually the bottom and topsides of a high-speed planing hull will be different thicknesses, the loads on the bottom are much higher. Usually the framing system (panel size) will also be different in these areas.

    Your inner skin of 1/8" mahogany will need an extensive support frame so reinforcing fabric on the inside is out. So I can see burying the inner reinforcement between the first and second layer of wood. After that I see little gain in adding fabric until you get to the outside. Obviously if the reinforcement is carbon then for aesthetic reasons it would be buried. If you want to use carbon then it must be engineered to take the total load, and the wood becomes cosmetic skin and "core".

    The Gougeon Brothers have done extensive testing on these types of questions and I would really recommend contacting their technical department, even if you are buying epoxy from someone else. I would also recommend building your own test panels, weighing them, and then doing some bending tests (hydraulic jack) and drop impact tests with a weight.

    Finally I would really recommend you call an expert, give Chris Franklin a call 207-563-1186.

    All the best, Tad
     
  7. Eric Sponberg
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    Eric Sponberg Senior Member

    Carbon over Western Red Cedar has been done--Saint Barbara

    My design Saint Barbara, built by Van Dam Woodcraft in Boyne City, Michigan, is built with carbon fiber over western red cedar. See some photos below. The owner wanted wood strip-planked construction, but did not want to deal with the expense and weight of the veneers. So the inside and outside skins over the 3/4" strip planking were a first layer of 90-deg carbon, followed by two layers of +/-45-deg carbon. These were spec'd in accordance with advice from The Gougeon Brothers who relied on their testing of similar such panels. The hull is amazingly rigid and strong.

    Saint Barabara also sports a lifting keel (solid wood blade reinforced with carbon panels inset into the surface), a carbon rudder in a drum, a carbon fiber wingmast and boom, and unique carbon fiber spinnaker poles hydraulically operated from the cockpit. Hydraulics also include the mast, boom and keel operations. The sails are cuben fiber from Quantum Sails in South Africa.

    Saint Barbara will be ready to launch next year (spring 2007) and hopefully will be well received and perform admirably. For a more complete story on the design, it is on my website at: http://www.sponbergyachtdesign.com/SaintBarbara.htm.

    Eric
     

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  8. cudashark
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    cudashark Senior Member

    Thank you Tad,

    I'll call Chris on Monday. I am going to make some test panels. In fact The Ocean Engineering Dept at The Florida Atlantic University has agreed to run a complete characterization of composite laminates such as flexture, tension, compression, interlaminar shear, interlaminar tension, delamination (fracture toughness), and low & high velocity impact tests, etc.

    I have already purchased several yards of different material so off I go. I think Tad you are right in the fact that the savings in weight may be nominal, nothing that couldn’t be handled by 100 hp up grade.

    An undergrad will be summarizing all the data and I’ll make it available to anyone who cares to look. cudashark@adelphia.net.

    Also my hull design should be finished in a week or so and anyone who would like a look at that I’ll make that available in AutoCad…dwg.

    In fact any designers want to critique my work that would be great!



    Mr. Sponberg Saint Barbara is beautiful, is she in St Augustine? I’m in WPB if you are ever around please look me up.

    Ray
     
  9. Eric Sponberg
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    Eric Sponberg Senior Member

    Ray,

    Thanks for the compliments. Saint Barbara is still in the shop at Van Dam Woodcraft in Boyne City, Michigan, awaiting final fitment of the mast, keel, rudder, hydraulics, and electronics. The owner has a summer home on Mackinac Island, and that is where he will be sailing her next year.

    My next intended trip down your way will be for the Ft. Lauderdale Boat Show at the end of October to help show my Moloka'i Strait 75 motoryacht which was launched a few months ago. She is going through final finishing here and in Ft. L.

    Eric
     
  10. BJBarbata
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    BJBarbata New Member

    Carbon fiber woody sandwich?

    I'm building a Glen-L Monte Carlo, which uses cold molding of plywood. I'm intrigued by the possibility of laying down the first layer against the frame out of a nice mahogany, then building up carbon fiber for weight saving, strength and ease of getting around curves, then a top layer of mahogany. Any advice on this?
     
  11. Eric Sponberg
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    Eric Sponberg Senior Member

    BJB--That would be using carbon fiber in the wrong way. Carbon fiber laminates are more than 3 times heavier than mahogany, so you are not saving any weight by switching wood out for carbon fiber. Really good carbon laminates weigh about 92 lbs/cu.ft., whereas mahongany without epoxy on it weighs about 28 lbs/cu.ft. Carbon fiber is also really expensive, and designers and builders tend to use only a minimal amount to most efficient effect--enough to accomplish adding stiffness and strength, but no more. To do that, the carbon fiber should be very thin and go on the very inside and the very outside of a sandwich laminate. Putting it in the middle of the laminate is the wrong place to add carbon fiber. Of course, putting carbon fiber on the outside and inside skins necessarily hides the nice mahogany grain, so that's no good if you want the wood grain to show. In all, it's not a good idea because it won't accomplish your objective.

    I hope that helps.

    Eric
     

  12. dougfrolich
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    dougfrolich Senior Member

    Here is a a portion of a study from a while back--comparing a state of the art pre-preg hull shell panel to a much less expensive, wood-wet lay-up CFRP hull shell panel. I think the wood carbon panel shows a reasonable way to use strip planking and carbon for a light, strong, stiff, hull shell that could be built on a station jig. This example was from a study for a 112 foot sailboat.
     

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