Beach Sand or Earth Mold for Ferrocement Steel Fiber Reinforced Concrete Boat Yrvind Design

Discussion in 'Fiberglass and Composite Boat Building' started by mustafaumu sarac, Dec 13, 2017.

  1. mustafaumu sarac
    Joined: May 2017
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    mustafaumu sarac Senior Member

    I have a yrvind design drawing of a 120 x 420 x 90 cms boat , fully closed. I want to build it with ferrocement but my idea is more modern , I will not use chicken wire but 1 inches long steel fibers in concrete.

    I thought if I dig out beach sand and make a female mold , I could lay my sfrc concrete inside.And I know old timers used that technique.

    I am thinking to lay nylon sheet inside of mold because sand could be deformed by wet concrete.

    Thinking loud , I think I must use 2 or 3 layer of chicken wire to stabilize the concrete on plastic sheet.

    What do you advise ?

    mustafa umut sarac
    istanbul
     
  2. rwatson
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    rwatson Senior Member

    In a kindly way, I advise you not to create another wreck to litter the beaches of the earth.
    Seriously , you have no idea what you are doing. You could barely build a house with the concept, and many have tried.

    Stop now.

    Ferrocement boats that actually work are a LOT more complex, and are a lot more involved than you obviously think.
     
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  3. mustafaumu sarac
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    mustafaumu sarac Senior Member

    I think you saw an engineering article with lots of equations and this made you think that way.

    Lets put another way , you went to mit and now living in tasmania with lots of equations in your mind , dont stop , share your deep tasmanian knowledge...

    cmon.....
     
  4. gonzo
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    gonzo Senior Member

    You will have no control over the thickness of the hull, which will be critical in a boat that small. Short steel fibers will not provide the tensile strength necessary for reinforced cement. There is nothing modern about your idea, simply a lack of understanding about the material and construction techniques. There is a huge amount of information online about ferrocement. It has been around for a couple of centuries and was first used in a boat.
     
  5. mustafaumu sarac
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    mustafaumu sarac Senior Member

    It has been around for couple of thousands years and its been invented by romans - some say great pyramid stones were casted insitu- By the way I am writing from capital of Roman Empire . You are handwaving. Thickness control is easy and steel fibers are excellent for tensile strenght. It depends how much you add and % 8 by weight is industry standard but I will mix faraway more. And I am thinking to mix UHPC or Reactive Concrete.
     
  6. gonzo
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    gonzo Senior Member

    Reinforced concrete is a French invention. It was by Joseph Monier in 1869. By the way, try not to be insulting. It doesn't matter what location you are writing from if what you say is wrong.
     
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  7. Barry
    Joined: Mar 2002
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    Barry Senior Member

    Concrete is relative strong in compression (though normally a concrete pillar will fail due to shear)
    It has extremely poor tensile strength and hence the need to add in a rebar or long steel fibers to take the tensile load. Generally the steel rebar/fibres using your words should run in the direction of the anticipated tensile loads. If you throw in 1 inch long fibres that have random direction it is unlikely that you would gain the strength desired as compared to a
    symmetrical mesh that has say half of the steel running in the longitudinal direction along the hull. In order for the steel to take a load, it must offer adhesion between the steel and the concrete. I would doubt that 1 inch smooth fibres would suffice. The bumps on normal rebar provide a mechanical joint, if you will.
    If in your random throwing in of your 1 inch fibres, there is a void in the fibres or all the fibres are aligned say vertical to the length of the hull, there will not be any ability of the fibres to carry the tensile loads in the longitudinal direction and this then this load would have to be taken by the concrete. (which is said is a poor material for tension)
    A strong steel mesh would be the way to go. It mechanically is attached to the concrete due to its shape and provide a continuous load bearing fibres ( not that there are fibres in steel) to
    carry the tensile load.

    Concrete compressive strength 20 - 40 mpa 3000 to 6000 psi
    Concrete tensile strength 2 - 5 mpa 300 to 700 psi
    Mild steel tensile strength 400 - 500 mpa 58,000 to 72,000 psi

    Just an example
     
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  8. rwatson
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    rwatson Senior Member


    OK, we have a bright eyed amateur here again.

    You, my good man, are talking to someone who has actually built and sailed boats, has worked on ferro-cement boats over 35 feet, and personally investigated dozens of failed, falling apart big boat projects.

    The fact that you are talking about wire as a structural element reveals how little you know about the technology. Wire is useless, because it is smooth and pulls out of concrete. Even "chicken mesh " has to be applied in 3-4 layers, and tied together every 6 inches, on a much more robust steel armature.

    The other point is that this concrete, steel re-inforced method has been attempted for lots of things, like Dome housing, and without careful engineering, and the calculations that you deride, turn out to be dismal failures cracked leaking failures. Domes dont have anywhere near the stresses and strains that boats go through.

    Feel free to proceed with attempt by all means, and ignore all the words of advice. Its your time and money. Please post pictures.
     
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  9. wavepropulsion
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    wavepropulsion Pirate Member

    You never tought in doing it out of clay? Still in use since the 24.000 BC. If the boat fails ever can be used as flower pot, to be sold in the bazaar to barbarian westerners as ''roman art''.
     
    Last edited: Dec 14, 2017
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  10. messabout
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    messabout Senior Member

    R Watson wisely and philosophically said: "It's your time and money" He has perhaps too politely not mentioned that in addition to your time and money, your life is at risk with a boat of questionable integrity.
     
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  11. Milehog
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    Milehog Clever Quip

    He'll be here all week.
    Try the veal.
     
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  12. rwatson
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    rwatson Senior Member

    Its OK messabout, it will never get into the water.
    Like the concrete submarine ... Concrete Submarine Yacht http://imulead.com/tolimared/concretesubmarine/picturegallery/

    Years ago in Hobart, this old guy hired a crane to launch his concrete boat he had been building for 4 years, and as they lowered the boat into the water, it filled up with sea water through all the voids.
    The crane driver had to act quick before the weight got too much, and haul it out before they had a lump of concrete sitting on the bottom next to a commercial wharf.

    Rather than pay for landfill, he donated it to a local council who tidied it up for kids to play on.
     
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  13. dsigned
    Joined: Aug 2017
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    dsigned O.R.C. Hunter


    A couple of things:
    I think your big issue is going to be water seepage if you're at an actual beach, or anywhere that has lots of water.

    That said, if you were to dig out a female mold, I would think using lime or something similar (concrete even) to stabilize the form, and then some sort of plaster (or automotive filler) to finish the mold, then some sort of sealant to give it a good surface finish. Then get a mold release agent, and lay your concrete.

    One more thing: how are you going to get the boat out? Will you just dig it out? How will you raise it? How will you break the female mold? If you go with a more solid female mold, it might be worth making one or more separations in the mold, so that it will come apart without having to break it (e.g. you wouldn't want to take a sledgehammer to the mold, only to crack the hull underneath).
     
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