Modern boat made simple, ferrocement flat sides and bottom and top

Discussion in 'Boat Design' started by mustafaumu sarac, Jun 6, 2018.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    I did see a doco featuring a fishing boat around 7 metres or so, I think in Bulgaria/ Black Sea, that looked for all the world to be ferro-cement, so maybe it is a thing in that part of the world.
     
  2. Rurudyne
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    Rurudyne Senior Member

    RW, I think a lot of the appearance problems with ferro come down to a lack of fairness in the underlying armature. Any defects in how well the mesh have is faired must show in the skin and it seems to me you're only gonna need more cement, and thus more weight, to cover up same where it happens. Folks talk about needing good plasterers, and they do, but that's where a relatively small amount of time is spent putting together a ferrocement hull.

    There is a solution that involved a female mold which was plastered and the the mesh pressed into to the concrete, more concrete applied and then more mesh, that apparently produced really nice looking hulls but at that point one has already got a fair mold that could be used with other materials.

    That said, there's been a lot of progress in the high strength cements, particularly on the tension side which is where most crack development is gonna happen.
     
  3. rwatson
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    rwatson Senior Member

    Did I say anything about appearance ?? No, I didn't think I did. That's a whole different issue.

    The "loss of value" may be due to unfairness, but it's mostly because a bad ferro job , OR a bad repair, can be impossible to detect until it's too late, and then it's really serious. It's like buying a used motorcycle, only worse.

    And as for the "female mould" with steel pressed into it - I have never heard of that being seriously attempted due to the extra labour in creating the mold, and then making sure that your had an entire steel armature welded, tied and faired to lower into the mold.

    Finally "high strength concrete" will NEVER come close to not needing the steel armature - it's just physics.
     
  4. Rurudyne
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    Rurudyne Senior Member

    Actually, the method I mentioned doesn't use a fully assembled armature.

    I didn't mean to imply high strength concrete would not use an armature. Only that it's use could address some of the issues with FC.
     
  5. David J Ritchie
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    David J Ritchie Junior Member

    I think reinforced high strength concrete slab poured down low below the waterline would make a good ballast

    Why not have the concrete exposed to the water?

    This would be for designs relying upon static ballast anyway

    however

    Above the waterline, tying into the concrete slab, i would build with a material having a much better strength to weight ratio.

    I don't like any skinny concrete forms being involved, and load bearing with them is right out.
     
  6. trip the light fandango
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    trip the light fandango Senior Member

    Ferro cement solves the main problem that a steel hull has, a need for careful and consistent painting and maintenance, both sides, and thinning from uneven hardening from working/flexing, and wear. . If the wire mesh is poorly pulled in to the main steel rods, not enough twisted ties,or poorly plastered, air bubbles, too thick/wet etc then that boat will be crappy and scrapped within 20 years. If the correct procedure is employed[dry mix worked in evenly from both sides ] then ferro is at least as long lived as fibreglass, ...although with a much worse resale value. Because ferro cement combines an alkaline with an acid it can create a very stable compound a little like coral,.. calcification... if you hit something Ferro can flex without damage and modern strategies can be a permanent fix, hunting cracks in the cement, it can reseal. ferro is more of a" living"hull than the others . I'm a fan, I didn't want to come out but this thread just dragged me in..ha ... it's done now .. They can represent great value for money, it is just the resale that spoils them. new repairs and enquiring as to how they went about it should tell you what you need to know about a ferro, being basically steel apart from a 3to5mm skin of crete protecting each side of the armature, too heavy for anything under say 40ft generally. The hollow tube steel jobs made to be light weight/faster are also dependent on how careful the builder was and you would perhaps take a core sample of one of those suckers, a bit spooky, repairs aren't hard on a ferro, just do it properly. I bet the guy who started this thread stopped reading ages ago, ...because his idea was silly.,..it aint a house slab..
     
    Last edited: Jul 4, 2018
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  7. fredrosse
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    fredrosse USACE Steam

    Mustafa Umut Sarac in the first post indicates $100 for a concrete truck. That may be the price where he is, for typical poured concrete with a large fraction of stone mixed in. A ferrocement hull should be made with a very rich mixture of mortar, with no aggregate stones, and double the amount of portland cement. Mixing up a concrete truck with that stuff would be far more expensive.

    Then there is the thickness he mentions, far far below what is reasonable for a concrete hull. I did my college engineering thesis on ferrocement marine construction, with test panels constructed of 3/4 inch (19 mm) and 1-1/2 inch (38mm) thick test pieces. Test slabs were steam cured, and tested to destruction. The best panels used galvanized expanded metal lath, at about 5% steel cross section in the matrix. Chicken wire and hardware cloth tended to catastrophic failure in the testing machine. A few years later (1973) we made a 30 ft ferrocement sailboat, with large bilge keels to allow beaching, and it is my understanding that this boat is still in use (2018). A crew of 20 young men worked from sun-up to sun-down to plaster the hull, and the steel and wire mesh work took months of preparation for plastering day. The 3/4 thick panels were considered appropriate for a 30 - 40 foot boat, more or less.

    Making reasonable panels, 10mm thick, with the concrete truck (holding several yards of mortar, ready to start hardening) standing by to make the pour, would have the requirement of about 50 skilled workers ready to try to make the panels with success. Mustafa Umut Sarac obviously has little practical experience in this matter, and should make a panel about 10 inches x 50 inches x 3/8 inches (250mm x 1250mm x 10mm) just to get a small perspective about his ideas.
     

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    Last edited: Jul 8, 2018
  8. trip the light fandango
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    trip the light fandango Senior Member

    A cross section of a ferro would be something like 2x4 mm rod ,plus 4x1.5 mesh[gal. bird wire, 12mm hex.] and say 3mm x2 concrete each surface, so 22mm overall, but 19mm is what the old ferro book I have says . A core sample that fell in between the bar spaced 100mm apart as squares would be 6mm mesh and 12 mm concrete worked into the cavities created by the mesh.
    So roughly a ferro cement boat including extra rod for keel, stress points,etc is approximately 65 % steel at least, very much a steel boat with a thin protective skin of concrete . A steel boat is alive with potential rusting if the paint allows through oxygen carried by water or air, a ferro done properly is alive with the alkaline bonding with the acid, which is a more neutral outcome. The concrete skin on a ferro is thicker and more resistant than paint to damage, and a ferro is also painted. In the 70s at least one ferro raced in a Sydney to Hobart, a Rorc, these were made with hollow tube to keep the weight down, I'm not sure how the oxygen in the tube was treated if at all , I'm not sure how it placed, it didn't win, it was up for sale a few years ago with a little recent damage to the stern, $3,500 ?, a nosey at the tubes would have been interesting. You can leave a sound ferro boat for 10 years or longer without issues to the hull itself, a steel boat would need to be painted beautifully inside and out,, everywhere, it might cope. I did say I was a fan.
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    The amount of oxygen enclosed in a tube would be so little, when it was expended oxidising the iron, the rust would be barely perceptible.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    One application of relatively thin (about an inch, in this instance) ferro-cement is laundry tubs, the local variety I am familiar with last forever, and I have yet to see any signs of swelling of the re-inforcement causing cracking or spalling. But, of course no salt water contact. Don't know how these were moulded, smooth inside and out, but it has to have some lessons for boat building.
     
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  11. JamesG123
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    JamesG123 Senior Member

    This was going to be my suggestion from his post. It comes in 4' x 8' sheets here in the States. Making the most of a bad idea. lol.
     
  12. trip the light fandango
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    trip the light fandango Senior Member

    It sounds like an atmosphere that would attract water , with hydrogen being able to morph into 50 different compounds, and a marine environment, but if it is perfectly sealed...? The fact that those boats are still sound proves your point.
     
  13. trip the light fandango
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    trip the light fandango Senior Member

    I don't think those tubs have mesh in them, presumably because they don't need to flex like a hull does, they must have been a fine quality aggregate. The only thing good concrete needs to survive is some moisture content.
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    Some do have mesh, I saw someone take to an old discarded double-tub with a sledge hammer. and it revealed a fairly heavy mesh, and he gave up trying to break it up.
     

  15. trip the light fandango
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    trip the light fandango Senior Member

    ...Some do have mesh,.. that helps explain their longevity then, and it is a good example of just how tough ferro is, or can be.
     
    Last edited: Jul 6, 2018
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