new way to build concret hulls?

Discussion in 'Boat Design' started by Baltic Bandit, Jan 22, 2014.

  1. PAR
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    PAR Yacht Designer/Builder

    My apologies Skyak. My intent was to suggest that if you're going to climb out on a design limb, there should be a justification and reasonable cost/benefit relationship backing it up. Classic yachts can be easily designed with monolithic modern materials and structures, without difficult to justify contrivances, such as multiple hull materials of greatly differing physical properties. I'm sure it could be made to work, but to what end. The hull will be heavier, which isn't good and compensating elsewhere, is just a design crutch for a poor likely non-SOR decision.

    Simply put, if you want a new 8 meter boat (for example) lots of new interpretations exist, that make far better choices then a concrete/wood composite. Back in '86 I was on the build of an aluminum 8 meter, though had a conventional (at the time) rig. This was an exceptional example of using modern materials, methods and techniques, to reproduce a classic that preformed better than it's predecessors. Folks interested in a classic, will want to justify the costs and its performance, with dramatic changes to it's structure and build type. I don't think a concrete/wood build is an easy sell.
     
  2. Skyak
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    Skyak Senior Member

    My assertion is that there is a market for sailboats that fully replicate classic designs (weight, waterline, righting, moments of inertia...) and that high strength concrete from the waterline down will be a superior way to make them. If you see greater market value in modern plastic boats designed to the old rules well that's your business and it's of no interest for me to try and talk you out of your values.

    Parting shot -Consider it through a customer's eyes -you offer another plastic boat that has 'fine' or 'better performance than a classic' but it is not as fast as more serious and expensive plastic racers. Of course the rating system goes a long way to leveling the results but gives a slight advantage to boats designed to the rule. My boat has performance that is 'legendary' it's just as competitive on corrected time, and it sails sweeter than any of the above.
     
  3. upchurchmr
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    upchurchmr Senior Member

    Your boat is nothing but a fantasy with no practical solutions to real life issues.
    Pick out a classic and lets see a layout and some numbers.

    So far there is nothing even as good as "Popular Science" bluesky claims.

    At least the OP's illustration could provide shelter if you had a fork lift, water, and the starting package in the middle of a disaster. It might not last long.

    OBTW, most concrete canoes had to be picked up by 6+ guys to not be broken in half before it hit the water and another large percentage sank before finishing the race. Not a good recommendation for building something useful.

    Please go ahead and build "your boat". I'm sure you will do well financially.
     
  4. Ilan Voyager
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    Ilan Voyager Senior Member

    Sorry Skiak but your assertions are wrong;
    First; you have transverse et longitudinal stability. And you have also arm of leverage, righting moment and position of the weights. A smaller weight with a long arm is more efficient than a heavy weight...
    So if you want a maximal righting moment in transversal stability (putting beside the problems of hull shape and immersion of volumes) you have interest to concentrate the "ballast" in a dense metal (lead, iron or whatsoever) with the maximal arm possible. That was done by any NA while designing the boat.
    But also the longitudinal position of the "ballast" is of prime importance of a sailboat, or you'll have problems of polar inertia, in plain language that the ballast (and other weights) must be as possible close to center of gravity. Thus the parasitics movements induced by the weights which are far from the CG are reduced as mush as possible; when you examine closely the plans by N. Herreshof or O. Stevens you see immediately that they took the greatest care of the longitudinal stability by centering the weights and by the repartition of the volumes to amortize the pitching. (the good old Bonjean curves). A boat made following your building system will savagely pitch in any sea. It will be impossible to reproduce a Dorade with the same displacement, inertia, righting moments, and seaworthiness with a mix of concrete and wood. It will be very easy to get a better Dorade in cold molded wood, strip plank, polyester, aluminum without any engineering risk: the boat will be sound, and will behave as intended by old Olin the NA. Note that his later classic boats were very different of Dorade which shows now it's very great old age of conception. You're going closer to naval archeology than boat designing.

    May your modesty suffer about the humble assertion of highly effective method of boatbuilding, the joint between the wooden part and the concrete part will be a source of major nuisance as have already experimented all people using dissimilar materials for the hulls and decks of sailboats. You'll make your own experiment...

    Ferro Cement is simple a kind of reinforced concrete with smaller aggregates and a lots more steel (until 40 percent of the total mass) so a good concrete for boats (and for skyscrapers also) it is simply a concrete highly reinforced. The density is not more 2.7 tons/m3 but a solid 3.6 metric tons/m3 and even more. Almost half the density of steel but far less the half of strength, more than twice the density of GRP being far less strong, and I won't talk about wood.
    The bridges in seismic zones have so much steel that you have to use small sized gravel in the concrete mix so the concrete can pour between the steels. And it's heavily vibrated to insure a total absence of bubbles.

    The other difficulty in a yacht with rather thin skins is to get a tridimensional web of reinforcements. It's the Achilles heel in concrete on yachts; difficult to get such a web.

    The tensile strength of cement with aggregate is so low that the lone practical way to get things better is to add a "fiber". Polyester is not strong enough and adhesion with cement is rather low so it's only used as microfiber for fighting micro-cracks or in very lightly loaded structures. Glass fiber is a bit better with a special surface treatment but the most practical is steel as being proved since 100 years. Steel can be protected with epoxy or other and the rust problem can be solved.

    Concrete hulls have been made with a lot of different techniques, additives, fibers, steels, special cements, pure silica sands and tutti quanti. None has been successful enough to appear as a mainstream building method. Besides I have some doubts that someone will buy a concrete-wood mix boat.
     
  5. Petros
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    Petros Senior Member

    you are out of date of what modern concrete canoes look like and how they perform.



    [​IMG]

    [​IMG]

    look how light weight!

    [​IMG]

    [​IMG]
     
  6. PAR
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    PAR Yacht Designer/Builder

    Look how light weight? Really? Given the exact dimensions, what would these so called like weight concrete canoes weigh in other common materials? Would it be lighter than any of the "usual suspects" employed in canoe construction, particularly if the emphasis of these builds, where concentrated on light weight as well?
     
  7. Ilan Voyager
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    Ilan Voyager Senior Member

    There is plenty of documentation in Internet. The material is called concrete because it contains portland cement. But it's very far from an ordinary concrete or ferro cement; it's pre-stressed with a mesh of fiberglash and/or graphite, the list of the additives is longer than the catalog of Dow Chemical, there is more microspheres than in a putty for fairing an epoxy hull. It's simply an engineering concourse, not a practical study for making boats.

    Very hard to find good ciphers but the 2 places weight around 50 pounds et the bigger ones around 180 pounds. It's about the weight of a traditional birch bark canoe for about 100 times the cost of material and three times the work.

    I do remark that the traditional birch canoe can take a lot of cargo and can cope with rocks and fast rivers, these concrete canoes with minimal freeboard are just for a competition on a very calm lake with a mirror like surface.

    It's very fun to see this deployment of technology for obtaining a product inferior to a canoe made with birch bark, spruce root, cedar and pine resin with a good knife as main tool...that's the proof that whatever the refinements, when a material is unadapted for a job you can not get good results. "Romantic" dreams about a material are useless. I would not make a 5 stores building with birch bark...

    For information 2 pics taken from http://ace-mrl.engin.umich.edu/NewFiles/projects/recc.html. They show a lot of information to an trained eye. For example the plllar of the bridge has failed just at the place of maximal concentration stresses because of the variation of mechanical inertia and the change of path of the flow of the stresses.

    Note the quantity of steel in the pillar and the mode of failure of a concrete under dynamic loads . This flexural stresses are very similar to those of a portion of hull.
    Note also that the mix of aggregates and cement literally pulverizes because of the lack of cohesion, and that the concrete does not adhere to the steel...Concrete is not good for a hull. CQFD.
     

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  8. Petros
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    Petros Senior Member

    I would agree with you Ilan on conventional concrete, but I find the super mixtures of concrete used on the canoes technically interesting. I am doing here a mental exercise in perhaps finding a more durable hull material made of some kind of concrete mixure.
     
  9. PAR
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    PAR Yacht Designer/Builder

    Again, even using a technically interesting concrete formulation, what would the weight be, compared to the other usual build methods and materials?
     
  10. upchurchmr
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    upchurchmr Senior Member

    Petros,

    I am very impressed that two people can carry a modern concrete canoe, but what does that say about something with significant loading like sailing loads?
    Do you know what that boat weighs?
    Would it be comparable to a wood or SOF canoe - 30 - 40#?
    Agreed, I am out of date for current construction.
    But I await your answer to PAR.

    A general comment without data does not convince me.
     
  11. PAR
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    PAR Yacht Designer/Builder

    Judging by the photo, both are hefting, not carrying that canoe, which is telling.
     
  12. Ilan Voyager
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    Ilan Voyager Senior Member

    The problem remains the same whatever the aggregate as Portland cement is a weak glue; so you get a juxtaposition of aggregates (from gravel to microspheres) maintained together in contact by cement. In compression it's not a problem as you have only to impeach the aggregates of sliding; furthermore the compression locks the aggregates together; it's even better that the aggregates are not round. In traction it's another matter the concrete fractures at the weakest lines ie the cement joints between the aggregates.

    Even doped by acrylate resins (vinyl resins are too soft), even adding microfibers (polyester, carbon, dynema, steel etc...), you won't reproduce the cross link effect of long molecule chains created by the curing of resins like polyester or others. Or in wood the lignine gluing the long cellulose tubes.

    Or you put so much epoxy that the cement and aggregates becomes mainly a bulk agent...That was made in the 70's with very poor results. Better go directly to epoxy and long fibers.

    If you want results in traction (and thus flexural stresses) you need long chains of molecules of a resin embedding long fibers so the stresses are taken mainly by the fiber. Resin putties are weaker than GRP made with mat, which is weaker than GRP made with cloth, and UDs are even better. In fact you need only the quantity of resin for maintaining the fibers aligned together, thus pre-impregnation, vacuum, infusion methods to get the highest ration possible of fibers.

    The concept of concrete is exactly the opposite and is totally flawed for getting a strong material in traction. Concrete has been invented by the Romans as an artificial stone that can be poured and highly resistant in compression (the Pantheon at Rome is a nice piece of engineering)...Adding steel helps but the reinforced concrete is used because it can be poured in a mold and thus obtain complex long and big pieces used mainly in compression. The intellectual concept of concrete has no use on boats, except barges.
     
  13. nimblemotors
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    nimblemotors Senior Member

    You'll find it on here if you look, as I looked into it, my rough estimations were a lightweight concrete is about the same weight as plywood, but costs a LOT less which when making a very large boat, the cost difference is significant. It doesn't rot, and most importantly, lightweight concrete
    can be formed into shapes using female molds.
     
  14. Ilan Voyager
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    Ilan Voyager Senior Member

    The "mainstream" for concrete canoes is a 9mm thick hull of a concrete made with cement and acrylic resin charged with plastic copolymer microspheres so you can get a density of 600-750 kg/m3 (about the same density as a hard wood) plus fiberglass mesh and microfibers. Stainless steel cables are used to compress the structure and take the traction stresses. The weight (about 50 pounds for a 2 places canoe with a very low freeboard) is about the same as a identical boat made in a 9mm hardwood like ash. But the resistance is far lower. I have not found any physical data about traction, flexural nor modulus: that means that the true cipher are too bad to be published, as any excellent result like a concrete as strong as steel would be published in all the civil engineering mags. Finally I'm sure that you can get similar results with a cross linked PVC foam 100 kg/m3 and polyester tape.
    I remark that none of these canoes has opened a new way for making boats or other objects and have remained just as exercises of style without practical applications...
     

  15. Ilan Voyager
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    Ilan Voyager Senior Member

    The density of plywood is 550-650 kg/m3. I made 40 feet fishing boats 24 knots max speed with 18 mm at the bottom, 12 mm topsides and decks made with a 600 kg/m3 plywood. The oldest has now more than 20 years of fishing 300 to 320 days/year in seas until state 7 without any structural problems. Not a crack, not a rotten piece of wood, not even a loose screw.

    How do you make a hull with similar thicknesses and same weight with a light concrete? Can you get the same strength without using steel?
    Acryl resins and copolymer microspheres are pretty expensive. Fiberglass mesh treated with special silannes for use in concrete is not cheap.
    Also you'll have to use as much epoxy resin to seal the concrete outside and inside as for a wooden boat.

    I would like to see the final weight for a similar strength as a plywood hull. And the true cost of fabrication won't be so low. Concrete is cheap with ordinary sand and gravel a plain tap water, not so much with pure silica sand and volcanic stone gravel. But made with microspheres, doped with acryl and microfibers it's another story....And you have to degaze under vacuum each batch of mix so you are sure that not a bubble air is trapped before pouring or projecting. And it's very labor intensive as all the structure has to be done in steel mesh (or other) and added/or included to/in the hull. Look at some pics of ferro cement building and you'll understand the pain. You do not glue or screw concrete. It has to be of one piece, including all the structure with the hull skin..

    PS Concrete does "rot" in sea water in presence of steel. There is plenty of documentation about the maintenance and miseries of concrete submerged in sea water.
     
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