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Thread: Designing a new CONCRETE BOAT

  1. #1
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    Lightbulb Designing a new CONCRETE BOAT

    Hello folks! im new to this forum and im about to be part of the canoe racing teamhowever this year we have to build our own canoe but made of concrete!i posted a picture of how i want my canoe to be ( the picture is a wood canoe and i want it to be out of concrete )now here is the deal the dimensions i gave it are 3.20 meters long and width is 82 Cm at the middle of the canoe will it sustain it self in water? which improves can i give to it so i can go faster lighter and comfortable ?can i paddle with my back you know like PROS or do i have to make a regular paddle FACT = ONLY 2 PEOPLE CAN PADDLE thanks i hope you reply!
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    Default Re: Designing a new CONCRETE BOAT

    Okay, I'll bite. First, this is the Woodenboat Forum. Why not ask the question in the "Concreteboat Forum?

    That said, the answer to your question is fairly straightforward.

    1. Draw the lines of your contemplated ferrocement canoe.

    2. Using the lines, calculate the weight of your contemplated ferrocement canoe. This should be fairly easy, since most all of the weight will be the hull. The way to do the math on that will be found in any elementary book on boat design. This is the "displacement" or weight of the boat. This weight will displace an equal weight of water. (See: Archimedes' Principle.)

    3, Using a compensating polar planimeter (available on eBAy) or one of the less accurate manual methods, calculate the buoyancy of your canoe. The buoyancy is the weight of water that the space of the interior of the canoe would contain if it were filled with water.

    4. If the displacement, or weight of your ferrocement canoe, is greater than its buoyancy, it will sink like a stone. To the degree its displacement is less than its buoyancy, it will float. If it's greater, again using your polar planimeter, or a manual method, calculate the point in the section lines where the displacement and buoyancy are equal. This will give you the waterline and from that the amount of freeboard will be apparent. Obviously, the more freeboard, the better, because, unlike a wooden canoe, a ferrocement canoe will decidedly not float if swamped without floatation foam or airbags, the size of which, and therefore their buoyancy, will have to exceed the
    displacement of the canoe.

    Or.... you can just take my word for it. The prospects of success are close to nil. It would appear unlikely that a structurally sufficient hull could be built thin enough to provide the buoyancy necessary for such a thing to float. Small ferrocement boats have been built. Indeed the first ferrocement boat was a double-ended rowboat built in 1848, not as a practical exercise, but as an exhibit for a trade show. (Pictured below.) From the looks of it, the designer relied on substantial draft to ensure sufficient buoyancy. Ferrocement is indeed a relatively lightweight material for vessel hulls, but this is only true as the size of the vessel increases. At "canoe size," the trade-off reaches a point of diminishing returns. The ferrocement, even with various polymer additives to retard moisture penetration which will rust the ferrous armature and cause the cement to break apart ("spalling") if the metal isn't buried deeply enough in the concrete, would likely require a thickness in cross-section which generally will exceed the buoyancy of small hull.

    Last edited by Bob Cleek; 09-01-2017 at 01:10 PM.

  3. #3
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    Default Re: Designing a new CONCRETE BOAT

    These kind of canoes have been built for a long time. Do a little research on Civil Engineering classes.
    They produce largely worthless boats, suitable only for a one time "race".
    Many break, some sink, none of them qualify as race worthy.

    I sincerely hope you are not spending your own money.

    I'd suggest you build a wood canoe and enjoy it for a while.

    It would be cheaper to make it out of cardboard - there are many "races" for those. Mostly they last about as long as the concrete ones.

    Your basic problem is keeping the thing from sinking. Paddling with your back has nothing to do with it.

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    Default Re: Designing a new CONCRETE BOAT

    A neighbor built a ferro-cement 40-foot sailboat hull in 1977. The job of fitting it out suddenly stopped. And then in 1985 the builder fled the country to avoid prosecution for ivory smuggling, and abandoned the property with the hull on it. Subsequent owners left the cement hull there to slowly deteriorate. Just for fun I looked on Google Earth and discovered satellite imagery showing that the hull is still there after 40 years.

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    Default Re: Designing a new CONCRETE BOAT

    My dad tells a great story of a man that took an age building a ferro cement boat and took it to the dock to get it craned in to the water. I won't mention the port but the dockers where I little militant and talked about permits etc and refused to touch it despite prior arrangements being made.
    They were given some personal incentives and within minutes the boat was high in the air only to make a much more rapid decent onto the quayside. Obviously he was not insured for such a disaster and billed for removing the detritus.

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    My experience with canoes is that sooner or later you will swamp it. Admittedly, I do not claim to be an expert canoer (if that is a word). It seems a concrete one could never be swamped without a rather difficult recovery.

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    Just saw Bob's response, I like the cardboard idea. My older brother had to build one for a freshman architecture class back in the late 70s. It had one successful voyage.

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    Default Re: Designing a new CONCRETE BOAT

    Cardboard, sealed with glass and epoxy, would likely survive a second experience with water.
    "... the door was ajar, and the game was afoot." Lawrence Block

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    Default Re: Designing a new CONCRETE BOAT

    This was an engineering challenge at Lafayette College for the engineering students for years. Don't know if they still do it. But from the link above, yes, a usable boat can be built. And as can be seen, it doesn't have to be all that heavy. If it wasn't for a race, I'd just take a canoe I liked (but not too much) and use it as a mold. Of course, care has to be taken that the two will come apart once the concrete has set.

    30th Annual NCCC Races by American Society of Civil Engineers, on Flickr
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    Default Re: Designing a new CONCRETE BOAT

    Just a historical note. Most folks associate ferrocement boats with the 1970s, but their history goes back much further. Ferrocement barges played a crucial role in WWII in the Normandy invasion. I was able to see some when I was in Europe in the 1960s. Pretty long lifespan for "temporary" boats.
    Everything changes . Everything is connected . Pay attention

  12. #12
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    Default Re: Designing a new CONCRETE BOAT

    Given that the global need for concrete in building far exceeds usable sand for the aggregate, there have been some fantastic advances in lighter structures using different, often foam, materials in the aggregate. Are you looking at that as well as how to lighten the armature.

    On the armature, you might (building on a male mold) have one or two layers of fairly shear open weave fiberglass on the inner and outer surfaces and no heavier central armature. That coupled with granulated foam in the aggregate could make for a light structure.

    Your design proposal, while a pleasing shape for a canoe-looking canoe is not a very fast shape. The organized races are going the same way to once popular "Sikaflex Challenge" went design wise - more extremes of long length and narrow width.

    G'luck

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    Default Re: Designing a new CONCRETE BOAT

    The advice contained in this thread is - at best - worth all of what you paid for it - no sane man, other than a historical re-enactor, is going to use a mechanical planimeter - that sort of stuff is much faster and simpler with free software such as "Freeship"....

    http://www.asce.org/templates/events...x?pageid=15779 - gives a list of racing concrete canoes - most of which are between 5.5 and 6.5 metres in length and between 70 and 150 kilos in weight.

    A standard bad mistake is to copy the shape of conventional racing craft (weighing under 20 kilos) in concrete so that it weighs 150 kilos.... a better starting point would be something like a "prospector" which is optimised for two paddlers and a heavy load of gear.

    N.B. it is possible to make concrete which floats - the key is in the choice of aggregate - vermiculite is a good starting point.


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    Last edited by P.I. Stazzer-Newt; 09-02-2017 at 09:35 AM.
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  14. #14
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    Default Re: Designing a new CONCRETE BOAT

    On the ferrocement boat craze - a viable technology way way oversold. Hull material is not even a quarter the total cost of a boat so save as much as you want there, you only save a few percent on the whole boat. Just as with all too many wooden boats and back yard metal boats, many were rather poorly made. But when made correctly, they are fair, strong, durable, and suitable to the purpose. It's just that in today's world, designers like Colvin and Buehler have plans readily home built in metal or wood at a gross cost that's quite appealing.

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    Default Re: Designing a new CONCRETE BOAT

    hey do you mind helping me on my project.. i mean by the answer u gave u must know a lot and it would be really helpfull please

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    Default Re: Designing a new CONCRETE BOAT

    Quote Originally Posted by germanhiguerav View Post
    hey do you mind helping me on my project.. i mean by the answer u gave u must know a lot and it would be really helpfull please
    Could you explain what the boat is for? That might help us help you.

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    Default Re: Designing a new CONCRETE BOAT

    it is for racing.. two people only and well.. thats it
    the dimensions i chose are 3.20m long and 82 cm at the middle is that ok? or will it sink?

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    Default Re: Designing a new CONCRETE BOAT

    Two layers of 20 guage x 10mm high tensile mesh with 3.5mm high tensile reinforcing rod around the gunwales will, if you are careful with the plastering give you a skin thickness of around 8mm. Thats not impossibly heavy. I've a friend with a ferro Bingham "Flicka" with a hull thats only 12mm thick, she's underweight compared with some of the fiberglass ones and she's done several quite notable ocean passages.

    On calculating displacement, you can use graph paper rather than a planimeter, a hint though, doing it in metric is much much easier.

    John Welsford
    An expert is but a beginner with experience.

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    Default Re: Designing a new CONCRETE BOAT

    There's an absolute treasure trove of detailed information in the link Stazzer-Newt gave you up above. Not just pictures of successful boats, but the technical papers submitted by the teams. It's a lot of heavy reading, but if you want your project to be successful, chow down and digest it! Here's the link.

    I found the variations in weight alone quite surprising. From under 200 pounds to about a ton. Good luck!
    -Dave

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    Default Re: Designing a new CONCRETE BOAT

    but isnt 19ft a LOT for 2 people only ? i mean that just increases weight distribution
    wouldnt be better just a 11ft ?

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    Default Re: Designing a new CONCRETE BOAT

    maybe the thickness of the hull could be about 12mm shouldnt sink right..

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    Default Re: Designing a new CONCRETE BOAT

    You're the student. Run your numbers.

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    Jay Bedford had a method called wireplank for lightweight concrete hulls. Might be worth looking up. The original Helsal racing yacht that won the sydney hobart was post stressed and used fine stainless strands to reinforce the outer layers without the rust issues. Ians Fibreglass idea seems good. Prehaps carbon fibre strands could be used?

    Some really good FEA on the hull would identify the parts loaded in compression vs tension and enable much better optimisation of the heavy materials.

    Calson hulls is a simple bit of software that enables quick hull design. Then import it into freeship for tweeking and into mitchlet for improved resistance calculations. It's also easy enough to export from freeship into something like Rhino or ACAD and onwards for FEA calcs.

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    Also remember with ferro the curing process is critical to optimum strength. Traditionally it took a few weeks of continuous careful soaking (or steaming) to acheive a full strength mortar. Might be worth scouring the libraries for old ferro cement boat building books from the likes ofJay Bedford, Bruce Bingham and Hartley.

    I would have thought 3mm would be a better target hull thickness.

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    Default Re: Designing a new CONCRETE BOAT

    Quote Originally Posted by germanhiguerav View Post
    it is for racing.. two people only and well.. thats it
    the dimensions i chose are 3.20m long and 82 cm at the middle is that ok? or will it sink?
    Canoe races come in many different formats - flat water, rapid, sea -- over distances from a couple of hundred metres to over two hundred kilometres - sometimes involving tight turns and twists.

    Course type and distance?

    Do the rules define "Canoe".

    Do the rules define "Concrete"

    How much paddling experience do the two people have? - Any race experience over this tyoe of course?

    Single bladed paddle or double blade?

    What do you know avout optimal paddle length?
    3.2metres is a very short boat for two people - in general longer is faster and lighter is faster - as boats get longer they get heavier, so there is a careful compromise to be made - given no rule restrictions , and full strength eperienced adult paddlers - I 'd expect the winner to be somewhere between 4.8 and 6.2 metres and with a waterline beam under 60 cm.

    Be under no illusion that this is a quick easy thing to win.
    Last edited by P.I. Stazzer-Newt; 09-03-2017 at 04:02 AM.
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    And don't forget about stability. For a pair of novice paddlers, trying to keep a narrow canoe upright while paddling hard is tricky.

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    "3.20 meters long and width is 82 Cm at the middle of the canoe will it sustain it self in water?"

    This gives something like 150-250 kg bouyancy depending on how deep she sits and the exact hull shape. A rough estimate would be something like LOA x Beam x draft x block coeficient. So to pluck some rough numbers from thin air gives 3.2 x 0.82 x 0.15 x 0.45=0.177m^3 or 177kg bouyancy in Fresh water. This won't be enough, so she will need either a fuller hull shape or to sit deeper to carry two crew and a heavy concrete hull. Otherwise the hull could be longer and/or wider. A longer hull is likely to be much faster even if it is a lot heavier.

    Directional control is another thing to factor in.

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    Default Re: Designing a new CONCRETE BOAT

    " . . . a heavy concrete hull." [#27] Maybe not. These are engineering students who can surely research the modern approaches to foam and such in the aggregate. Just because it's concrete does not mean it's a rock.

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    ^^ true, it would be interesting to see what can be done. Ferro cement is an interesting material. And as a one race boat the hull only has to last for the length of the race, so it could be eggshell thin if the design and loads are carefully worked out.

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    Default Re: Designing a new CONCRETE BOAT

    In the Netherlands it was a yearly tradition for Technical Colleges to organize a race for concrete canoes. You could try them. On this forum it is rather impopular,and it is out of fashion. I knew an editor of a British boating magazine who built a concrete version of Slocums Spray and wrote a book about it in the seventies. He is still occasionely apologizing for it.
    Good luck, Frank

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    https://files.asce.org/xythosmobile/...ntriesCount=20

    Looks like everything you need to know about concrete canoes is here. 4500 hours in the winning teams current project!

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    Default Re: Designing a new CONCRETE BOAT

    This is starting to sound more like a science fair project than an exercise in practical boatbuilding. I'll amend my original statements to say, yes, with specialized aggregates the weight can be brought down. The exercise at that point isn't about the cement, but rather about scientific naval architecture, assuming wants to be competitive in such a race. Given your interest in winning, hull shape is going to likely be the critical variable, assuming you can create a cement matrix that is light enough to keep the whole thing afloat.

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    Default Re: Designing a new CONCRETE BOAT

    It would be nice to hear from the OP.
    The responses have been anywhere from discouraging to a college design project to Naval architecture work.

    Germanhiguearav - could you tell us more? Is this a student project at some level? Did you just want to build something? Is this an organized competition? Are you an Engineering student?

    If we knew the answers could be more useful.

  34. #34
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    http://www.asce.org/concrete-canoe-results/

    This link might work better than the other one. Seems lile it was locked for direct entry.

    Seems like the top boats are 19 foot long, 2 to 2.5 foot wide and weight something lile 125-200lbs the hulls are 6-8mm thick and the cement has a SG of around 0.7, so about the same as a moderately heavy hardwood. Using lightweight agregates. It floats!

    Carbon fibre and glass reinforcing is used, PVA strands also reinforce the cement. Post stressing is used on some boats.

    Interesting and impressive work from the next generation of engineers.

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  35. #35

    Default Re: Designing a new CONCRETE BOAT

    the original FLIKA was designed from the get-go to be built in ferro, the design was never adapted from any other medium.

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