help me...concrete canoe

Anna Paul · Feb 15, 2013

Petros said: ↑

Anna,

Sounds like a fun project. Canoes are not really "analyses" in the engineering sense since they are traditional craft their design details have evolved over many centuries, much of traditional boat building is done this way. Unless this is part of your project assignment the best thing to do is to look at popular traditional designs and do a back analyses the strength of the structure, and than choose allowable stresses of your proposed materials.

If you need to do this as part of your presentation than this is how I would model it since I have done so with the 12 or more kayaks and canoes I have designed and built: treat the length of the canoe as a uniformly loaded beam, but inverted. If you will have say 2 crew in the hull, it is two load points with the water pressure supporting the hull as the uniform load (do not forget the weight of the hull which will not be insignificant). Also, look at a worse case scenario with most of the carrying capacity at the center, with the water supporting the hull. the load diagram inverted would look like a beam balanced on a point (like a teeter-toter), with a uniform load along its length (the water pressure supporting the hull).

The structure of the canoe can be treated like a truss or I-beam, the gunwales are the compression members and the bottom is the tension side, the sides are the web of the truss. Use a fairly generous safety factor of about 1.5 or more, also consider maximum load the total displacement volume of the hull with no freeboard (water level right at the gunwale height), this should give adequate strength. they do not really travel fast enough to be concerned with dynamic loads, canoes are not usually designed for whitewater river running. for normal flat water travel you will want 4 or more inches of free board at your design load of course (for kayaks I usually figure much less, but for a canoe I would want a dryer ride).

Also consider the side loads on the hull, since it is open top you will have the water pressure pushing the sides inward. Again take the max pressure as the water pressure with the canoe with the water at the gunwale height, and than a safety factor (might consider going as high as 2.0 for this condition).

It depends on your design rules and allowed materials but I would design several floor stringers of either metal or composite that has good tensile strength, and than design the gunwales for compression with at least one metal stringer in each gunwale. watch out for buckling of the gunwales, you will need thwarts to brace the gunwales about every three feet or so. If possible I would use number three rebar as stringers, welded into a frame (or wired into place), and than use a metal mesh on bottom and sides to form the web/side wall strength. there are many other ways to do this, I think I have seen it done with several layers of metal mesh and only use stringers at the gunwales. And of course make the concrete thickness as small as possible, you just need enough to make it reliable water tight, and to stiffen the structure. Use lots of paint to waterproof the concrete if the rules allow.

About the hull design, the fastest shapes are very narrow beam with a round bottom (low wetted surface), the problem with that is a hull like this is very tippy and unstable. So you will want a fairly flat bottom and enough beam to keep everyone comfortable that will be your crew.

Also, search the internet for what others have done, there are lots of examples to learn from. This contest was old when I was in engineering school 35 years ago. Our team at CSULB (Cal state Long Beach) won the design and presentation award, though the quality of the build was rather poor and way too heavy and it did not perform well.

Do your homework on it and win or lose, you will learn a lot and have lots of fun.

Good luck.
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sir, thank you for your suggestion and I'll work on it.

Actually I got the idea of this project from a competition conducted by American Civil Engineers Society, I've got many design papers posted by the contesting universities too.The materials and methods adopted by them is not available in my place (I'm from Kerala, India) so I have to find a different way of approach, rather than making use of their paper.That is the biggest hurdle im facing now. Im sorry if i've offended you,sir.

Anna Paul · Feb 15, 2013

messabout said: ↑

Annna; I will not add to the excellent design commentary posted above.

A tid bit of advice:
When you do the build, there will be a lot of messy concrete work, much of it with your hands instead of trowels. Beware. The stuff can cause painful lesions on body parts in frequent or continual contact with the concrete mixture. Among those who work in concrete, they are unaffectionately called strawberries. Not a danger if you use nitrile gloves while making those mud pies.

Good luck with your project and keep us informed about your progres.
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sir,what you've said is absolutely right, and ive already hurt my hands.Thank you for your concern, i appreciate it.I'll do use gloves while i work on with concrete

Anna Paul · Feb 15, 2013

The pic shows the canoe(in ANSYS) im working on.This is where ive reached.I ve to find the forces acting on it and boundary conditions to do the rest of analysis.

MikeJohns · Mar 5, 2013

Cheap material in some parts of the world. But you would want inbuilt floatation.

mcollins07 · Mar 5, 2013

This material Poraver is very useful in a concrete canoe.

http://www.boatdesign.net/forums/materials/poraver-new-35743.html

Petros · Mar 5, 2013

I did a google image search and seen the level of sophistication has changed quite a lot since I was in engineering school. some of the hulls look very sleek with a very thin and lightweight looking hull. I am curious about how they are reinforced. One image looks like steel cable stretch over a male mold with carbon mesh filaments before covering with mortar. I wonder what the concrete mix is composed of. most of the winning designs has very smooth hulls, very professional looking hull shapes with a smooth and shiny surface.

I also noticed that in every image where they are handling wet concrete, all had gloves.

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help me...concrete canoe

Anna Paul Junior Member

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