concrete kayak/canoe

[giladnaor]

hi,
i am in need of dimensions and profile plans of kayaks to get started.
i would appreciate any other info wich could help me with my design.
thanks
gilad

[mcollins07]

Since concrete is a relatively heavy boat building material, the greater length and displacement is probably better. Of course there are many practical factors limiting your personal requirements on size. How large do you want to go?

[Stumble]

I think a concrete kayak is pretty much doomed from the start. It will be much heavier than other materials, and be more expensive and time consuming to build. For that it won't provide much in the way of benefits. Try taking a look at a skin on frame, or wood one, easier to build, faster, and cheaper.

[Boston]

the effort to row it will be huge. A material like concrete only becomes viable at larger sizes where the ratio of weight to displacement is higher.

I'm just not really seeing it but your welcome to try.
cheers
B

[Jeremy Harris]

Have you looked at the many concrete canoe designs already around? They work well, and have been an excellent way for students to optimise materials that might not at first seem a good choice for such a boat.

The use of pre-stressed/tensioned aramid and carbon fibre members, plus composite reinforcing mesh, has allowed remarkably light and strong concrete canoes to be built - as a search of this forum may show. A quick web search using "concrete canoe" as the search term will give masses of hits on the many high tech designs around, mainly those in the very well supported ASCE competition that's been running for years (see here: http://www.asce.org/Student-Organiza...Canoe-History/).

[Stumble]

Jeremy,

This proves that you can build a canoe out of concrete, not that it is a good idea. The top flight teams are using prepeg carbon fiber, multiple specialty mixes of concrete, 30' autoclaves, and hundreds of civil engineer hours designing the thing. All to achieve a conoe that is much heavier and more expensive, and has less performance than an injection molded one from west marine. This is a perfect example of the adage that just because you can do something doesn't mean you should.

If the OP is thinking of entering the concrete canoe competition that is one thing, otherwise it is a silly material for canoes.

[Jeremy Harris]

Originally Posted by Stumble

Jeremy,

This proves that you can build a canoe out of concrete, not that it is a good idea. The top flight teams are using prepeg carbon fiber, multiple specialty mixes of concrete, 30' autoclaves, and hundreds of civil engineer hours designing the thing. All to achieve a conoe that is much heavier and more expensive, and has less performance than an injection molded one from west marine. This is a perfect example of the adage that just because you can do something doesn't mean you should.

If the OP is thinking of entering the concrete canoe competition that is one thing, otherwise it is a silly material for canoes.

Well, maybe he is entering a concrete canoe competition. He's a non-native English speaker, I'd guess, as he's from Israel, who asked a reasonable question on this forum and got the usual crap from those here who rejoice in putting people down.

FWIW, pre-preg isn't used in composite reinforced concrete, and the very last thing you'd want is an autoclave, as best strength comes from curing the concrete slowly and keeping it wet. The composite tension members will usually be thin pultruded CF rod, and the mesh will be pre-cured composite, often CF.

The OP didn't say why he wanted to do it, but I think we owe it to him to give him the benefit of a balanced view. The ASCE competition has developed first class skills in our future engineers, perhaps the most important being the usefulness of not being blinkered by convention.

I'm not suggesting the concrete is an ideal way to make a light weight, strong canoe, but it does work and if the OP wants to try it as either an experiment, or as part of a student competition, I think we have a duty here to give him balanced advice.

[Boston]

well ya learn something new every day. Who'd have thought they actually do make a concrete canoe, Insane. My apologies

wow

[Boston]

Jeremy, I don't think anyone got after him at all. I've seen it get ugly around here and that wasn't it. I'm curious to see him try though, just as I mentioned in my first.

Anyway welcome to the forum and looking forward to seeing what you come up with

cheers
B

[Lister]

I saw years ago the international competition for building concrete canoe.
the result was astonishing, the thickness of the hull so thin, it was remarkable. some competitor went with classic steel, but I don't know how they did it, but it was beautiful.
Give to the students, they are not shy to try what boat expert says its impossible. And succeed.
By the way it was a contest between engineering school.

[Stumble]

Lister,

That competition is still going on, and it is pretty cool to see what they are doing with concrete. But it is more of a goof project than serious. For instance only 25% of the score is based upon the performance of the canoe.

And I was serious, they are using carbon fiber preped fibers to reinforce concrete. Which requires specialty formulated concrete to kick before the preped goes off. Again a cool application of technology, but completely impractical.

[giladnaor]

hi again,
sorry for not replying earlier as it was nightime here.
i should have said it in my original post. this is for a concrete canoe competition i am entering as a 3rd year structure engineer student. i just recieved a mail saying the dimensions should be: length - 500 cm give or take 3 cm and width 80 cm give or take 3 cm. my problem, as i see it, is how to determin the thickness as it will help me with deciding on how to reinforce the canoe. and of course the height. that is why i asked for references to canoe uilding plans to see how the are built. i wild appreciate any information that would help me in my design.
thanks again, and sorry if my english does not make sense. i think the general idea of what kind of help i need is in the message.
gilad

[Leo Lazauskas]

Originally Posted by giladnaor

hi again,
sorry for not replying earlier as it was nightime here.
i should have said it in my original post. this is for a concrete canoe competition i am entering as a 3rd year structure engineer student. i just recieved a mail saying the dimensions should be: length - 500 cm give or take 3 cm and width 80 cm give or take 3 cm. my problem, as i see it, is how to determin the thickness as it will help me with deciding on how to reinforce the canoe. and of course the height. that is why i asked for references to canoe uilding plans to see how the are built. i wild appreciate any information that would help me in my design.
thanks again, and sorry if my english does not make sense. i think the general idea of what kind of help i need is in the message.
gilad

I used to get a lot of emails asking for help with programs Michlet and Godzilla. They are free and might help you with some aspects of the hydrodynamics. I suspect that more sophisticated tools are being used now.

See:
http://www.cyberiad.net/michlet.htm

Good luck!
Leo.

[mcollins07]

As in most engineering design methods, you will need to make several iterations in your decision process. I'd suggest taking a guess, such as 1 cm thickness, then calculate an estimate of weight, then look at the stresses.

Getting a good strength to weight ratio is always important in boat building materials. Consider fillers for the cement such as poraver. This thread might help: Poraver - is this new?

Similarly on shape. You can start with comparing simple shapes, a half cylinder and a rectangular box, then refine your shape to a canoe shape as you refine your estimates of thickness and material composition.

Since, there will be several iterations of the calculations, you might as well start in a spread sheet, such as MS excel.


~ Michael

[mcollins07]

You need an idea for water line length (Lwl), maximum width of beam(Bm), and the total weight or displacement, then you can use Michlet to refine your canoe shape.

I think you will find, the longer the length for the lower amount of weight, the faster boat you will have. You will probably need to use another free software called Freeship to help create the input for Michlet.

Hopefully, you have a team working on your project, so individuals can take the initiative in the different areas which can be worked on in parallel. The learning of freeship and michlet is a reasonably large task and could be one persons assignment. It is important to gain proficiency in testing the properties of the composit that you design. Someone else to take the lead on making test on the materials. So, the number of people you have and the time frame will be signficant in setting your objectives and goals.