Building a $20 boat

As previously mentioned my 5 year old wanted to participate in the community anything that floats competition . Rules are that you have to build the boat yourself and spend no more than $20.

I found this plan:
http://applied-sciences.net/library/kayak/
which used coroplast which I was able to get for $17 a sheet.

Here’s the first steps…


I used the lowrider to draw the cut lines on the coroplast and a razor knife attachment to attempt the cuts. Had to help the cuts with a utility knife.


Dalton drew the crease lines onto the boat and used a screen spline tool to make a crease… dad helped a bit on this.


A bit of origami and some tape and we have something boat like.

I’ll post some more pics of the finished project and a vid of the race in August.

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That looks great! His proud smile is the best part.

Have you seen the Oru kayaks? Looks like they start with a bigger sheet but it’s the same basic material you’re using.

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Colorado school of mines (the engineering school I went to) has a “cardboard boat race” on the local spring in April. IDK the exact rules, but paint and duck tape are allowed. There are a bunch of huge barges and giant box ones. But I love it when people try to make a canoe. Thousands of years of design are no joke.

They do “heats” and then a final race. Almost none of them make it a second time. :slight_smile:

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Yeah I saw them on shark tank I was excited till I saw the $1200 price tag. I’m too cheap for that.

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Oh man I think the little ones around here would love that. I am going to drop some hints and see what they think. Super cool!

It’s really a fun mix of boatbuilding “Techniques”. The winner at the last race we entered made a dugout canoe using laminated layers of pink foam sheets then carved it it out. Someone else made a raft out of a tarp with rolled edges coated in epoxy

The boy scouts who enter our community race always try to do it your style with cardboard and duct tape. I’m not sure if any have ever finished the race but their boats are … primitive.

I went with the coroplast for him because he’s 5 and is going to flip it and at least it won’t get soggy. Pretty sure the competition will include me going for a swim at some point.

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I expect there’s enough detail revealed on their site to get you close to being able to “fold your own.” I’d never propose trying to sell one, but for personal use there’s no way they’ve locked down the IP around folding coroplast.

Nice idea ,too complex for an afternoon build with a 5 year old but doable. Their production model uses internal bulkheads to beef up support but I’d still worry about the durability of the coriplast for everyday use. Dalton was breaking through the skin in a few places while using a pencil. A rocky beach would be end of game for this hull. I think Oru must use a different grade skin than HD offers.

I can see the Oru being great if you lived in an apartment or wanted to pack a boat on vacation. We live across the street from the water and have a veritable fleet of kayaks under the porch that we can easily drag to the water so this boat is more of a summertime craft project for us.

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Well the sea trials didn’t go well. The boat was a pretty unforgiving design and he’s not experienced enough to keep it from tipping. I’m going to attempt to modify it later today by opening up the rear to make more of a flat bottom to add stability.

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Enough scraps left over for a small outrigger or two?

Awesome boat!!! I did a cardboard boat race years ago and had a blast. Nice job!!!

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Impressive project! Good idea to make the boat flatter, to improve sideways stability. If it’s supposed to have decent directional controls, for speed and maneuverability, you should have some kind of keel under the flat bottom. But that might be outside the limits of the project?

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Here’s the mark 2. I unfolded the back end and added a floor board to flatten the bottom. It should work if the backend doesn’t go under.

Looks kind of like a paper airplane.


I played with the idea of outriggers but there isn’t much to the boat to attach to. I’d have to do some kind of floating cradle that doesn’t really attach to the hull.

The skeg/fin idea is good if the boat floats.a

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Here is the sea trial for the mark II



I think glueing a couple of pool noodles to the rear sides would stabilize the boat a bit more but overall little man did good.

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So did Dad! Spending time building something is the trophy you already won.

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I’m impressed with how well your son seems to take falling in the water!

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Way to go! Looks like he’s having a blast