Materials List-
Concrete
Water
Rubber Gloves
Silicone Spray
Boat shaped mold (I used a Tupperware bowl but almost anything can be used)
Bucket to mix concrete in
Step 1:
First create a mold of the shaped boat you want. My mold was a medium sized plastic Tupperware bowl, but you could create one out of wood, Styrofoam or anything else.
Step 2:
Coat the mold with silicone spray so that the concrete will not stick to it.
Step 3:
Put the concrete in the bowl and smooth it out with your hands until it is distributed evenly.
Step 4:
Let the concrete dry for at least 24 hours and then remove it from the mold. Now let it float! (:
Mix the appropriate amount of concrete and water together, make sure to wear rubber gloves!
































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http://www.instructables.com/id/Smash-and-Grab-BowlCast-Concrete-Glass/
http://www.asce.org/concretecanoe/
Rowboats were actually one of the first things built (and sold) by the guy who invented steel reinforced concrete back in 1848 or so http://en.wikipedia.org/wiki/Concrete_ship
Ships were made of concrete, and some boats still are (I don't think anyone is currently making big ships from concrete).
There were also proposals to build various things, including floating docks and perhaps ships from pycrete.
And they did actually get it to float.
Concrete yachts are pretty common. Usually known as "ferro" boats. A famous concrete racing yacht was/is "Helsal II".
You can use wooden molds, and the release agent on that is oil - but on a small boat mold, I suppose that a good sanding of the mold, and a coating of vaseline would be fine.... or layering of urethane paint or food wrap.
And you can look at reinforcement.
Positive or male molds are good to work with as well.
That way you can use a wire probe to get an accurate thickness and you can have a crack at making a boat with sails etc...