Cardboard Boat

[JollyJeff]

This year our town started to participate in the "Cardboard Boat Regatta" on the 4th of July. This is where every boat has to be built out of cardboard and run a short race. There are awards for speed, team participation, and the best boat built with cardboard. It was great fun to see everything from giant "rubber" ducky to Sea Hawk football stadium. It was amazing that so few sank.
We won our first round by paddling a six person catamaran but our arms wore out during the semi finals. Which I was glad because I would not been able to make it though the finals.
We have already started planning our next years boat and are looking at switching to a two person arrangement in a shorten catamaran. The question is does anyone have suggestions on propulsion system? We were looking at either a propeller or the mirage drive (which is basically two flippers that go back and forth) driven by bicycle crank set up. (We had thought about a hydrofoil but couldn't figure out how to get the cardboard to handle the stress.)
Our goal is to win the time trials so we need to be able to sprint around a "U" shaped course. I look forward to hearing your thoughts.
.

[Guest625101138]

A stabilised monohull is faster than a catamaran unless you have a length constraint.

A properly sized propeller is roughly twice the efficiency of the Hobie flappers.

Obviously it must only require a cardboard hull because it would be a challenge to make a useful cardboard shaft.

You might get some ideas if you work through this thread:
Pedal Powered Boats

A two person feet-to-feet paddlewheel is not particularly complex and quite efficient if sized properly.

Rick W

[rwatson]

Two frightened non-swimmers in a sinking cardboard boat with paddles would do the trick!

[JollyJeff]

No there is no limitation in the length so we are good there.

What would dictate the proper size for the propeller? Or what would be your suggestion for a size?

The drive train and steering don't have to be made of cardboard but everything structurally does.

thanks for the suggestion on the pedal powered boat. Looks like lots of good information there. I can see how the monohual is faster.

I have to admit that I have not seen a two person feet to feet paddlewheel. I will have to look into it. thanks

[JollyJeff]

That is how we won the first race. The sheer fear of sinking.

[Guest625101138]

Originally Posted by JollyJeff

......

I have to admit that I have not seen a two person feet to feet paddlewheel. I will have to look into it. thanks

Watch this:
http://www.youtube.com/watch?v=-QjRM-cQpHw
The Hydrodynamasaurus is the sort of thing I mean.

Rick W

[JollyJeff]

Wonderful. this really gives me some ideas. It would be wonderful if I could figure out how to create a hydrofoil from cardboard that would hold up for the required three races. Well at least I have a year to beta test some ideas. Thanks again

[Guest625101138]

Originally Posted by JollyJeff

...... It would be wonderful if I could figure out how to create a hydrofoil from cardboard that would hold up for the required three races. Well at least I have a year to beta test some ideas. Thanks again

If you have a solid box beam above the water surface you could use four vertical struts from the beam to the foil and a fifth from the centre of the hull to the foil.

The foil would need to be have about 5" chord.

If you are permitted to use heaps of cellotape it would be possible to make quite a solid foil building up cellotape on a cardboard former. The tape would have a few transverse layers top and bottom. Then some wrapped diagonally back and forth and then some more transverse layers and so on. You would make it about 1/2" thick with a flat bottom and convex top. The foil width would be 8 to 10 feet.

This might have sufficient rigidity.

The value of the foil gets down to how long the race is. You could make a displacement boat around 24ft long that two people could hold around 14kph. You need a reasonably good foil to better this for anymore than a few minutes.

Rick W