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Hand powered boat propellor? Answered

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I am trying to build a boat for a physics project, and i wanted to try building one that used a propellor instead of the usual paddlewheel or oars that other students have used.  I bought a 2-blade trolling propellor from Walmart, and i plan on attaching it to a crankshaft via a 4:1 belt drive ratio (so with every rotation of the crankshaft, the propellor spins 4 times). Two people will be turning the crankshaft , and the boat itself is stocky with a flat bottom and pointed end.
Is this even possible, and will it actually get the boat to move at a reasonable speed? ("Reasonable" meaning rowboat-ish speed) 

I included a quick sketch of what im talking about, and a picture of the blueprints to the civil war submarine that I got the idea from, just for proof of concept. 

4 Replies

steveastroukBest Answer (author)2013-05-06

Do some math.
a.) Find out what the output of the original trolling motor was, and its top speed.
b.) Find out what the rated output of two students' arms is - less than the legs.
This will allow you to get some idea - assuming that your crank/gear is enough to get the prop to the same speed in water.
Build it, test it, repeat experiment using whips on students..........

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iceng (author)2013-05-06

A propeller for low speed RPM is a vastly different configuration ie-shape
then your Walmart 2-blade.


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Kiteman (author)2013-05-06

It will "work", but how well will depend on the propeller - the size and pitch of the blades needs to match the intended speed of rotation and size of the boat.

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rickharris (author)Kiteman2013-05-06

Human output around 1/2 hp for a while depending on your fitness. perhaps a little less for arms

Prop I guess will need to have big blades and a slow rotation for best use of power. I could be wrong and gearing may be a better answer with a more standard prop.

As Stevs says do the maths

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