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Old 07-05-2021, 09:53 AM   #115 (permalink)
RedDevil
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Found it!
http://202.38.64.11/~cxyu/AJP_pushmepullyouboat.pdf

Quote:
... We have demonstrated
such a boat at recent pvblic displays in our junior level
physics laboratory. A typical nonphysicist is suitably impressed by the novelty of the boat, whereas the initial response of people with· some physics background is often
one of disbelief. Being familiar with the laws of energy and
momentum conservation, they feel that somehow these laws
are being violated. Indeed, a detailed analysis of the device
is an instructive application of these laws, suitable as an
undergraduate physics exercise. (The topic also aroused
considerable interest when given to a graduate physics
problems class.) We present such an analysis here. ...
Note that in the PMPYB the air propeller is used to power the water propeller to push the boat against the wind.

The distance the air moves through the propeller is greater than the propeller covers in the water, therefore the wind will force the propeller to turn with the wind despite the water propeller resisting it, as the latter covers less distance while the force on both propellers must be about equal.

It could be inverted by using a wind propeller with almost flat blades and a water propeller with an aggressive angle of attack, so the latter covers more distance for each rotation.
In that case the force on the water propeller produces more torque than the force on the wind propeller, making that turn against the wind.
The boat then would run with the wind faster than the wind (at least theoretically).
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Last edited by RedDevil; 07-05-2021 at 10:10 AM..
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