When Alexander Graham Bell was in the process of developing a flying machine, he quipped to his wife that there should be no difference between the thrust of a propeller in air or water. His wife replied that "you can row a boat in water with an oar but you can't row a flying machine in the air". Thus, Bell didn't pursue that angle. But I think he was right.
The question is, can anyone with a good familiarity with fluid dynamics state with any certainty whether it is true that for a given amount of thrust, the power required is the same whether a propeller be in water or air? Let us set aside all questions of density variation due to temperature and assume standard conditions obtain. To put it another way, is the power required per pound of thrust essentially the same regardless of the medium, assuming a properly-designed propeller?
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