[PSUBS-MAILIST] prop size

Marc de Piolenc piolenc at archivale.com
Thu Sep 5 18:25:55 EDT 2013


On 9/6/2013 1:34 AM, JimToddPsub at aol.com wrote:
> Hi Marc,
> I think the premise is that for a /given power input/, a larger diameter
> prop is going to /result/ in a lower RPM, not that there is an inherent
> advantage in lower RPM within the scope of the question.

If the pitch is kept the same, then that's true. Otherwise, up to the 
cavitation limit, speed is an independent variable. And for the reason I 
gave it is advantageous to keep it higher rather than lower. Of course, 
at some point you will encounter diminishing returns, where the power 
saved by reducing swirl is eaten up in additional friction drag.

Calculate, calculate, calculate...

Best,
Marc
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