Friday, March 5, 2010

Re: [Electric Boats] propellers

 

Welcome, Larry. 
 
Your expertise will be welcome.  You must have Dave Gerr's "Propeller Handbook" in your office.  It has a wealth of info about props.
 
It seems to me an electric drive is much easier to optimize than ICE as the power absorption of the prop is simple to measure (volts x amps = watts).  Watts vs. speed for various throttle positions measured in controlled (no wind or current) gives a good picture of efficiency.
 
Props are easy to change and motor rpm / prop rpm ratio with is easy to change with belt drive. Comparing watts vs. speed curves shows which prop / drive ratio is the best for a particular boat / motor setup.
 
I bet a large diameter, high aspect ratio 2 blade prop would give excellent performance as a sail aux drive, especially if a method could be devised to lock the prop in the vertical position hiding in the wake of the skeg.  A folding prop that would work in reverse would be even better.
 
Denny Wolfe
 

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