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| Propeller sizing guru needed |
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gporter
Member
Username: gporter
Post Number: 11
Registered: 03-2006
| | Posted on Tuesday, January 27, 2015 - 03:20 pm: | 
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If I have two props each of which allows the engine to run at rated RPM, but with different diameters and pitch, which one is likely to be the most efficient? the high pitch lower diameter or the opposite?
And which one is likely to drive the boat at a higher speed?
Thanks
Gene Porter, in NH with 2' of new snow and more coming down |
jb_castagnos
Senior Member
Username: jb_castagnos
Post Number: 1004
Registered: 07-2002
| | Posted on Tuesday, January 27, 2015 - 07:26 pm: |
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Larger diameter props are usually good for slower moving heavy boats, smaller diameter higher pitch props are for planing boats and higher speeds. |
miro
Senior Member
Username: miro
Post Number: 791
Registered: 11-2001
| | Posted on Tuesday, February 03, 2015 - 06:10 pm: |
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If the engine can run the higher pitch prop at the same speed as the lower pitch prop, then that is the one that will go faster.
Your engine will producing more torque than for the smaller pitch prop, thus making more horsepower.
Horsepower is Torque x Speed
You'll also be using more fuel. But you'll be going faster.
To go at the same boat speed, you could reduce your engine speed ( RPM), this using less fuel.
Efficiency depends very much on the type of hull that you are driving.
However, propellers are an endless source of discussion and have been so for well over 150 years, since John Ericcson ( inventor of the Monitor gunboat in the Civil War) got a patent for his propeller in 1837 in Great Britain.
Miro |
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