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Gator_Man · Posted: Wed Feb 23, 2005 6:24 pm Post subject: correct prop

the original prop on my boat allowes the engine to over-rev. i dont know what size it was / it wasn't stamped. dealer in smithfield told me to start with a 17 pitch. it will over-rev even worse now and has slowed down even more. i have to drive by the tach so i dont go past 5200rpm. anyone know what direction i should go with the pitch?( 15 or 21...) Question

RoughandReady · MOD Joined: May 17, 2004 Posts: 1018

Gator_Man · Posted: Wed Feb 23, 2005 7:32 pm Post subject:

thanks.
i thought the way to go was higher but wanted someone to comfirm before i spent the money.

Capt_Dave · Posted: Wed Feb 23, 2005 7:39 pm Post subject:

PROP PITCH EDUCATION 101
WHAT PITCH PROP DO I NEED?

EFFECT OF PROP PITCH ON RPM
A pitch change can increase to decrease the RPM's and bring RPM's into the recommended range
A 2" INCREASE in pitch (For example from a 21pitch to a 23pitch) Typically results in a
DECREASE of approximately 300-400 RPM.

FIRST, DETERMINE MANUFACTURES RECOMMENDED RPM
Find the manufacture's recommended RPM range in the owner's manual or ask your dealer

TEST FOR MAXIMUM RPM
Using the existing propeller or a new propeller, make test runs to determine the maximum RPM
and boat speed. Vary the trim angle for optimum performance.

RPM HIGHER THAN RECOMMENDED
If the actual WOT RPM's are ABOVE the recommended RPM range, install the next LARGER
pitch propeller to DECREASE your WOT RPM. Re-test the WOT RPM.

RPM LOWER THAN RECOMMENDED
If the actual WOT RPM range is BELOW the recommended range, install the next SMALLER pitch
propeller to INCREASE your WOT RPM. Re-test the WOT RPM.

When you combine all these factors, you have the information you need to select the correct
propeller for maximum performance, safety, and fuel efficiency.

Gator_Man · Posted: Wed Feb 23, 2005 8:22 pm Post subject:

now i know. thanks. that was exactly the information i was lookin'. thanks to both of ya.

Libertas · Deck Hand Joined: Mar 21, 2005 Posts: 9

One important additional point. The cup can be as important as the pitch. I lowered the pitch on my props because I could not reach above 4300 RPM to get to the right place in the efficiency curve. I actually got some "burn" on the props from the friction not to mention really lousy performance. I took the props back and they added cup with the same lower pitch and I added speed and 15% better gas mileage than the original settings.

PS


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