Prop Change/What can I Expect

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a1nowell

Chief Petty Officer
Joined
May 12, 2009
Messages
437
I have a 1984, 24', JC Tritoon powered by a Mercruiser 470. My prop is currently a SS 14" diameter X 19 degree pitch. I had the boat out yesterday and by GPS it was running 25.5 MPH by GPS at 2750 RPM. It has been suggested that I go to a 16" diameter prop with a 15 degree pitch. If I do this what may I expect in MPH and RPM?
 
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Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: Prop Change/What can I Expect

Lets start at the begining. Pitch is measured in inches, not degrees. Rake is measured in degrees and may play a part in prop decision down the road. However, if you're at only 2750 (wide open, trimmed) now we may be looking at a motor issue rather than a prop issue. We're looking for almost 2000 rpm which is a lot for a prop only issue. Which outdrive / gear ratio do you have?
 
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a1nowell

Chief Petty Officer
Joined
May 12, 2009
Messages
437
Re: Prop Change/What can I Expect

I have never had the motor at WOT. The 2750 RPM is maybe 60-70% of WOT.
 
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sethjon

Senior Chief Petty Officer
Joined
Jun 8, 2010
Messages
692
Re: Prop Change/What can I Expect

a1nowell said:
I have never had the motor at WOT. The 2750 RPM is maybe 60-70% of WOT.
Click to expand...

You need to know WOT first so that when you make a change it won't be too much and possibly blow the engine.
 
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steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: Prop Change/What can I Expect

We need your wot rpm and speed to tell where you are at.
 
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