Prop question I think.

M1sterh

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Joined
May 27, 2018
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5
2004 215 Weekender 5.0L 220 HP. I have the boat 3 years, came with a 14x19 SS prop on the boat. I'm maxing out at 4200 WOT pushing it to get up to 26 MPH. It used to go faster but the last month of so it slowed up. I used to cruise at 26 MPH and top speed of around 32.The engine's running good, just not moving like it was. I changed the prop to the original aluminum 15x17. I can now get 4800 RPM's at 28 MPH. harder to get on plane. 3500-4000 RPM's. With the SS prop getting on plane was a piece of cake, under 3000 RPM's.I feel with the aluminum 15x17 it's just pushing the engine too hard so I'm going back to the SS 14x19 for now. I'm stumped. any suggestions?
 

jimmbo

Supreme Mariner
Joined
May 24, 2004
Messages
12,944
I doubt you have 17" and 19" diameter props.
Has the boat been sitting in the water for a long period? If so, then you might have a growth issue.
Otherwise, what shape is the engine in? Compression, Spark? Timing advancing? Any work done to it recently where the throttle linkage was disturbed?
I will assume it is a carbed engine and probably has a WOT range of 4400 - 4800 rpm.
If a 15 X17 is overloading the engine a 14 X19 is not going to lighten it up
Your numbers were 4200 with the 19, then 4800 with the 17. The 19 is loading the engine more, hence the lower WOT rpm, which by the way, is below the minimum of 4400
 

M1sterh

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Joined
May 27, 2018
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No I don't have a 17" or 19" diameter. A senor moment. Boat hasn't been sitting long. I use it all the time. Compression, spark, timing is good. No work recently done. So with the 17 pitch I'm getting the right WOT rpm but the speed isn't there. To hard to get on plane and the engines seems to be working too hard. The 19 pitch which used to be fine WOT is too low and my top speed has significantly decreased.
 

jimmbo

Supreme Mariner
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May 24, 2004
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12,944
Is the timing advancing as the engine revs? Is the carb clean, no gum/varnish/dirt in the power and/or main circuits?
 

M1sterh

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May 27, 2018
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You think 17" SS will make that much difference opposed to the 17" aluminum. I need to get the speed up without being at WOT.
 

Sea Rider

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Sep 20, 2008
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12,345
If it used to work fine, why is it not working right right now ? Need to fully check the engine overall cond as seems is with hidden issues before going for other less pitch prop.

Happy Boating
 

M1sterh

Recruit
Joined
May 27, 2018
Messages
5
I pulled the boat out of the water. The bottom didn't look that bad, but heavy in some spots. It has been a hot summer. Power washed the bottom. Back to normal. 32.4 mph at 4800 rpm.
 

QBhoy

Fleet Admiral
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Mar 10, 2016
Messages
8,286
Agree with searider. This isn’t a prop issue I’d say. You are way down on performance no matter what.
 
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