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Mfitzdmax

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Posts: 27
Reply with quote  #1 
Ive been banging my head against a wall trying to figure out the correct prop. Im currently running a Powertech ptz17p. Im on the third hole down from the top. My rpms are at 5350 and speed is around 44.5. My last prop was an Apollo stainless 17p, when i ran this prop on the second hole down somehow i was getting a negative slip%. 5150 rpm's and 45.6 MPH. Thats roughly -2.5% slip. Not possible.  Could the emm be giving false readings on my rpms. I use the NMEA on my graph for speed and RPM. What prop diameter do these etec motors like on deep v boats. My boat is a Alumacraft Trophy 175. Has anyone had much luck with the Viper props? Im thinking about going down to a 16p Powertech or 16p Viper.  
PhilH12

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Reply with quote  #2 
Where is your AV plate running on plane and trimmed?  Should be above solid water and getting splashed.

Don't chase props until the engine height is correct, but you may pick up some rpm's when it's right.  Yours do sound a bit low without looking at an Optimum RPM chart.

Phil

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Huey

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Reply with quote  #3 
Viper are good props on the right hull and a 16 inch will get you into the sweet spot of 5500-5700RPM for the 2.6L G1 V6. As Phil said though if you can not see the AV plate when trimmed correctly you are too low. Hole no.3 is where I have rigged most G1 over the years, but every hull is different.
Mfitzdmax

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Reply with quote  #4 
Quote:
Originally Posted by Huey
Viper are good props on the right hull and a 16 inch will get you into the sweet spot of 5500-5700RPM for the 2.6L G1 V6. As Phil said though if you can not see the AV plate when trimmed correctly you are too low. Hole no.3 is where I have rigged most G1 over the years, but every hull is different.


Im on hole 3 now, but the last 2 props i have not been able to get much trim out of the motor before i feel some ventilation or cavitation for some reason. The av plate is right where it should be. My one transducer is mounted below the hull i am getting a big spray from it to the motor. Im wondering if that is causing the cavitation or ventilation.
Huey

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Reply with quote  #5 
Could be but one thing for sure, all that water being sprayed up on the outboard is what that engine is breathing and that is not good. Get a spray deflector to stop the spary hitting the engine.
steelhead

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Reply with quote  #6 

Evinrude in their motor installation manuals state no transom or hull mounted devices within 12" either side of gear case. 

Causes aerated cooling water >overheating.
Loss of prop bite thus loss of mpg, holeshot and poor high speed handling especially trimmed out to the ragged edge.

Manuf's prop pitch #s are an imprecise calculation but close enough of predicted pitch to compare different brand and models of props.  Too many variables, blade size, rake, skew, type and amount of cupping and where the cupping is located tip and/or trailing edge.  Most modern props are a progressive pitch design, so pitch changes from prop hub blade root to blade tip.

Only way to dial in owner's handling desires for each boat hull type is trial and error, much of final owner's decision is subjective

Propping for optimum rpms range gives the best loading characteristics on the motor, longest lowest engine wear life, usually best mpg.

https://www.miwheel.com/resources/terms/

rideoutr

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Reply with quote  #7 
Mfitzdmax, could you post your model #, also there is a bit of a difference between the '07 engine and the '08 engine. If memory serves me the '07 had a max rpm of 5500 and the '08 was closer to 5750. Your model # will have the model year.

Rick

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