What is the correct prop

[JREUREKA]

I have a 1986 17' bowrider with a 140 hp mercruiser alpha 1...when i purchased the boad new, the saleman traded the original prop for one intended for high altitude operations..most of my boating is 6500' or higher...the prop was perfect, but last year the prop got damaged and i took it in for rebuild but did not get the same prop back...the one i received just does not measure up..i purchased a new prop 15.5" x 13" pitch, but the boat does not plane as quick as it should and sometimes hangs...which direction in pitch do i need to go to get the boat to plane quicker like it used to???any one got any good information...getting frustrated, and can't keep buying props that don't work...please help...

 

[Bondo]

Re: What is the correct prop

but the boat does not plane as quick as it should and sometimes hangs...which direction in pitch do i need to go to get the boat to plane quicker like it used to???

Ayuh,.... Smaller pitch equates to more Power...
But, I never knew there was a 13" pitch available,...
Maybe have to go smaller diameter as well...

Has the motor been retuned for Hi-altitude runnin',..??

 

[steelespike]

Re: What is the correct prop

What makes you say you didn't get the right prop back?
At 6500 you lose about 19-20% of power; even if properly tuned for the height.
What rpm does it reach on plane? In my opinion a 13 should jump on plane not run real fast but jump up.I think you have other issues.At that elevation you run real rich ;you could have a fouled plug(s)Perhaps the foam under the floor has absorbed water,throttle not opening all the way.

 

[JREUREKA]

Re: What is the correct prop

They just traded my prop with one they had already rebuilt..Said it was the same, but when I installed it on the outdrive, the diameter was larger than the original..the one they traded me is 16"...It fit ok and I tryed it out prior to buying the new 15.5" x 13"...Hole shot was decent but engine RPM just did not match speed(almost sounds and acts as when you have the outdrive trimmed way up, alot of revs)...This is the only change to the boat and performance is just not close to the same as the one I traded where hole shot was great even loaded and top end was also very good...Motor is running excellent... I guess my question is this...could it be I need more pitch and less diameter???

 

[JREUREKA]

Re: What is the correct prop

Ayuh,.... Smaller pitch equates to more Power...
But, I never knew there was a 13" pitch available,...
Maybe have to go smaller diameter as well...

Has the motor been retuned for Hi-altitude runnin',..??

Nothing has changed on the motor and always have used at higher altitudes...only difference is prop..I guess I am alittle frustrated...The saleman when I purchased the boat new said "quote" you'll need this prop to run in utahs altitudes(and it was perfect)...Now I can't find anyone that knows what that might have been or what the orignal props were for that particular engine, outdrive, boat size, back in 1986..As everyone knows, its expensive to keep buying props at $135.00 a pop just to try them out, but I'm not giving up just yet...I know that prop is out there somewhere>>>

 

[steelespike]

Re: What is the correct prop

Generally diameter is a secondary consideration, only in the extreme 3/4 inch or more.
Suddenly dawns on me you haven't mentioned rpm or speed when planed.
I just checked here at Iboats and almost without exception 14",13".12" on down are 16" diameter Typically 15 on up are under 16.I think you need at least a 15. But the planed rpm and speed will tell. without that its a real crap shoot.
At sea level; if a 3.0 140 runs say a 20" pitch (just for even numbers)a 20-% reduction would put it at a 15" pitch. Using a 20% power loss to figure prop reduction.
You shouldn't run without a tach.Especially an I/O.

 

[elkhunter338]

Re: What is the correct prop

You could buy an adjustable prop. i have one from WestMarine and so far I like it. Been running it for 5 years. Also I thin Pirahna has a prop with replaceable pitch blades.
Just a thought.