What pitch prop should I get?

rtclaus

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May 4, 2015
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I have a 92 Blue Fin Spectrum 1750 with a 3.0 mercruiser alpha one stern drive. WOT I get just under 33 mph @ 5000 rpm with 32 gal fuel, 2 people and a Boxer on board according to my fish finder. I want to get some more top end speed, I currently have a 15x17 aluminium 3 blade. Would I get much of an increase going to a 19 or 21 or am I better off staying with what I have? Thanks for any help
 

bobdec

Petty Officer 2nd Class
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Aug 12, 2010
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170
Believe you 3.0 is 135 HP at 4800 RPM, if so you are a bit under pitched at 5000 WOT. Rule of thumb is 200 RPM per inch of pitch. You are so close that maybe a more SS performance prop in same size may buy what you need. A 19 will drop your WOT to 4600 RPM that's to much and theoretical 20 (hard to find) would be perfect. Backside or more pitch (think higher gearing in a car) is a slower take off. It may slow your hole slot and extend planing time.
 

rallyart

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Jun 7, 2008
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1,175
A 19" Stainless prop will likely get your speed maxed out and put the RPM in a better range for your engine. Is your current prop worn? That can cause the engine to rev higher as there is not as much bite. You want to get your RPM down to 4800 or a bit lower when you run at full throttle.
 

rtclaus

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May 4, 2015
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How much over an increase do you think I would get with a 19 stainless? My prop doesn't appear to be in bad shape only a few nicks.
 

steelespike

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Apr 26, 2002
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19,069
Is the motor in excellent tune?Bottom clean and smooth?
Typically a setup like yours would over rev excessively with a 17" prop.
The 17 would usually be used for water sports with a load of people.
Before making any suggestion we need to confirm the numbers.
Is the speed by gps through your fish finder?Your slip is 18% at 5000 rpm, a little high.
Slip numbers that are off can usually be traced to the the speedometer or the tach
How is the performance ? Should have a strong hole shot with the 17" prop.
Your boat should be able to handle a 21" prop.Hole shot probably a little sluggish but top speed around 40.
Problem is from your numbers I don't think it could do a 21" prop
If you can varify your tach and get a gps speed that would help.
You could throw a 19" prop on there and "possibly" gain a little speed at the sacrifice of some hole shot and load handling.
 

rtclaus

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May 4, 2015
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Yes speed is through my gps on Humminbird 859. Motor was just tuned up. Yes hole shot is strong, performance is good, I have no complaints would just like more speed. I guess I will go with a 19. Never had to buy a prop before does anyone have any recommendations as far as brand ? I think I will stay with aluminum. Thanks for all the help from everyone !!
 

SkiDad

Lieutenant Commander
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Jul 18, 2010
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i have a Turning Point Hustler aluminum that will outrun my stainless prop for top end. They are cheap enough too - you also need the hub kit. It's the best looking aluminum prop i've seen. In my experience with one in the same pitch it was 2 mph faster. LOTS of bow lift, and I think they run like the next pitch up. So keep that in mind with this brand that a 17 might be your best pick.

I also like Michigan Match props - a good solid prop for a good price - you can get those in exact replacements and don't need a hub kit on most. Maybe a 14x19 is the way to go with this brand? http://boatpropellers.iboats.com/Me..._031025_Propeller/437/1158/?cart_id=075675370

i wouldn't expect miracles with prop - maybe you will go up about 2-4 mph but that is about all. In your case it seems like you should be getting closer to 40 MPH with that light of a boat, so I'm not sure what gives.
 

steelespike

Supreme Mariner
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Apr 26, 2002
Messages
19,069
I agree with SkiDad the Turning point Hustler is a great prop and iboats is having a sale it appears it includes the hub.
I also agree the Hustler acts like a a pitch higher. So it would be good to stick with the 17" it appears it will act like a 18.
With the bow lift it should help top end.
You might check that the timing is set right and advancing as it should.It may be electronic but still good to check.
Check that the throttle opens all the way.
 
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