Prop selection for Mercruiser - Updated

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freak007

Petty Officer 2nd Class
Joined
Jul 19, 2008
Messages
126
Boat - 1984 Rinker V170, 16.5' Bowrider - 1700 pounds dry, typical weight is 2700 or 2500 + a tuber or occasional skier

Engine - 120Hp 2.5L Mercruiser I/O, 3900-4300 WOT

Drive - Alpha 1, 1.94 ratio

Props Tested (both aluminum 3 blade)-
(Michigan?) SMC 380-CUP = 15 1/4 x 21 with a 3* (?) aft rake in good condition
Black Max 48-78-118-17 = 14 1/2 x 17 with a 16* (?) rake in fair condition (some small nicks)

Results -
  1. 4000 RPM @ 2100 pounds with the 15 1/4 x 21
  2. 4150 RPMS @ 2100 pounds with the 14 1/4 x 17
  3. 4000 RPMS @ 2100 + a tuber with the 14 1/4 x 17
  4. 4100 RPMS @ 2500 with the 14 1/4 x 17
All speeds were with the trim max up for maximum RPM. I do not have any speed data because my speedometer quit working.


I am looking for the ideal prop for my "typical" load and use... It looks like the 17 will be acceptable for my goals... but it just seems that it should do better... I want a better holeshot without sacrificing too much in the midrange... due to the *****ty man-made lakes nearest to where I live, I would like to stick with an aluminum prop...

I was looking at the aluminum 15 X 16 4 blade Vortex...

Any advise?
 
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freak007

Petty Officer 2nd Class
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Jul 19, 2008
Messages
126
Re: Prop selection for Mercruiser

Re: Prop selection for Mercruiser

not my boat... but it is the same model so it gives a good idea as to the hull I am working with:

1777517_1.jpg
 
Tail_Gunner

Tail_Gunner

Admiral
Joined
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Messages
6,237
Re: Prop selection for Mercruiser

Re: Prop selection for Mercruiser

Results -
  1. 4000 RPM @ 2100 pounds with the 15 1/4 x 21
  2. 4150 RPMS @ 2100 pounds with the 14 1/4 x 17
  3. 4000 RPMS @ 2100 + a tuber with the 14 1/4 x 17
  4. 4100 RPMS @ 2500 with the 14 1/4 x 17
:D............:rolleyes: ........Yout tach is off.

4 inches of pitch and 100 rpm decrease...:redface:
 
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freak007

Petty Officer 2nd Class
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Messages
126
Re: Prop selection for Mercruiser

Re: Prop selection for Mercruiser

Tail_Gunner said:
Results -
  1. 4000 RPM @ 2100 pounds with the 15 1/4 x 21
  2. 4150 RPMS @ 2100 pounds with the 14 1/4 x 17
  3. 4000 RPMS @ 2100 + a tuber with the 14 1/4 x 17
  4. 4100 RPMS @ 2500 with the 14 1/4 x 17
:D............:rolleyes: ........Yout tach is off.

4 inches of pitch and 100 rpm decrease...:redface:
Click to expand...


Tach was confirmed accurate a week ago... I checked it against my Snap-On timing light... I will be going out again today... So I will double check it again
 
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freak007

Petty Officer 2nd Class
Joined
Jul 19, 2008
Messages
126
Re: Prop selection for Mercruiser

Re: Prop selection for Mercruiser

and the results are in... my factory tach is accurate to ~2500 RPM (where I stopped checking last week)... New results with the Black Max (14 1/2 x 17 with a 16* rake), Tach reading was from my Snap-On timing light
  1. 4310 RPM @ 2250 pounds (lightest "normal" weight)
  2. 4150 RPM @ 2650 pounds
  3. 3950 RPM @ 2450 pounds + a tuber

Hole shot was weaker than I would have liked... There was also a fair amount of chop on the lake, so the engine was kept trimmed all the way in. If I tried to trim it out it would ventilate really bad (that was not an issue yesterday when the lake was as smooth as glass). The prop is also more tore up than I thought... one blade has a small crack in the edge as well as is visibly bent (does not have the same rake as the other two)...

I am thinking that once I install the Smart tabs that I could actually stand to go up to a 18 or 19 pitch prop, as long as it will hold well enough to allow me to trim it out... Maybe a 18 pitch 4 blade for tubing/sking and a 20 pitch 3 blade for cruising?

Or do you think I should install the smart tabs and have the current prop repaired... then test again?
 
Tail_Gunner

Tail_Gunner

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Re: Prop selection for Mercruiser - Updated

Find a prop that will take your max rpm to 4600
 
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freak007

Petty Officer 2nd Class
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Messages
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Re: Prop selection for Mercruiser - Updated

why 4600? Everything I havw seen for this engine says 3900-4300
 
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freak007

Petty Officer 2nd Class
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Messages
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Re: Prop selection for Mercruiser - Updated 20 SEP 08

Re: Prop selection for Mercruiser - Updated 20 SEP 08

Ok, one more update... I had the Black Max rebuilt, and purchased an alumimum Hustler 15-1/4 X 15 as well...

1) 4300 RPMS @ 2500 with the 14 1/4 x 17 Black Max

2) 3900 RPMS @ 2250 + 250 skier with the 14 1/4 x 17 Black Max

3) 4100 RPMS @ 2300 + 200 tuber with the 14 1/4 x 17 Black Max (looses RPMs BAD in tight turns)

4) Overev @ 2250 with the Hustler 15-1/4 X 15 (kissed 4600 and backed out)

5) 4500 @ 2250 + 200 tuber with the Hustler 15-1/4 X 15 (holds 4300 even in the tightest turns)


I LOVE the holeshot of the Hustler, it also holds better in the corners, but top speed (on dream-o-meter) is 27 MPH VS 32 for the Black Max... The Black Max will pull me (180 lbs) up easily (under 3 seconds) when I ski (deep water start), but struggles a bit with my Dad (250 lbs)... Hustler is MUCH more fun to tube behind...


I am ready to purchase one more prop, and I want the best of both worlds. Money is not an issue... The ideal prop would pull like the Hustler, but have the top speed of the Black Max (or higher :D)... I know that is a tough bill to fill, but if it can be done (perhaps a shifting prop of some sort) I would be really happy :D
 
nlain

nlain

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2,445
Re: Prop selection for Mercruiser - Updated

If you want to stay with Turning Point (Hustler) contact them and explain what you have done and what you would like to have, they seem to be real good people, that way you could swap props on the same hub. I bought one of their props and it performed well with the exception of WOT, I contacted them they swapped for a $20.00 fee, (freight) I returned the original, sent email the day after UPS said it arrived to see when the replacement would ship out, they had shipped out the same day original had arrived.
 
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steelespike

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Joined
Apr 26, 2002
Messages
19,069
Re: Prop selection for Mercruiser - Updated

I would go with the Hustler in a 17.Should put you at about 4300 still good hole shot and maintain that good grip.
 
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freak007

Petty Officer 2nd Class
Joined
Jul 19, 2008
Messages
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Re: Prop selection for Mercruiser - Updated

Will I have a big improvement going to SS??

When I say "money is not an issue" I mean that it REALLY is not an issue... the boat may be an 1984... but someone else is paying for the prop ;)
 
Tail_Gunner

Tail_Gunner

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Re: Prop selection for Mercruiser - Updated

freak007 said:
Will I have a big improvement going to SS??

When I say "money is not an issue" I mean that it REALLY is not an issue... the boat may be an 1984... but someone else is paying for the prop ;)
Click to expand...


Yes SS is superior to alum, less deformation under high stress along with a thinnner blade allowing for more pitch..aka under high speed a alum prop will deform if thats the right word.... it also allows the designer to create a blade with more gripping potential cupping etc due to the nature of its strength
 
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freak007

Petty Officer 2nd Class
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Jul 19, 2008
Messages
126
Re: Prop selection for Mercruiser - Updated

So a 14-1/4 X 17 Turning Point Express is the recommendation?
 
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