Prop Pitch??

[98srx6]

1) Performance issue you are trying to correct.
-Looking to increase max RPM's to 5500. Also looking to eliminate ventilation in corners and increase out of the hole performance for getting skiers up, etc.

2) Current prop manufacturer, model, aluminum or stainless and as a minimum.
-Unsure of manufacturer and the model # is 176214. It is a 3-Blade aluminum prop.

3) Current prop diameter and pitch (required).
-14x17

4) Wide open throttle RPM and speed with an average load (very helpful)
-4900-5000 RPM. 38 MPH (using the boats speedo)

5) Engine/drive make, model, year, and HP
-1989 Evinrude 90hp V-4 VRO.

6) Boat make model, year, length and weight
-1989 Rinker V-170. "This outboard runabout (bowrider) is 16.5 feet long and weighs 975 (pounds dry). This weight does not account for passengers, fuel, or gear. The beam of this craft is 86 inches."

7) Trim Tabs
-Nauticus SX Smart Tabs Model Part # SX9510-40 w/ pressure adjustment setting in the center.

 

[Bifflefan]

Re: Prop Pitch??

Sounds almost like my boat.
I have a 16' Starcraft American with an 85 HP Johny. only i have a 13x17 prop and run about the same speed. I have no trouble pulling a tube with 4 people on it and 4 in the boat. You can drop down -2p that will help the RPM's and pulling. But id see about getting a 13x prop. I like it better than the 14x i had on.

there is a guy on here that really can help as he has the formula for the correct calcs. Im sure he will post something soon.

 

[hwsiii]

Re: Prop Pitch??

98, you are showing a prop slip of 6% right now and that is lower than I would normally expect for an aluminum prop, but that is good. If you change the pitch to a 15" pitch in the same make and model of prop you have now it will increase your RPM by about 600 RPM and you should lose very little speed, but your hole shot and acceleration will increase very well. Here are my calculations.


Prop Slip

Prop Change

H

 

[98srx6]

Re: Prop Pitch??

Would using this Solex prop be a shot in the dark as far as how it will perform compared to the 15P version of my current prop (link below). I really like the idea of the rubber hub as the lake that I operate this boat in has alot of submerged stumps, deadheads, etc. If your opinion is that the OMC prop would be best, then that is what I am going to use.
(Solex Prop 15P)

Thank you very much for your expert advice!

Current Prop OMC 17P

Proposed Prop OMC 15P

 

[hwsiii]

Re: Prop Pitch??

I don't really understand the question, because both the Solex and the OMC props have rubber inserts for protection when hitting something.


H

 

[98srx6]

Re: Prop Pitch??

After re-reading my last post, I don't think I understand the question either, but you answered it.

Is this the correct prop that you are recommending? Does the 1/2" difference in diameter have any effect on performance? Sorry for all of the questions.

Thanks again for your help.

 

[hwsiii]

Re: Prop Pitch??

98, my mistake. I can't tell you how the boat will react to the change from the OMC to the Solex, but you should gain RPM and a better hole shot. I do not know the blade geometry of the Solex versus the OMC, if I did I could tell you how it should do compared to the OMC. The one big advantage it has is that if you hit something and spin the hub all you have to do is carry a spare hub and you an fix it right then and there instead of having to bring it to a prop shop to have a new hub installed, and if you decide to sell it later all that has to be done is to change the hub and it will fit a wide variety of motors. As far as having a larger diameter that will give you more blade surface area which will help with prop slip when you are trying to pull a skier up. The ventilating in corners may not be helped much that is hard to say.


H

 

[98srx6]

Re: Prop Pitch??

This is probably unrelated to the prop questions, but if I am still getting bad ventilation in the corners after replacing the prop, should I try to lower the motor down a notch? The cavitation plate is currently almost 2" above the keel.

 

[hwsiii]

Re: Prop Pitch??

Most certainly you should, these are aluminum props without much cup in them or blade geometry and that is why they are ventilating.


H

 

[98srx6]

Re: Prop Pitch??

Are there any aluminum props with more cupping and better geometry that may yield good results or should I just drop the motor down and use the same make and model prop that I am currently using (just in a 15P prop instead)?

How about a 4-blade prop?

 

[hwsiii]

Re: Prop Pitch??

Ok, here is my recommendation for you a better prop for your needs.


Price: $87.99
You Save: $76.01
Compare: $164.00
Discount: 46.4% Off
Add Hustler Aluminum Propeller Prop: H2-1315 Hub: 33 To Your Cart

Propeller Specifications:
SKUrop #H2-1315Hub #33
Manufacturer: Turning Point
Brand: Hustler
Material: Aluminum
Diameter: 13 - 3/4?
Pitch: 15?
Blades: 3
Rotation: Standard (Clockwise)
Usually Ships Within: 1 Business Day

This particular aluminum prop is very aggressive and has cup on the trailing edge which will theoretically stop your ventilation in the corners and it also will help to pick the bow of the boat up and you probably won't lose much speed.


H

 

[98srx6]

Re: Prop Pitch??

Results: I purchased the Turning Point Legacy prop shown at the link below in a 15P.

Link

Results are as follows.

Max RPM: 5200-5300 RPM
Max Speed: 36 MPH

Holeshot has improved greatly as has the ventilation in the corners (still a little bit of ventilation, but it is very tolerable).

This is not a vented prop and there does seem to be a bit more ventilation then there was with the old prop when accelerating from a dead stop. Not sure if this is to be expected with the more aggressive geometry, or if I should be lowering my motor one notch. If I do lower the outboard, is there a rule of thumb as to how much RPM I will lose or is it trial and error due to different hull designs?

Overall this prop was a big improvement, thanks for your help hwsiii!

 

[hwsiii]

Re: Prop Pitch??

98, yes you an expet a lot more ventilation at holeshot beause of the aggressive nature of the prop, so it an get up to speed. Yes also if you lower it one noth you will probably lose about 100 RPM.
I amglad it is better than what you had.


H

 

[98srx6]

Re: Prop Pitch??

hwsiii,

Would I be able to trouble you to check my prop slip with the new prop installed. If you would like I can update your required form with my new prop info and all of the boat info. Thank you!

 

[hwsiii]

Re: Prop Pitch??

Your prop slip is now at 3%.


H

 

[98srx6]

Re: Prop Pitch??

Your prop slip is now at 3%.


H

Is this number realistic or is it likely skewed because I used the boats built in speedo? Is the boats speedo always skewed a certain way or could it be above or below the actual boat speed?

 

[hwsiii]

Re: Prop Pitch??

No, the number is not realistic, use a GPS and run the boat in 180 degree opposite directions to discount any tidal or wind interferences, then add the two numbers together and divide by 2 to get more realistic numbers. But every prop is not really pitched at what the manufacturer claims so it will be off some. I have specific software I designed to show a much better representation of what the actual pitch of the prop is.


H

 

[98srx6]

Re: Prop Pitch??

Well, I finally got the boat out again this past weekend and ran a couple of tests. Results are as follows:

-35 mph (on GPS)
-4900-5000 RPM

 

[hwsiii]

Re: Prop Pitch??

98, your prop slip now shows it to be at less than 1% and that means the prop actually has more pitch than the 15" that TP states. But I have found the TP props to be very erratic when it comes to the pitches that they state for their props.




H

 

[98srx6]

Re: Prop Pitch??

Would you estimate the pitch to be somewhere in the 16-17" range?