Prop pitch selection question on a 30hp Johnson

[Johny25]

Ok my boat is a 14ft Lowe V hull with an 88' 30hp Johnson. I tested 3 props with my new Tiny Tach today and here are my results. I run with what I will call a heavy load 25% of the time and a light load 75% of the time. When the wife and second son go out with us is the heavy load, about 250 lbs heavier than the light load (that includes the 2 extra seats I have to put in the boat). Engine specs are 5200-5800 RPM at WOT.

10X13 aluminum OMC prop
Heavy load (gross weight 1,150 lbs) =5450 RPM at WOT
Light load (gross weight 900lbs) = 5700 RPM at WOT

10.5X11 aluminum OMC prop
Heavy load =6010 RPM at WOT
(didn't even bother with light load due to high RPM at heavy)

10.13X11 stainless steel Cabela's (brand new ugh...)
Heavy load =6290 RPM at WOT
(didn't bother with light load again)

Yeah I am bummed that the new SS prop is not gonna work at all. Have to sell it now, or trade it hopefully since my return time has expired. Not even 30 minutes on the prop . So I want a stainless prop because the stainless had much better performance characteristics than the aluminum. I know some say it doesn't matter with HP like this but I will disagree from what I saw and felt first hand.

So the question I have is since the same pitch SS prop ran almost 300 RPM higher than the aluminum prop could I actually push a 15 pitch stainless and be about 5500 RPM with a heavy load? Or should I go with the 14 pitch? I do not want to buy another $175-200 dollar prop that either over revs or under revs lol.

Cabela's does not have anymore props that fit my motor either so I am looking at a Solas stainless prop now. Does anyone own these and are they as good of quality as the Cabela's high performance props?

 

[steelespike]

Re: Prop pitch selection question on a 30hp Johnson

Excellent info but without gps speed we can't evaluate your setup.
It appears to me that a 13 is very likely the right prop.
You have a couple of ways to go A good prop shop can add some pitch to your ss prop.
It appears 2" could add or subtract about 300 rpm.Usually they can make changes up to about 2"
As you said you could sell or trade.Perhaps if you cry on Cabellas shoulder with what is essentially a new prop to exchange
maybe they would take pitty.
Read up on the Turning Point Rascal and Hustler props. they are an aluminum prop with close to ss performance.
at about 1/3 the cost of of ss. I believe the Rascal is for smaller outboards like yours.

 

[Silvertip]

Re: Prop pitch selection question on a 30hp Johnson

You saw an rpm increase -- you didn't see a performance increase. Props with identical diameter and pitch from two different manufacturers can and generally do perform differently. It's called "design". So not only did you change material, you changed manufacturers. So the difference in rpm is due in part to design, and some due to material. Can you say crap shoot when propping an engine??? Any actual performance gain from stainless will be minimal on that low hp engine.

 

[Johny25]

Re: Prop pitch selection question on a 30hp Johnson

The concern I have steelspike is that I buy a 13 pitch stainless and I'm at or above 6000 RPM again. The aluminum 13 seems to fit exactly in the RPM range but the way I see it is if I can turn a 15 in stainless then I can get better top end possibly. I don't have GPS and don't plan on getting one this year, the wife has had enough of me spending money on my boat for awhile (just got a minn kota ipilot bowmount

Hey Silvertip, an RPM increase (stainless) with the same pitch would indicate better performance, would it not? Or am I missing something here? I know it may seem like a crap shoot but it wasn't. The motor came with the aluminum 11pitch, I have done that stupid prop wizard calculator about 50 times and it continues to tell me to run an 10 to 11 pitch in stainless or aluminum. I understand different manufacturer argument but OMC does not sell SS props that I know of. So I had to start somewhere and the Cabela's SS prop was reasonably priced. And even a minimal gain can add up. Say I get 1.5 mph more with a stainless at the same RPM and pitch, what does that add up to fuel savings wise over 5 years?

Thanks for the advice guys, have any of you ran those solas saturn props?

 

[dazk14]

Re: Prop pitch selection question on a 30hp Johnson

Yes, we have put Solas saturns on small boats 10HP, up. They work much better than the stock pros. We've found, they tend to carry a little more pitch than a std uncupped prop. They have nice thin blades and adequate cupping, little rake and not as sophisticated a design as turning point props. Hard to beat the price for a stainless prop.

If you go to the turning point prop website, they have a calculator to determine prop matches. Lots of modern prop design, for short money. I believe you can exchange the prop if it doesn't work properly.

Do you have, or can borrow a car gps? I believe they all have a screen that indicates speed.

 

[steelespike]

Re: Prop pitch selection question on a 30hp Johnson

11" at 6290 assuming a 6% slip = about 28.6 Unfortunately slip is a guess.
You might be able to get a gps app for your cell phone.
An rpm increase should mean more speed but could mean more slip.

 

[Johny25]

Re: Prop pitch selection question on a 30hp Johnson

Hey good idea guys : ) My stepdaughter has one of those fancy smart phones and I believe it has a GPS app. I have just an ordinary flip phone and I can barely navigate it as is lol.... I will have to look at turning point props also : )

Oh and one of the reasons I am trying to get a prop that is most efficient for speed and RPM is I live next to a 25 mile long lake that also has a river system on both ends of it. It has beautiful mountain scenery and several old logging operations (I used to work for them operating tugs) and historical sites along it. And this year I want to be able to run the whole lake and river system with my family without it taking 2 days to do so. I didn't have enough HP last year but I do this year So if I can get 1-2 MPH more it can make a difference in time and fuel consumption.

 

[steelespike]

Re: Prop pitch selection question on a 30hp Johnson

To further complicate things I looked up 25 and 30 hp Evinrude etecs same basic motor direct injected.,same gear ratio.
Starcraft 16' 1032 lbs 12" al prop,5800@27.6,carolina skiff 1218lbs,12" al,5800 @ 28.3, Dragonfly,1184lbs,13" al 5975 @ 30.2.
Terrapin,900lbs,5900 @28.2.( 25 hp),Stump knocker 1142lbs,11",5725 @ 26.9, Alumacraft V16 968lbs,12"al 6000@ 31.6.
Just for fun(25hp) Sea Ark bass 1810lbs, 11"al,5385 @ 19.2.These motors are rated at 6000 but same gear ratio as yours.Note the biggest prop is a 13 and on the 2 boats closest to yours, Starcraft and Alumacraft ran 12" at 5800 and 6000 respectively.
I think you can see a 15 isn't likely to be ideal.If we had the gps speed we may be able to tell if you have slip or tach is high.
Is the anti vent plate( just above the prop) about even with the bottom of the transom?

 

[Johny25]

Re: Prop pitch selection question on a 30hp Johnson

Hey great info steelspike, you know I was starting to wonder if my tach was reading high. But when I put the SS prop on last and I got up to around 5900 RPM the boat didn't seem to really go any faster but the motor then revved 400 more RPM. I could hear it and feel that nothing was happening thrust. I mean I could tell the motor was over revving just by the sound of it.

I have the anti vent plate about a 1/2" below the bottom of the boat. This is the only position I could run the motor without it rooster tailing or spitting water all over the place. I tried it in 1/4" increments jacking it up to a height of 1.5 inches but it roostered and I had blowout issues in corners so I just put it all the way down on the transom and this is the only level it won't rooster tail.

Thank you for all the data lookup : ) I am going to get some GPS readings somehow now so you didn't do all that for nothing.

 

[steelespike]

Re: Prop pitch selection question on a 30hp Johnson

Does sound like bad slip or partial venting.
It'll be interesting if we can figure out this thing.

 

[Johny25]

Re: Prop pitch selection question on a 30hp Johnson

I think you are right that I probably can't run a 15 pitch with a heavy load. But 75% of the time I run with the 800-900lb load so I think I could maybe turn a 14 or 15 pitch SS at that load?

Now am I doing this correct by factoring everything in for total weight? Or are those calcs you put up minus boat and motor? Because I was really surprised that I hit almost 6300 RPM with the SS 11 pitch, and 6000 aluminum at the weight I had. The tach seems to be right on when idling and the 13 pitch seemed to have correct readings also. I could easily tell the two 11 pitch props had the motor over revving, just by sound of the motor alone.

It may take me a couple weeks to get the GPS readings and what not but I will finish this thread. I don't like dead end threads, especially when someone has invested their time to help : ) Thanks again guys for helping me!

 

[steelespike]

Re: Prop pitch selection question on a 30hp Johnson

When figuring weight its total; boat,motor,crew,and gear,Don't forget gas including tank if a steel portable, battery(s),trolling motor,oars,paddle "extra seats"
anchor.Heaviest I could find for your motor was 123lbs.
is the boat tiller or full remote steering?

 

[dazk14]

Re: Prop pitch selection question on a 30hp Johnson

To further complicate things I looked up 25 and 30 hp Evinrude etecs same basic motor direct injected.,same gear ratio.

Starcraft 16' 1032 lbs 12" al prop,5800@27.6,
carolina skiff 1218lbs,12" al,5800 @ 28.3,
Dragonfly,1184lbs,13" al 5975 @ 30.2.
Terrapin,900lbs,5900 @28.2.( 25 hp),
Stump knocker 1142lbs,11",5725 @ 26.9,
Alumacraft V16 968lbs,12"al 6000@ 31.6.
Just for fun(25hp) Sea Ark bass 1810lbs, 11"al,5385 @ 19.2.
These motors are rated at 6000 but same gear ratio as yours.

Note the biggest prop is a 13 and on the 2 boats closest to yours, Starcraft and Alumacraft ran 12" at 5800 and 6000 respectively.

I think you can see a 15 isn't likely to be ideal.If we had the gps speed we may be able to tell if you have slip or tach is high.

Is the anti vent plate( just above the prop) about even with the bottom of the transom?

Steelespike - please forgive the copyright infringement...

Fwiw- I asked out in the shop and we think the Cabelas prop may be a turning point express. We could be wrong...

But, I'd suggest contacting TP to verify and get the characteristics of the prop.

 

[Johny25]

Re: Prop pitch selection question on a 30hp Johnson

When figuring weight its total; boat,motor,crew,and gear,Don't forget gas including tank if a steel portable, battery(s),trolling motor,oars,paddle "extra seats"
anchor.Heaviest I could find for your motor was 123lbs.
is the boat tiller or full remote steering?

It is a tiller motor with electric start. With the SS prop on it she weighs in at almost 130lbs. I added a shift modification to it that gave it another couple pounds also so it is right about 130lbs. I added every single thing in my boat when I calculated weight : ) I even made my kids and wife get on the scale before we went out cause I didn't want the wife lying to me about her weight lol......

 

[Johny25]

Re: Prop pitch selection question on a 30hp Johnson

The more I think about it, the more I believe that I am going to buy a solas 10X14. I really think this will land me at about 5500-5600 RPM heavy load and 5700-5800 with a light load. I want to be on the high end of my recommended WOT RPM range when I run light. I think the 15 will put me within range but on the lower end, and I think a 13 pitch will put me over on the light and possible heavy load?

My theory is with the Stainless:
13 pitch will put me at 5800-5900 RPM heavy load light load 6000-6100
14 pitch 5500-5600 RPM heavy 5700-5800
15 pitch 5200-5300 RPM heavy 5400-5500

Now that I write it out like that the 15 doesn't look so bad lol...... Does this seem like a plausible estimation?

 

[steelespike]

Re: Prop pitch selection question on a 30hp Johnson

I think your numbers may be reasonable.I wouldn't be making any decision until you get some gps numbers to go with the rpm.
In the mean time you might chat with Turning Point as dazk suggests.

 

[Johny25]

Re: Prop pitch selection question on a 30hp Johnson

I am known for over thinking things steelspike lol....... I emailed Turning point yesterday, just waiting for a response from them now : )
And thank you dazk14 for the info : )

 

[Johny25]

Re: Prop pitch selection question on a 30hp Johnson

So turning point propellers emailed me back and said "no, we didn't supply Cabela's. Best regards" And that was all I got from them in response to an email that I asked many questions regarding their stainless props! I am a little miffed to say the least. Matter of fact I doubt I will buy any prop from them after an answer like that to a potential customer. I am going to give Mr. Liheng Chen a piece of my mind this evening about his **** poor customer service skills. I was going to ask where their props were made but Mr. Chen answered that by putting his name on the email lmao.......

 

[Johny25]

Re: Prop pitch selection question on a 30hp Johnson

Hey I talked to a highly recommended prop specialist today and he said he can cup my 11 pitch prop to lower the RPM by 800! This to me does not sound possible? I get that cupping a prop will lower RPM but can they really lower it that much? Just sounds unrealistic from what I understand.

 

[steelespike]

Re: Prop pitch selection question on a 30hp Johnson

Cup can be very effective there are cupped props that act like a 2 inch higher pitch.
800 seems extreme but you only need about 400-500.rpm.