Prop pitch selection question on a 30hp Johnson

[steelespike]

Re: Prop pitch selection question on a 30hp Johnson

Wow! An interesting development.
I'm on the edge of my seat.

 

[pootnic]

Re: Prop pitch selection question on a 30hp Johnson

I didn't go back through all the posts but did see your first one.
Why would you order a higher pitch stainless prop(14) then the 13 pitch aluminum that you already tried?
The 13 wasn't even at the top end of your recommended rpm range.

 

[Johny25]

Re: Prop pitch selection question on a 30hp Johnson

Ok Pootnic you are correct about the OP post with the 5700 rpm on the 13 aluminum. But those readings were on a windy day (raining). A few posts in I corrected it. I am running now at 5840-5850 in calm conditions. I expect the stainless to turn 50-100 RPM higher than the same pitch aluminum. If I am wrong, which may very well happen then the 14 pitch will be at about 5600 RPM. Which is still in the higher RPM range of my engine. The peak HP of the motor is at 5500 RPM. But I believe I can hit 5700-5750 with the 14 SS.

But all will be on hold anyway. My tach battery died today after 2hrs of total run time (I am not happy with that). And I developed a leak in my exhaust to powerhead gasket. Or it may be my crank case seal? I need to look at it tomorrow when I have more time, but at minimum I need to do the powerhead to exhaust seal

 

[1080tommy1]

Re: Prop pitch selection question on a 30hp Johnson

Started another thread and sorrry did not mean to hijack this one. You guys are great on this site and to me a wealth of knowledge can be gleened from these posts. I have to say, this is one of the most informative posts because of all the different scenarios you have gone through. Thanks again!

 

[Johny25]

Re: Prop pitch selection question on a 30hp Johnson

No worries tommy, you didn't hijack this thread. I will look for your thread so I can follow it: )

 

[Johny25]

Re: Prop pitch selection question on a 30hp Johnson

I will be updating this on Friday when my new tach arrives. Got my 14 SS yesterday and I also got a 15 pitch aluminum form another 30hp motor I bought. So I will best testing 3 props : )

 

[torbjorn]

Re: Prop pitch selection question on a 30hp Johnson

I will be updating this on Friday when my new tach arrives. Got my 14 SS yesterday and I also got a 15 pitch aluminum form another 30hp motor I bought. So I will best testing 3 props : )

Late response, sorry, but 6000 RPM is no problem for the 30/35. Simply run 25:1 Evinrude TC-W3 or synthetic oil above 6000. The 1984-2001 30/35 is geared .47, way lower than the .52 of the 1976-83 35. 14" pitch on your motor
is like 13" pitch on mine (1983). 15" pitch is far too much. A 'Cabella' 13" is in reality 12" pitch, I have one and checked
it on my pitch gauge. Best prop for you may be a Stiletto 10x14, it's in reality 13" pitch. Cupping too much will lower
the RPM and top speed, that's not the answer. If you cup, then jack the motor up. Should be at least 17.5" high
on the transom as shortshaft. In any case, I cup the Stiletto and 'Cabella' (Turbo) much more than stock, but
only out to max, diameter. I run a self-reworked Stiletto '10x14' on my 350 lb 14' Allison fishing boat, 41.7 mph @ 6050 RPM
but jacked up too high for your pleasure. I run Evinrude synthetic oil (XD-100) @ 37:1 just to be on the safe side.

 

[Johny25]

Re: Prop pitch selection question on a 30hp Johnson

Hey all good info torbjorn : ) Well my new tach is not here until tomorrow but I went and ran all 3 props and GPS them today because I was bored. Ok to start with I decided to make another jack plate, this time I raised the motor up 2 and 5/16". High as I figured I could get it without sucking air into the water pickup screen. And I ran the 14 SS, my GPS was 31.8 mph but I had to feather it because the prop was slipping. If I turned the throttle to fast it would slip bad. Also it was throwing water everywhere. So I took off the jackplate and ran all of them with the motor all the way down again : (

Here was my GPS results (without RPM data)

Heavy load at 1,100 lbs
10X13 stock aluminum 25.7-26.4 mph
10X14 Solas stainless 27.4-28.2 mph
10X15 stock aluminum 25.2-25.7 mph

Light load at 875lbs
10X13 stock aluminum 28.0-28.5 mph
10X14 Solas stainless 29.6-30.2 mph
10X15 stock aluminum 27.8-28.1 mph

I was really happy with how well the Solas stainless 10X14 performed, especially while loaded : ) and I was really surprised how bad the 15 pitch aluminum performed when light? The prop is in excellent shape but apparently was slipping really bad. I will get GPS and RPM next time out. And I really want to figure out my jackplate issue since it is worth almost another 2 mph!

 

[Johny25]

Re: Prop pitch selection question on a 30hp Johnson

I have heard a lot about an SS prop not being of any use on a smaller outboard and I can confidently say with the data I have that it is BS. The SS out performs the aluminum props hands down on all levels as I see it. Better hole shot, top speed and ability to plane at a lower RPM.

 

[1080tommy1]

Re: Prop pitch selection question on a 30hp Johnson

Those seem like great numbers off that ss prop. I am thinking about getting a ss prop for mine. I am going to do this based on your info. Thanks for this thread helped me out a ton. I am glad you got to that 30mph mark you were looking for.

 

[Johny25]

Re: Prop pitch selection question on a 30hp Johnson

I am glad someone got something good out of this.....lol. This little obsession to gain another 2-3mph has caused me a lot of grief.

Ok well I tried another jackplate height again today, 1.25 inches lower this time and had an even worse is with prop slip So I removed the jackplate and will not try it again.

So this is my final numbers to close the thread out. It was really windy and rough out today so I only ran the 14 SS at a light load.

with 875-900lbs it ran at 5660-5730 rpm at 29.6-30.8 mph = 14-15% slip

I am not sure how to get the slip % down other than to cup the prop, but I think this will hurt my top speed?

 

[steelespike]

Re: Prop pitch selection question on a 30hp Johnson

I checked a couple of etec Note the prop size. 25 and 30 hp tests. A 30 on a starcraft 1620,570 lb boat about 1000 total weight 12" al prop.
5800 rpm 27.6 mph 9% slip Slip. A starcraft V16 280 lbs about 900 total 12" al prop 6000 rpm 31.6 the slip is extremely low under 1% so I suspect something isn't just right. Looking at these numbers and the prop selection I wonder if your tach may be a little high.
If we take your speed ,prop size,ratio ,substitute a more typical 10% you get 5550 rpm.
From my limited experience it appears aluminum boats of similar size can have vastly different speeds
with comparable size motors.I'm sure some difference comes from the bottom configuration but I believe also the construction of the bottom many rivets,seams, keels ,placement of any spray rails etc.
can affect performance.

 

[Johny25]

Re: Prop pitch selection question on a 30hp Johnson

Well it jumps up to about 5550 rpm fairly quick (about 5 sec) and then slowly goes up another 120-150rpm (about 20 sec) and levels off between 5650-5700. It does sound like a lot of slip to me? The GPS I am using is on one of those smart phones so I am not sure if they are the most accurate? I used 3 different GPS apps and all were within 1 mph of each other. The 2 without the hundreth mph reading kept saying I was doing 31 but the GPS may have been rounding up?

Hey the good thing is I can push an 1100lb load at 28mph with the 14, that makes me really happy considering it is comparable to the new E-tec stats

 

[jasper60103]

Re: Prop pitch selection question on a 30hp Johnson

I am glad someone got something good out of this.....lol. This little obsession to gain another 2-3mph has caused me a lot of grief.

...

Hey, Johny.
Thanks for conducting these tests and sharing the info.
I'm sure it will come in handy for many others including myself.

So you made your wife get on the scale, eh?

 

[steelespike]

Re: Prop pitch selection question on a 30hp Johnson

I do think your doing really well and it just occurred to me your running a 14 footer that might struggle a little more compared to a 16 with about the same load.Which could result in slightly higher slip.
We had a 15ft aluminum utility with an old gale 25 it Struggled to plane with 4 adults.
we got a 18ft bare bones Crestliner utility same motor planed easily with 6 adults.
The larger footprint really helped.I've told this so many times some are probably sick of hearing it.lol

 

[Johny25]

Re: Prop pitch selection question on a 30hp Johnson

Hey, Johny.
Thanks for conducting these tests and sharing the info.
I'm sure it will come in handy for many others including myself.

So you made your wife get on the scale, eh?

Well I didn't get to see it personally but she told me what the scale said...... so I added 25lb to that and called it good . The light load run is with just my 6yr old and me. The heavy load runs were conducted with the wife, our 3 yr old and the 2 seats for them. Somewhere in the 225-240 lb weight increase.

Hey steelspike, I have a bow mount (28lbs), battery (50lbs), custom casting deck and storage compartment (35lbs), my 6 yr old (55lbs), and anchor (15lbs) all on or in front of the front bench seat. Thats about 185lbs that has to be up there or the boat will porpoise. And if I trim it to the last notch on my motor it will still porpoise a little even with 185lbs up there. Yeah the boat actually measures 13' 11"

I figure 30-31mph is not bad, I ran down a 16' lund with a 50hp 4 stroke yamy yesterday which made me feel good Granted he was pushing far more weight than me being it was one of those wide deep v mr. pike style lunds. But it still felt good, and my 6yr old thought it was fun.

Thanks to all who followed this and helped me out I may at some point get my prop cupped so I can run it closer to the surface but for now I am going to leave it alone and turn my attention to catching some fish next time I go out.

 

[pootnic]

Re: Prop pitch selection question on a 30hp Johnson

I remember reading torbjorn's post and I think he said that prop(14,SS)is more like a 13"pitch,so that should help the slippage issue.
I really don't know just thought I'd throw that out there.
I like reading posts on these smaller outboards/boats and I'm sure other people out there googling about their problems will find this information very helpful/interesting.
It's still funny that lowering of the jackplate made the prop "slip" worse.I bet you will still play with that jackplate at a later date,until then enjoy your boating.

 

[Johny25]

Re: Prop pitch selection question on a 30hp Johnson

The only thing I can possibly think that is causing the prop to cavitate/slip is the 3 runners on the bottom that are right in the middle only about 2 inches apart? It just makes no sense to me why it slipped worse than when I had it at 2 and 5/16" up. Actually it ran best at the 1.75 inch jackplate I originally had on there. But it was spraying water all over the place and into the back of the boat. I have tried about 7 different heights now and the only spot it won't slip or spray water all over is all the way down on the transom. I tried all trim levels at all the heights and just never could get it to plane right without slip/cav?

I still am getting 30mph so I am happy : )

 

[jasper60103]

Re: Prop pitch selection question on a 30hp Johnson

...

I still am getting 30mph so I am happy : )

I think 30 mph is way cool.
I guess I have some work to do, LOL.

 

[mauro1984]

Hy Johny25, excellente info you got, Now im in the same problem, I purchase a Tohatsu Everun 30 hp 2 stroke and came with 10" prop pitch, of course hit the 6000 rpm, so I bought on ebay a Solas Amita 4 with 14" pitch, it means is a 4 blades propeller must be much less slipage. I think thats your best option for decrease slipage.