Need to replace prop on 81 Evinrude 25 hp

[osageinmt]

Just got this motor and the prop is pretty beat up, it is a 9.2 x 12.
My question is that seem like a lot of prop for a 25hp on a 14 alum with a hull weight of 206 according to the MirroCraft catalog. Don't really ever troll and if I did I'd use my elect motor, mainly just need just run from place to place looking for fish.
At least 2 adults in the boat sometimes 3, 180 Lbs to prop 220 lbs probobly each, 2 deep cycle batteries, bow mount trolling motor, tackle, coolers etc:

I'm thinking 11 pitch might be better ? am I wrong ? this is what I was thinking of getting : [h=1]Solas 9-1/4 x 11 3 blade RH Amita Aluminum Propeller[/h]

 

[steelespike]

It does seem that an 11" prop would do better with that load.
You may have to watch the rpm with no load.
You would be surprised at how well that motor would do with the same load in a bare bones 18' utility.
You should get an induction tach like the Tiny Tach.
tell them what you're using it on.Do a lightly loaded test run. Get us the wot rpm and gps speed.
For performance and motor health its important that the motor can operate within its wot rated rpm.4500-5500.

 

[Sea Rider]

Before buying blindly or guessing another prop option, test current prop if not bent and still near fully operative, Install an induction Tiny Tach or Hardline tach with programmable firing sequence, go for a wot spin you alone with lightly loaded and well trimmed boat on flat calm no wind waters. Check achieved wot rpm, then can go from there maximizing prop to run inside safe wot rpm range for that engine. Dialing a prop that revs middle to max wot rpm would be excellent for your given load.

Happy Boating

 

[osageinmt]

I have a Hardline tach/hour meter on it now, and hope to get it on the water Friday. I ordered the manual for it as well as a gasket for the cly head water cover, but won't get them till Fri/Mon.

I'm not real good at waiting, so I went ahead and pulled the lower unit off to inspect the impeller that the PO said he had replaced last fall, it seemed pliable but 3 of the vanes were turned the wrong way, put it back together right and have new one on the way.

Kinda jacked to get it out, the old prop is pretty worn and has some nicks, but I don't think it is bent should do to get some baseline numbers.

thanks for you input.

 

[Sea Rider]

Will love boating with a tach, where do you plan to install it, on throttle arm, center console ? Impellers runs CW, rotate drive shaft CW while seating linear on top new impeller, wet it before seating liner to slide faster, It's a must tach original factory delivered prop, if it's a good performer can replace same if you break or gets spun as you already know previous achieved wot rpm. If you preffer can go from there maximizing prop in order to get best top performance out of your combo specially if running portable engines.

Happy Boating

 

[osageinmt]

No Title

Got out on a lake today, it was beautiful weather, not too hot with just a very light breeze. Caught a bucketful of perch.

However with just me in the boat, 1 deep cycle battery, 6 gal gas, tackel, cooler, etc: about a light a load as I will ever have.....I could only turn 4420 RPM. I forgot to turn on my GPS duh.
The data plate on this motor tells me 4500 to 5500 RPM operating range, peak horsepower at 5000 RPM. So I'm down a bit. Motor sounds like it's running OK dosen't sputter or cut out, just dosen't rev like it should.

Now the prop on the boat is beat up/ very well worn.

I should also note that the motor may need to be raised up, seems too low on the transom to me, but I didn't even think to adjuat the tiller pin or whatever that is called on the motor clamp. Anti cavitation plate is right at 1 1/2 inch below the bottom of the hull. pic below

Is there anything I can do to make sure the motor can actually turn 5000 RPM ? I mean to make sure that the motor is running right . compression check was good 115 psi in both cly, no leaks anywhere that I can see water or fuel.. should put in new plugs I guess, old ones look just fine tho.

? ? ?

 

[osageinmt]

No Title

Opps that didn't work like I ment it to.

this is where the motor rides on the transom. I think it's too high, anyone have an opinion on that ? too high ? too low ? I don't know.

any insight will be greatly appreciated

 

[Sea Rider]

Best engine height should be dialed under trial and error. Ideal for a portable engine to get the max HP out is for water flow at speed to pass slight under small upper water deflector plate, that's well trimmed and weight balanced boat on flat calm no wind water cond. With you alone, are you experiencing over or back transom water splashes when on plane. If not, there you are at the sweet engine/transom height.

Will need to drop at least one pitch to pull your revs up, by how much, don't know as you could achieve 200-400-600 + RPM. This is not a exact science must test with a wot outing as if you were stealing the combo.

Happy Boating

 

[osageinmt]

Thank you.

Yes I got quite a bit of water kicked up over the transom when I would open it up. Sadly I did not think to look over the transom to see where the water was passing over the leg.

 

[Sea Rider]

If the splash is over the transom, need to raise engine up by means of wooden shims with same transon width untill the splash is over. I'm glad about your disposal to look over transom to see where is the splash being produced. None who has asked for help with same issue want to look over losing precious boating time testing blindy engine heights over and over again when at most with 2 shim tests will be at the sweet engine/transom height.

Before shimming must meet these boat cond :





Shim up your engine to achieve this : Look over transom once on plane while shimming with different shim heights untill this cond is met. That's the sweet transom height for any engine, specially portable ones in which you need to get all those horses out of the barn at once. From there can go for a prop maximization if in need to optimize your boating requirements. Post results..



Happy Boating

 

[osageinmt]

Thanks, the pic of the motor in the water is what my 15 hp short shaft Evinrude looked like with 3/4 inch shim under it.

I just put the same 3/4 inch shim under the 25 short shaft Evinrude on the boat, hope to get on the water monday .


The beat up prop, would that contribute to the motor not getting up to proper RPM ?

 

[steelespike]

Before prop selection we need to know the gps speed as well as the wot rpm.
You prop diameter may actually be less than indicated from years of wear and tear.
It would be pretty simple to check that you're throttle opens all the way.
While timing is pretty simple it wouldn't hurt to check the advancement.
The rpm and the slip are the tough numbers to get.
The gps speed along with the other hard numbers ratio,pitch (rpm) the calculator will determine slip
if slip seems unreasonably high or low we need to try to determine why.

 

[osageinmt]

Got on the water today for a little while, pretty choppy but I did make 1 run. Had about a normal load gas,batt, gear, wife and a gradkid.

Top speed I got was 21 mpg by my Garmin GPS......max RPM was 4503 according to the Hardline tach/hourmeter. The tag on the motor lists operating range as 4500-5500 rpm peak HP at 5000 rpm

to me just barely getting into the operating rang of the motor with the load I had mean I need to drop to a 11 pitch prop, that's what was shipped with the motor and I guess the Evinrude folks have a pretty good idea what will work in a wide rane of boats and uses.

​ The motor seems to be trimed about right looking over the transom to see the water going around the leg, could not get a pic, I just knew I was going to drop my cell in the lake. looks about like the pic that Sea Rider posted above, thanks for that by the way. The shaft of the motor is pretty close to 90 degrees to the transom.

So given all that I have ordered a Solas 11 pitch for the motor, I will post results here by next weekend, hoping for a calm day soon.

thanks to you all for help and direction.

 

[osageinmt]

No Title

 

[Sea Rider]

If you will be boating often with stated number of passengers and gear included a 11 pitch hopefully will pull revs to medium wot range (5000 rpm) will have better hole shot moving along current weight with less engine effort than before.

The issue is that won't know in theory how many rpm the 11 prop is capable of rising, as the near rule of thumb that states 150-200 + rpm for every 1 pitch in reduction probably does not apply to medium light configurations as we're beginning to see specially on light ones.

​Happy Boating

 

[steelespike]

But for the 4500 the numbers seem pretty good. I wonder what the all up weight is?
Seems like the 25 might be a little faster. On a light reasonably fast boat speed should be about 30.
I would say it will feel more powerful with an 11" pitch. Might make a little more speed because you will be in the power range of the 25.

 

[osageinmt]

With any luck I can get 4800 - 5000 RPM, if not I can sell the 11 pitch prop on CL, and order a 10 pitch..... lots of 25 hp jonhson/evinrudes around here.

thanks for all your help. will post results with the 11 pitch next wwek.

 

[osageinmt]

Well I guess I will be waiting some more...got the prop I ordered today, and it is the wrong prop for my motor.

I left the S of the end of the part number so instead of a prop for 13 spline non thru hub exh I got reg thru hub exh. it will fit my 15 hp Evinrude, but 11 is too much prop for any boat I will use the 15 hp on.

Oh well, Michigan Wheel prop on the way thu iboats.com parts

 

[osageinmt]

Got the correct prop at last, and make it to the lake yesterday.
Average load in the boat and I could run 24 mph by GPS, at 4920 RPM to 5040 RPM depending on the chop....winds were very light to none. Pretty happy with the result. This is a 9.25X11 3 blade prop.

I had run last time with a 3/4 inch shim under the motor to raise it up, this trip I added a 1/4 inch shim to it to give a full inch, seemed OK except I guess the prop would cavitate at times, you could feel the boat slow down, and you would see the RPMs go up on the tach, hit 5500, 5600, and a scary 5720 RPM once. It would do this for no apparent reason, I wasn't crossing a wake, or in rough water...just scooting along at 4900-5000 RPM and it would just lose momentum, and rev way up.

I'm thinking I have the motor too high now, tho it looked OK when under way, the way the water was comming of the leg of the motor. So I have removed the shims, and went with just 1/2 inch on the transom, this puts the anti cavitation right at 1 inch below the bottom of the hull. I will give that a try in a few days.

I have ordered a 9X10 3 blade prop, I hope this will put me running at around 5300 to 5500 RPMs.

thanks for all the tips and pointers

 

[steelespike]

24, a nice increase. When making changes you should do one at a time and test.
Probably not much difference but we don't know how it does with a 3/4" stick.
​ Pretty obvious 1" was too much.
Sea Rider was 100% right about your setup. but there are rare exceptions.
We had a beautiful run about kit boat with a 18 on it it was all done up with full front deck ,split center deck and a rear deck on either side of tne motor
A big wide boat and our great dane rode on the front deck. With all that deck up front it was just a little bow heavy and we ran the 18 in the 4th notch.
I rode on the stern deck next to the motor with the gas tank on the back seat. On a good day it would do 23-25 mph.18 was rated for 27 on a light reasonably fast boat. It never porpoised or ventilated except in a severe turn when the boat would slide.
Point is you might try working on the trim. Sometimes you can buy or make a wedge that will allow you to adjust for half a notch.
Depending on how your use it you can add or subtract 1/2 a notch.
Every boat I've had with manual trim one notch would not be quite enough but the next notch was just a little too much.