What size of prop do I need

[mrcombel1963]

Well I got a Johnson 140 with electric start, tilt, and trim, and the boat is 18'6" Deep V Sylvan aluminun ski and fish style.from the bottom of the stern to prop center is aprox 7" inches. presently the tach say's five grand but hey if it would do more I'd go for it. it use to move faster when we were on a heavyer longer boat but since we moved the engine to a lighter shorter boat it only gives us five. think that she max's at fifty five anyway and that is where its was when we had her on the longer boat. anyway, the tripple bladded prop thats on it now is kinda chued up and looks like it has seen better days, I personally would rather buy a new one over trying to add something to whats already missing if you get my drift, "fixing this one" maybe better to just replace and start over "yup" ! anyway that all I can tell you for now other that the engine in question is an 1982 Johnson 140 HP Electric tilt, trim, and start. she runs great since we've done alot to acheive that. only now we want to finish what we started and give it something new to move us with. it aint got to be the most exspensive stainless prop out there, just the cheaper imatation will do, of course one with the right attitude of course.
Any info greatly appreciated !

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When all else fails post your message on iboats forum.com and you'll get your quik answer.

Stacks

 

[mrcombel1963]

Re: What size of prop do I need

double post.

 

[walleyehed]

Re: What size of prop do I need

5000RPM is 800 short of where that engine will run best.
We need to know what the original pitch size was before the prop was damaged and we can go from there.

 

[mrcombel1963]

Re: What size of prop do I need

Thanks there "Kenny", but had I known the prior pitch info. I probably wouldn't' have made a post for a stupid question like what size of prop do I need, I would have used my own prior info to my advantage. I guess I'll have to use my own judgment and try to size it for myself. I'll just give it to my reputable prop repair shop, since if they can get it right the first time, they must be "Genius's".
Thanks Anyway,

-------
When all else fails, post your message on iboats forum.com and you'll get your quik answer.

Stacks

 

[walleyehed]

Re: What size of prop do I need

No 1 prop is the same on any boat...even the same pitch between 2 different manufacturers can act alot different.
If you can't tell your prop-shop the RPM, they can't set you up either...most may know thepitch of the prop but that doesn't tell them if you're at the propper RPM...very critical. If they repair, or sell you a prop in the same pitch, they're still shoting in the dark...most common mistake made.
p.s. I've not seen a prop yet that didn't have the size on either the hub under the nut or between 2 blades.

 

[mrcombel1963]

Re: What size of prop do I need

So I mentioned my max wot is at fifty five hundred, it may not be doin fifty eight or even six but its turning more than five. I really don't want to do more than fifty five because its an older engine that I depend on to get me to my favorite spots without any failures. how do I give an acurate reading so's I can get the right prop to do the job at say fifty three hundred and no more. cut and dried, give it to me !

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When all else fails, post your message on iboats forum.com and you'll get your quik answer.

Stacks

 

[walleyehed]

Re: What size of prop do I need

Point-blank...5300 WOT is lugging that engine and it will cause premature failure. If you want to "depend" on it, you better turn it 5500+. It has to do with the design era of the engine and fuel quality of that era....we don't have near the quality of fuel we once had, and raising octane is not the answer, infact it makes it worse.
You said it turned 5500 on "the other boat"...
There is no simple answer as I said, and we don't even know if the tach is accurate.
What I'm saying is there is NO 1 single prop for an unknown application.
On a 1978 Glastron SSV-176 we had a Johnson 140 on, we ran a 13-3/8X17P SST at 5600RPM.
We are at 3600ft above sea-level...a 12% drop in HP average, but we jetted and adjusted timing for this altitude, so taking into account you have rivot heads, a foot longer boat and "assuming" you're near sea-level, I'd guess at a 17P .....shot in the dark at best....
If anyone can make an educated guess at this, please do......

 

[mrcombel1963]

Re: What size of prop do I need

"Premature Failure" So your saying that running an engine on its last leg and doing maximum WOT is right for the engine, also saying that by not backing off and taking it easy is better for an engine. I asked a question of prop size as to the wide open throttle my limit is set at 5300 and your oppionon is to run it harder. I had it in the shop yesterday we ran a couple of different props and decided on the the one that'll do the job. it allowed the boat to plain out much better than it had done before without to much wash,
Pitch: 21”
Diameter: 13-1/2”
Blades: 4
Rotation: Standard
Material: Aluminum
This design was with-out delight the best choice based upon our boats designs and abilities on the water. a prop loaner program is by far the best choice a person can have since it allows the buyer to purchase the right choice based upon the buyers limits and price of their prop shop catagories, our thoughts are at ease now that our boat cruises the way we wanted it to.

-------
When all else fails, post your message on iboats forum.com and you'll get your quik answer.

Stacks

 

[walleyehed]

Re: What size of prop do I need

"I asked a question of prop size as to the wide open throttle my limit is set at 5300 and your oppionon is to run it harder."

"Your limit" means nothing as to how long this engine will last, and I did not tell you to Run WOT all the time, but it must be propped to turn the correct RPM, or you WILL stress the engine more...Running it "harder" is to run at 5300 insted of 5600-5800.
I'm sorry you don't understand the physics of a 2-stroke.
It will cost you in the end...I tried to help.


21P 4-blade is about the same as a 22P 3-blade...
I can't even turn that on my 18ft alum with a souped-up 200 at the right RPM.....You are WAY over-propped.
When it shells from running high manifold pressure (even at cruise because you don't have it propped right), the Wiseco piston P/N is 3173P I believe....
You'll be needing some before long.
I can't stop there...you see, if an outboard is not propped for the proper WOT RPM, it's lugging at cruise as well because it's pulling it so hard to keep that cruise.
The work the engine does at cruise would be much less if you had it propped for Max RPM first...you have no transmission, you have 1 gear (pitch of prop), and it would be no different than pulling your boat with a vehicle in a 40MPH zone in over-drive.
This is a 2-stroke, and is nothing but an airpump, and if you can't understand there is less stress at the correct WOT RPM for set-up, then nobody here can help ya, and if the dealer that sold you the prop didn't ask any questions about RPM, he's a poor dealer, and wants nothing but your money.