Author Topic: Another prop question??????  (Read 1573 times)

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Offline Longknife 76

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Another prop question??????
« on: May 02, 2008, 08:05:19 AM »
I have a 50 horse evinrude #E50TSLECC. I need a prop, in the book said I need a 12 1/4 X 15 prop. I haver found about every size under the sun EXCEPT a 12 1/4 X 15. (Ebay) I know some different sizes/pitches will work but what adv. or disadv. are there in changinng sizes/pitches, I just want to go fish'n!!!!!!!!!!!!!! Thanks, Ed

Offline GRIMJIM

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Re: Another prop question??????
« Reply #1 on: May 02, 2008, 12:21:33 PM »
I don't think I would change the pitch. Your engine turns at a very high rpm and "speed props" put a lot more stress on the motor than they were originally designed to handle. I have a 150 hp mercury and it turns 5,000 rpm if I remember correctly so any pitch deviation would have a great impact on the motor. Not enough pitch and the engine over revs, too much pitch and more stress. I'm no expert though, hopefully someone with more experience than me can help you out here.
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Offline Sweetwater

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Re: Another prop question??????
« Reply #2 on: May 02, 2008, 08:47:05 PM »
This may not be your best answer, but you do have several choices. Again, these are choices. You have a 50hp Evinrude - is it on a fast boat or a slower boat? Simply to fish, the short answer is you can put on any prop that will fit your lower unit. You don't say what your choices are in availability or if they are 3-blade, 4-blade or whatever. Switching from a 3-blade to a 4-blade will equal an inch of pitch change. Do you use a tachometer? If you do, good, that way you can keep the rpm's out of the red zone. You can keep it that simple. Or, you can complicate it. One inch change in pitch is about equal to three inches change in diameter, and maintain approx the same rpm range. (I'm trying to remember some formulas from 40 years ago when I was dabbling in Naval Architecture and Marine Engineering.) On our inboards we basically used the largest diameter that we had room for, and enough pitch to control the rpms - and we didn't run full throttle - ever. We also didn't listen to the 'experts' at the marina. We did what we needed to do to make the boats do what we wanted them to do - simple. On my outboard, it was supposed to have a 3-blade - I switched to a 4-blade and got better power to get the boat going under load and just as much speed when light and never did exceed the rated rpms. Most of my outboards were slower boats, like the mid-'50's Crestliners. They were rated for 70hp. I ran an 18hp Johnson for over 20years on my 15ft, sometimes with a 10hp or 7 1/2hp beside it in a pseudo twin arrangement. The engines were small enough to not create a synchronizing problem. Never did get it over 20knots. With a 40hp Evinrude, I did get it to 25knots, but it had an electric shift and I didn't like that for trolling. Forever a dead battery. I later traded for a newer generation 25hp Johnson - which I loved, and it would do 22knots. In all of this, this boat spent most of its life on the ocean and on big lakes and rarely got over 15knots with the loads of people and camping gear that we carried. The 4-blades that we weren't supposed to use were far better for our application than the stock 3-blades.

In your application, with the fishing as first use, I would get the closest to your present diameter (larger diameters get further away from the turbulence caused by the skeg on the lower unit, thus getting a better bite) that was available, but not larger than the 'factory issued' prop. Did your engine reach its rated rpms with the aforementioned prop size? If it turned too fast, than you could use more pitch. Conversely, if it turned too slow, you could use less pitch. This is all less rocket science than if you were running a high performance rig for water-skiing or racing, etc. About all I can offer  - but should be enough to get you up and running.

Regards,
Sweetwater
Regards,
Sweetwater

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Offline deltecs

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Re: Another prop question??????
« Reply #3 on: May 02, 2008, 09:48:19 PM »
I have a 50 horse evinrude #E50TSLECC. I need a prop, in the book said I need a 12 1/4 X 15 prop. I haver found about every size under the sun EXCEPT a 12 1/4 X 15. (Ebay) I know some different sizes/pitches will work but what adv. or disadv. are there in changinng sizes/pitches, I just want to go fish'n!!!!!!!!!!!!!! Thanks, Ed

I happen to own a couple of 50 OMC outboards used in my Commercial fishing operations.  I am not at home, currently taking care of business elsewhere.  If you will IM me for a reminder, I'll look at my props at home upon my return and let you know what I've used successfully.  At first impression, I think that is the pitch and diameter of the props I'm using now, but cannot verify this until I get back home.  I'd be glad to help you.
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Offline Longknife 76

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Re: Another prop question??????
« Reply #4 on: May 03, 2008, 05:20:09 AM »
Thanks for the replies,. I have currently a 12 1/4 X 15 prop,  50 hp omc. mounted on a 18 foot Lowe "roughneck bass boat. It has a 20 gal tank, 3 batteries two anchors, swivel seats mid mount console, built in live wells, storage boxes and two swivel seats. I don't know the exact weight but the plate says 4 persons at 550 lbs or 1100 lbs total weight. It does have a tach. The prop I found is a 12 1/2 inch 13 pitch prop. Would you put this size on this rig???/Thanks, Ed

P.S. I use this boat for fishing on smaller lakes in S. Illinois

Offline Sweetwater

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Re: Another prop question??????
« Reply #5 on: May 03, 2008, 09:54:08 AM »
I just looked at the Evinrude website and although it does not (at least I didn't find it) give specific sizes, it does say a variety of sizes are available as one size does not fit all applications. It also stated one inch change in pitch would change engine rpms by 250rpms. So, if one inch of pitch approximates three inches of diameter, then an increase of 1/4 inch in diameter should drop rpm by 250rpm divided by 3 inches times .25 inches=20.8rpm which is insignificant for your change in diameter - provided you have room to swing that extra .25 inch of diameter. Dropping 2 inches of pitch yields 250rpms times 2 inches=500rpm increase. Your tach should keep you out of the red zone if you decide to go this route - nothing dictates that you run full throttle except you. If your motor will clear a 12 1/2 inch diameter, this will work as you control everything else. Happy Fishing!

Regards,
Sweetwater

Regards,
Sweetwater

Courage is being scared to death but saddling up anyway - John Wayne

The proof is in the freezer - Sweetwater

Offline Sweetwater

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Re: Another prop question??????
« Reply #6 on: May 03, 2008, 11:03:27 AM »
Some more to chew on-

One question - you stated "the book said you need a 12 1/4x15 prop". What book? Prop size is usually dictated by load and application. Lots of variables there.

On the Evinrude website, I found some performance guides. From that, I have extracted the following:

The present generation of 50hp Evinrude will swing up to a 14" diameter propeller.
 
So, making a few assumptions, knowing full well how shaky that can be, here goes:
IF your present setup runs around 26knots at around 5000rpms, THEN changing to the 12 1/2x13 prop should deliver about 23 knots at around 5500rpms.

IF your present setup runs around 30knots at around 5500rpms, THEN changing to the 12 1/2x13 prop should deliver about 26 knots at around 6000rpms.

This is all in keeping with the Mfg's given rpm operating range. The drift being, whatever "speed" you are getting now will decrease (probably) by about 13% at an increase of about 500rpm by changing to the 12 1/2x13 prop. Not Earth-shattering. On the up side, if your boat is laboring with its present prop, it might just run easier with the 13" pitch.  Watch your tach and Go Fish!

Regards,
Sweetwater

Regards,
Sweetwater

Courage is being scared to death but saddling up anyway - John Wayne

The proof is in the freezer - Sweetwater

Offline Savage

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Re: Another prop question??????
« Reply #7 on: May 04, 2008, 02:49:32 AM »
Long Knife,
If you bought your rig new as a "Package",  it was likely propped with the mid pitch prop, designed to give decent performance with "Average" loads under "Average" conditions. If you fish with a hefty fishing partner and carry a lot of tackle, you might be happier with a 13" pitch. If you fish by yourself and don't load your boat down much, you might be happier with a 17" pitch.  Ebay, would probably be the last place I'd look for a prop. Sometimes your local dealer has a good selection of used and rebuilt props at reasonable prices. Plus, he can help you prop out your boat to fit your applications. Frequently, they will let you try a couple of different props to see which one you like the best before you buy. I would seriously consider going to a SS prop. They perform better than the aluminum, and are much more durable. Of course you'll need a spare--------------for that time you hit the rock wing wall 10 miles from the ramp!!!!
Savage
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Offline Sweetwater

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Re: Another prop question??????
« Reply #8 on: May 04, 2008, 10:11:35 AM »
You know, Savage makes a good point about carrying a spare prop. Also, spare shear pins.
Back in my teens, a pal and I were in his 18ft Foley boat on Passamaquaddy Bay in Maine when we hit a log floating just below the surface. The prop was OK but busted the shear pin. No spares, so we searched the bottom of the boat and found, praise the Lord, some nails the boat builder had dropped during construction. They were galvanized and soft, but small enough to fit the pin hole. We limped into St Andrews, New Brunswick, Canada, and (Sunday afternoon) to got the local outboard dealer to open his shop (his apartment was upstairs over the shop). He was a Mercury dealer and we had an Evinrude, but he gave us a couple that one of them should work, charged us 50 cents American and sent us on our way. Having a spare would have saved us several hours on getting home.
Back to the prop, nothing says they both have to be the same, so if the bargain you get isn't the 'right' one, it will lead you to the correct size and probably make a good spare. Again, 'you' ultimately control the engine speed, so watch the tach and let it help you stay out of trouble.

Regards,
Sweetwater

Regards,
Sweetwater

Courage is being scared to death but saddling up anyway - John Wayne

The proof is in the freezer - Sweetwater

Offline Savage

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Re: Another prop question??????
« Reply #9 on: May 04, 2008, 03:55:24 PM »
Should expand on the spare prop thing. You should also have a spare prop nut, thrust washer, and cotter key. And for goodness sake, be sure and bring the TOOLS to change the thing!! Takes a long time to cover 5 miles with the trolling motor! Or so I've heard--------- ::)
Savage
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Offline Longknife 76

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Re: Another prop question??????
« Reply #10 on: May 06, 2008, 03:19:37 AM »
Thanks for all the tips, by the way "the book" is the one I got with this rig but I got it used so I don't know if the prop has been replaced or not. "the book" said 12 1/4 X 15 but the local dealer said it could take a 12 1/2 x 13 and be "OK". Just don't want to get the wrong thing.........Thanks, Ed