1985 Evinrude 50 - Prop options for a noob...

DrFast555

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Nov 23, 2020
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Hello all,

I just bought my first boat, a 1989 Key West 17 CC.... It came with an older Evinrude 50hp (about 1983-1985ish he told me). The motor was off a larger pontoon boat and has an 13" 11 pitch prop. He also had a 13" 18 pitch prop.

He told me with one person on the boat and the 13 11 prop, he could only go 23ish knots.

From my reading here It looks like a 12.5 13 would have been OEM.....

Just wondering which prop I should start out with???

Thanks in Advance for the advice and I am glad I found this forum - A wealth of Info!
 

DrFast555

Cadet
Joined
Nov 23, 2020
Messages
9
Hello all,

I just bought my first boat, a 1989 Key West 17 CC.... It came with an older Evinrude 50hp (about 1983-1985ish he told me). The motor was off a larger pontoon boat and has an 13" 11 pitch prop. He also had a 13" 18 pitch prop.

He told me with one person on the boat and the 13 11 prop, he could only go 23ish knots.

From my reading here It looks like a 12.5 13 would have been OEM.....

Just wondering which prop I should start out with???

Thanks in Advance for the advice and I am glad I found this forum - A wealth of Info!
Forgot to add other info:

Normally only two of us in the boat with our 5 lb dog. We run mostly in the spring fed rivers north of Tampa for fishing and cruising. Occasionally we will head to a beach. Never plan to pull a skier or tube... I'd like to get to 30 knots if possible with only 50HP (keep me real if not possible!)
 

WesNewell

Chief Petty Officer
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Jan 3, 2018
Messages
497
Assuming the boat and engine are in good condition, with the engine mounted at the proper height for performance, you should be able to get maybe a little over 30 knots with a minimal load with the 18p prop. This assumes the GR is 2.42 for that engine and boat weight is 850#. Otherwise all bets are off.
 

Sea Rider

Supreme Mariner
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Sep 20, 2008
Messages
12,345
Max Speed is Relative, WOT rpm numbers is All. To start with need to install an induction tach on that oldie. Need to know the min-max WOT rpm range factory stated for said motor, go for a wot spin with 2 up along fishing gear and report the max wot rpm the motor achieve on a flat calm water scenario. The motor must be in top healthy runnig state...

Test both current props. and keep the one that will achieve middle to max of the wot rpm range. 11 and 18 pitch props are diametrically opposed to each other. The 11 will probably over rev the motor, the 18 will surely lug it, that's why an induction tach is a must install to take the max out of the combo...

Happy Boating
 

DrFast555

Cadet
Joined
Nov 23, 2020
Messages
9
Max Speed is Relative, WOT rpm numbers is All. To start with need to install an induction tach on that oldie. Need to know the min-max WOT rpm range factory stated for said motor, go for a wot spin with 2 up along fishing gear and report the max wot rpm the motor achieve on a flat calm water scenario. The motor must be in top healthy runnig state...

Test both current props. and keep the one that will achieve middle to max of the wot rpm range. 11 and 18 pitch props are diametrically opposed to each other. The 11 will probably over rev the motor, the 18 will surely lug it, that's why an induction tach is a must install to take the max out of the combo...

Happy Boating

Thanks for the advice! I'll add the induction tach before I go out this week. Going start out on the 11 (which looks almost new) and will report back the numbers after this weekend!
 

racerone

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Dec 28, 2013
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No not run full throttle with the 11" pitch prop.----Try / borrow a 15" pitch.
 

DrFast555

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Nov 23, 2020
Messages
9
No not run full throttle with the 11" pitch prop.----Try / borrow a 15" pitch.
Gotcha, I think I will jut buy a 15 p prop and then go give it a try.... I don't want to bog or over-rev this old motor! I found a Solas 2311-123-15 online for $80...
 

WesNewell

Chief Petty Officer
Joined
Jan 3, 2018
Messages
497
If that engine is in fact a 2.42GR the 18p prop should be the right one, or very close to it.
 

Sea Rider

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Sep 20, 2008
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12,345
Thanks for the advice! I'll add the induction tach before I go out this week. Going start out on the 11 (which looks almost new) and will report back the numbers after this weekend!
Yep, way to go. Report your wot rpm numbers with the 11 pitch to go from there...

Happy Boating
 

DrFast555

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Nov 23, 2020
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Hello all, Finally got to get out and test it out...

15p WOT was 54-5700 rpm with 600 lbs of people and gear... depending on the trim adjustment - 29mph max by the gps on my phone

18p -WOT was 3800 rpm (definately bogged the engine) top speed was 25ish

11p WOT was too high 9went up to 6000 at one point so I backed it off. 23mph top speed....

Looks like the 15p was the winner!

Too bad I destroyed that prop on the way back in... Hit a submerged rock on the Chassahowitzka by making a wrong turn... ordered a new one again $80...
 

DrFast555

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Nov 23, 2020
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I'm not sure how to know the final Gear ratio on this old guy.... The model info sticker has long been gone... and who knows what has been done to the insides of a 1983-ish motor...
 

racerone

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Dec 28, 2013
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Winner.-----Put in gear.-----Turn flywheel 10 turns.----Count turns of propeller.----Calculate gear ratio.----Should be .414------12 teeth on pinion and 29 on forward gear.
 

Sea Rider

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Interesting prop data and thanks for posting, very few does so. What's the min-max wot rpm range factory stated for said motor ? Is it 5000-6000 wot rpm ? Test combo again on flat calm water cond with a new 15 pitch prop, distribute deck load evenly and set trim to neutral once combo is on plane and leave it there while maintaining full plane.

How many souls were on board when the 15 prop achieved those stated wot rpm numbers, plan boating with such number frequently or varying the souls on board occasionally?

Knowing the current gear ratio it's of no importance, for recreational boating need to prop the motor right with current gear ratio to run at least middle to max of its wot rpm range as loaded.

Happy Boating
 

DrFast555

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Nov 23, 2020
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I'm not sure about the factory numbers for the motor... it's an 1983ish 50hp Evinrude. I'm not even sure the exact year because the sticker is gone...

15p numbers had 600lbs (three people summed up to 550lbs) and 50 lbs of food and beverages). Normally it would only be two of us total weight of 400lbs....

I will use the 11p prop for the springs like Weeki as it will make me move slower at idle. And maybe the 11p when I load up the boat with visitors....
 

Sea Rider

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Sep 20, 2008
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The wot rpm range for said 50 HP is 4500-5500. So a 15 pitch at 5400-5700 wot rpm is right for that application and current stated load, throttle less if plan boating with just 2 souls on board.

Just for the record : Test combo again on flat calm water cond with new 15 prop, distribute deck load evenly, once combo it's on plane set trim to neutral. Report the wot rpm achieved under such trim setting with 600 lbs of passengers/gear as previously tested.

Changing the prop for constant different boating applications will bore you real fast....

Happy Boating​
 

WesNewell

Chief Petty Officer
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Jan 3, 2018
Messages
497
Before you even start testing props, you need to make sure the engine is mounted at the proper height. Mounted too low and you need less pitch to compensate for the extra drag. Right now you are over reving a little with a 600# load. You will only over rev more with a 400# load. So first check that the engine is mounted at the proper height. Then, and only then, you can dial in the proper pitch you need for a certain load. With the engine trimmed to be in line with the hull bottom, the av plate should be no lower than the bottom of the hull. When running wot, it should be just above the water line.
 

DrFast555

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Nov 23, 2020
Messages
9
Before you even start testing props, you need to make sure the engine is mounted at the proper height. Mounted too low and you need less pitch to compensate for the extra drag. Right now you are over reving a little with a 600# load. You will only over rev more with a 400# load. So first check that the engine is mounted at the proper height. Then, and only then, you can dial in the proper pitch you need for a certain load. With the engine trimmed to be in line with the hull bottom, the av plate should be no lower than the bottom of the hull. When running wot, it should be just above the water line.
Thanks for the comment... I'll add a picture of the setup.
 
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