Evinrude 15 Prop

[chevysam41]

Hello All,

I have a 1976 SS Evinrude 15 and need to get another prop because one of the fins on the original part is cracked. I see replacement props range from ~$70-~$150, depending on brand, pitch, material, etc. If I am replacing the prop anyways, is it worth it to get a stainless prop or should I stick with an aluminum?

Since I am replacing the prop anyways, this may be a good time to talk about the performance of this outboard. This motor is mounted on a 1973 Sears aluminum 13.5' Vhull. I don't know how much the boat itself weighs, but at the bow, I have a screw on trolling motor (~10lbs) and battery (~65lbs?). At the stern, there is the outboard (~90lbs), 6 gallon poly gas tank (~38 lbs full) and myself (~220 lbs) and there is probably 15 lbs or so of fishing gear and misc equipment spread out throughout the boat. Under this setup, I get 18 mph (smooth water, no wind) on a GPS app I downloaded to my phone. When my 115 lb wife sits up front, that drops to 14 mph. Does this speed sound right? From what I'm reading that sounds a bit slow, but I know the weight up in the bow probably isn't helping matters. I've tried various trim angles and no change in angle seems to make a difference.

I can provide background info on the motor itself if needed, but it runs great, just slow. I had just gotten a tachometer for the motor and had intended to see what RPMs were at WOT before I realized the prop was in bad shape. Maybe it needs a different diameter or pitch? Current is 9.5x10".

Thanks for the help!
Sam

 

[racerone]

I think step # 1 would be to run it with a factory TEST prop.--------That will determine condition of the motor.-------Once you know that you can determine what to do.------An 8" pitch prop might work better for a heavy load.

 

[chevysam41]

It took me some time, but I tracked down a replacement prop (9.5x10") and took it out on the water yesterday evening. At WOT, the motor would spin to between 5300-5400 RPMs and then over the next quarter mile or so would climb to around 56-5700 RPMs. The highest it ever got to was 5800 RPMs. I'll add by saying that prop is fairly dull, not sure if that makes much of a difference on these motors.

The factory manual for this motor indicates that the full throttle operating range is 5500-6500 RPMs, so I am coming in on the low end of that spectrum. What do you guys think? Should I get a replacement prop in the same pitch (one I tested with is borrowed) or look at something different? Aluminum or SS?

Thanks in advance for the help!
Sam

 

[F_R]

It needs to get up to 6000 to make 15 horsepower. You are close, but not quite. Maybe close enough.

 

[raczekp1]

i would choose prop with 9.25 x 11

 

[jimmbo]

i would choose prop with 9.25 x 11

If a 10 is too much pitch, explain how an 11 would be better

 

[oldboat1]

I used a Solas 5 pitch four blade prop last year on my 9.9 kicker motor. Idea was to slow troll without having to idle down quite so far, and that worked out well.

Going to a four bladed prop might give you added control carrying the weight, and dropping pitch would maintain or increase rpms (drop at least an inch over the three blade to maintain, so a 7 or 8 pitch in the four blade might get it.) When I was looking, 5 and 7 pitches were readily available in the 10 inch diameter (don't think there was a 9.25 or 9.5 diameter, but could be wrong). A 10X7 might be perfect.

In the meantime, might try steering from the middle seat and see if that makes a difference -- if that works out, get a tiller extension.

I like aluminum props as I would rather replace a bent up prop than a lower unit. If you have a shop in the area (old-time type with some well used stuff), you might be able to test out a couple on the cheap -- or at least replace your current prop with one in better shape.

 

[ondarvr]

As stated, going to an 11" would be going the wrong direction. The 4 blade 7" and 8" props are normally the high thrust type, not really designed for planing or speed, and may raise the RPMs too high, but if they're a normal type they may work.

 

[oldboat1]

^^Point is good.