1978, Evinrude 115 replacement prop?

[Mr.Stuart]

I took the Starcraft out this weekend and ran over a log, it bent up the prop a little, not real bad, but it's a little chipped and dented, the prop that's on the boat now is a 13x19 3 blade and the boat seems to do ok with it, top RPM is about 5,000, and top speed is somewhere around 40 to 45 MPH.

I just replaced the throttle cable, and before I replaced it, I was getting close to 50 MPH at almost 5,500 RPM's so my RPM's have dropped a little but I'm thinking that is due to the new throttle cable, and with the high end around 5,000, I feel that's adequate at least for me, and the prop that's on it seemed to me to be a little worn, and I had considered replacing it anyway, but I'm not sure with what.

The boat is used for cruising, not really much water skiing or anything, just going out and putting around, doing some fishing and such.

So the question is, what prop do I want to run on it, 3 blades? 4 blades? I was doing some looking on eBay, and can't seem to find a 13x19 prop, so where do I go from here? what size and pitch do I want?

Stuart

 

[steelespike]

Re: 1978, Evinrude 115 replacement prop?

My first thought is 50 my be a little optimistic.I think gps speed would be about 42 unless you have an excellent setup.I would get the throttle cable working right so you can be sure your getting wot.Otherwise it will be difficult
to evaluate which prop you need and can't tell the results of new prop.Important to know your at wot and max rpm and speed.

 

[walleyehed]

Re: 1978, Evinrude 115 replacement prop?

5500 is the lowest RPM you'd ever want it propped for.
This crossflow likes 5800 with a normal load.
I agree on the above post as to the throttle cable not being set up properly.
I've calculated the speeds at the given rpm and I'd guess you have a dash-type speedo with a pitot tube on the rear, or your tach is off.
50 would be hard to reach with that rig....I have an SS 18 with a modified 200 'Rude...yes, a 200, and 50 is moving on across the lake with the 200. In fact, at about 52 it's getting almost so loose it's 2 hands on the wheel and chinewalk is "right there". This hull doesn't like 50 without mods.
By calculating what you give, I see 40 around 5000 and "maybe" 43-44 at 5500.
That boat/engine combo does best with something like a 17P Stiletto...if properly set-up, it does good with an 18P Raker or a 17P Turbo.
The best results will also be obtained if you mount the engine in the third set of holes down when mounted direct to transom.
Get your throttle cable trunion nut set up correctly and barrow a GPS AND a prop if needed...get us some numbers (GPS with a KNOWN prop) and we can get ya real close. 5500 was great on 1978 fuel....you need 5800-5900 on todays fantastic crap fuel to keep the coking and carbon build-up down so this engine does not self destruct on ya....

 

[Mr.Stuart]

Re: 1978, Evinrude 115 replacement prop?

I have a GPS, but wasn't paying attention to the speed readings I was getting off it the last time I was out, and yes, it has a pitot tube on the back, maybe I lost the rpm's because of the log strike, I didn't notice the damage to the prop until after I was out of the water, maybe that could cause the RPM loss?

When I replaced the cable, I thought I had everything dialed in because all settings are the same as before it broke, the idle is down to around 1,100 which is about as low as I can take it, I didn't change anything in the remote or at the engine, only removed the old broken cable and replaced it with a new one, the engine runs great, no hesitation, it runs out and idles great.

The engine offset is mounted in the second set of holes from the transom, that's where it's always run it's entire life, that's where the guy ran it that I got it from and he's had it since new and told me to leave it there, and it looks to me to be exactly 90 degrees to the back of the boat at that setting.

I plan on going out again next weekend, so I’ll get some better readings, I can fix the prop that’s on it, it just looks wore out to me, but I can get the dents out of it enough to run it for a few minutes. It actually looks more wore out then dented to me, I should have taken pictures and posted them.

Stuart

 

[walleyehed]

Re: 1978, Evinrude 115 replacement prop?

"second set of holes FROM the transom"......
I think you are referring to the tilt pin. I'm talking about the engine mounting bolts. It's very easy to raise the engine with the help of a buddy. Are you dead-set on staying with aluminum?
I went to SS years ago after folding up enough blades in the trees to fill the back of my pickup with.
Don't let the Myth of "SS props will destroy your lower unit" get you...it's simply not the case.

 

[Mr.Stuart]

Re: 1978, Evinrude 115 replacement prop?

"second set of holes FROM the transom"......
I think you are referring to the tilt pin. I'm talking about the engine mounting bolts. It's very easy to raise the engine with the help of a buddy. Are you dead-set on staying with aluminum?
I went to SS years ago after folding up enough blades in the trees to fill the back of my pickup with.
Don't let the Myth of "SS props will destroy your lower unit" get you...it's simply not the case.

Yes, I'm referring to the tilt pin, and that's the story I heard about the ss props, that they would wreck the lower unit if I hit something with them, otherwise, I'd take one in a heart beat, the log I hit wasn't very big and I backed way off the throttle as soon as I saw it and swerved trying to miss it but hit it anyway, it put a pretty good fold/dent in one of the blades, but not bad enough that it can't be straightened out, put a crescent wrench on it and bend it back out about 3 inches and it will be fine.

Now, about raising the motor, the cavitation plate (hope I spelled that right) is exactly even with the very bottom of the boat, not the keel, but the bottom of the boat, I think (I'm no expert) but I think the height is about right.

I'll get a better idea of where the motor is set exactly, and see if I can get a picture up here of what I'm talking about, and mabe some pictures of the back of the boat where the engine attaches.

 

[steelespike]

Re: 1978, Evinrude 115 replacement prop?

As far as the motor height the cavitation plate even with the bottom of the boat should be considered a starting point.Could end up signifigantly higher
and on some boats might be lower.Could result in higher speed,better holeshot and slightly improved economy.A stainless prop will make it possible to get the best setting.

 

[Mr.Stuart]

Re: 1978, Evinrude 115 replacement prop?

As far as the motor height the cavitation plate even with the bottom of the boat should be considered a starting point.Could end up signifigantly higher
and on some boats might be lower.Could result in higher speed,better holeshot and slightly improved economy.A stainless prop will make it possible to get the best setting.

I believe I have the engine itself dialed in as far as how well it runs, the drop in RPM could be maybe because of the bent prop? ...that's just a could be, or maybe I still have something out of whack with the throttle cable?

So, with that said, if I want to "dial" it in for optimum performance, where do I start? and what do I need to do to get my findings over here to you people? Pictures of the back end of the boat as it sits in the water when the engine isn't running? Pictures of the back of the boat while it's up on plane so you can see exactly where the lower unit is riding in the water, and what about this stainless steel prop verses aluminum? And the size and pitch, the 13x19 as far as I know is what has always been on it, and I believe that the spare prop I got with the boat is the same thing, how do you determine the best size, pitch, and or number of blades? I have read where it can be a hit and miss kind of thing, trying different props as you go, but I don't believe that I have the option of trying different props, don't know of any local places around here that would loan you a prop to try.

 

[walleyehed]

Re: 1978, Evinrude 115 replacement prop?

Beings I had the same rear-end on my boat with the 115, I can tell ya straight out, it will perform great with the engine lifted up to where the third set of holes from the top line-up with the holes in the transom.
If you use a set of 2" spacers to set the engine BACK, you can mount it in the 4th set of holes..should be the last set on that engine.
Idea is to get the lower unit up as far as possible without loosing water pressure, to lessen the gearcase drag. which allows a bit more speed which lifts the boat even more.....again less drag, but it takes a Good quality SS prop to run even this high. Speed may not be your goal, but look at this....with the engine being mounted all the way down, at a cruise of let's say 3700RPM and maybe 32-33mph.
If we lift the engine up as suggested and install a prop that will handle the extra height cause we got extra bite and we want to cruise at that 32-33mph range, NOW we're only turning say 3400 maybe 3500...Guess what?...your fuel milage just took a big jump up, yet we're propped for the same top-end RPM in either case.
Efficiency is the name of the game for total performance...and remember-performance is more than just speed..handling is great, ride is better, mpg is better and the smile on your face is from ear to ear.

 

[Dhadley]

Re: 1978, Evinrude 115 replacement prop?

One thing that caught me attention is that you say the motor doesn't idle below 1,100. That ain't right. Even if you're talking about it being in neutral. It shouldn't idle any higher than it takes to be at 650 +/- in gear. That should put it at about 850 in neutral.

1100 in neutral is real hard on the lower unit. Way harder than any ss prop will ever be.

 

[steelespike]

Re: 1978, Evinrude 115 replacement prop?

One thing that caught me attention is that you say the motor doesn't idle below 1,100. That ain't right. Even if you're talking about it being in neutral. It shouldn't idle any higher than it takes to be at 650 +/- in gear. That should put it at about 850 in neutral.

1100 in neutral is real hard on the lower unit. Way harder than any ss prop will ever be.

What He said!I read that and forgot to get back on it.Premature clutch dog
failure could be in your future.

 

[Mr.Stuart]

Re: 1978, Evinrude 115 replacement prop?

What He said!I read that and forgot to get back on it.Premature clutch dog
failure could be in your future.

ok, that 1,100 RPM may be a faulty Tach? I'm not sue I trust that instrument 100% when the tack says 1,100, it sure don't sound like it's running that fast, and doing all the adjustments I can do (or that I know of) that's as low as it goes, the only time I ever had a "pro mechanic" look at the boat was when I first got it, and I remember him doing an idle adjustment, he got it down to about where it's at now, then bumped it back up, and he made the comment that he didn't think the tach was accurate, and I do remember him trying to go for the 750 to 850 mark, so maybe that's where I need to start, find out what my true RPM readings are, so I know I have that part of it set right, then go from there? my thought would be that if it's reading high at low RPM's, then it's going to read high at high RPM's so 5,000, might be actually closer to maybe 5,200 or 5,300?

I know I'm doing a lot of guessing now, and this is supposed to be about props, but maybe I need to go back and take another look at the RPM readings

 

[Dhadley]

Re: 1978, Evinrude 115 replacement prop?

Make sure it's an OMC / BRP tach and it's set on 6. Yes, 6 - even for a V4.

 

[Mr.Stuart]

Re: 1978, Evinrude 115 replacement prop?

Make sure it's an OMC / BRP tach and it's set on 6. Yes, 6 - even for a V4.

The tach is the original Starcraft tach that came with the boat (it's got the Starcraft insignia on the face of it); I believe it was set up for that motor, so where is this setting at? On the back of the tach itself?

Everything is original with this boat, the outboard has been on it since new, it's lived it's entire life in a garage, so everything is in good shape, and it would be my guess that the tach that's in it was meant for that Motor, it seems to me that when you bought a Starcraft back then that took at outboard, it came with an Evinrude, and from what research I've done wit this boat, for the Holiday 18's (that's the model) they all came with the 115 HP outboard back then, so it would be my guess that the tach should have been a match for the motor, I may be wrong, but that would be my guess.

 

[walleyehed]

Re: 1978, Evinrude 115 replacement prop?

Yea, it may be the tach that came with it...that's why we say change it out for a new OMC/BRP (Johnson/Evinrude) tach. They are good in most cases, for about 5 years, as far as being accurate. The tach is the single MOST IMPORTANT instrument in the dash....we're concerned with the work the engine is doing....speed is directly a result of maximizing the set-up. We really only use speed for Prop slip ratio calculations-efficiency.
By all means, if you listen to any recommendations, please spend the 75$+/- for a new JohnRude tach.

 

[Mr.Stuart]

Re: 1978, Evinrude 115 replacement prop?

Yea, it may be the tach that came with it...that's why we say change it out for a new OMC/BRP (Johnson/Evinrude) tach. They are good in most cases, for about 5 years, as far as being accurate. The tach is the single MOST IMPORTANT instrument in the dash....we're concerned with the work the engine is doing....speed is directly a result of maximizing the set-up. We really only use speed for Prop slip ratio calculations-efficiency.
By all means, if you listen to any recommendations, please spend the 75$+/- for a new JohnRude tach.

Ok, I'll start with a new tach, I hate to see the original one go, everything matches in the dash, is there anyway to recalibrate these things? Or am I better off to just replace it?

 

[walleyehed]

Re: 1978, Evinrude 115 replacement prop?

To my knowledge, there is not a "practical" way to dial them in...Cost prohibative would be another way to put it.
Save the tach....run the boat just before you take it out...install new and test-run...new tach setting on back will be "6". Record idle RPM and wide open throttle rpm from both.....unless the rigging is "WAY" out of whack, I think you'll see a different reading.

 

[Mr.Stuart]

Re: 1978, Evinrude 115 replacement prop?

To my knowledge, there is not a "practical" way to dial them in...Cost prohibative would be another way to put it.
Save the tach....run the boat just before you take it out...install new and test-run...new tach setting on back will be "6". Record idle RPM and wide open throttle rpm from both.....unless the rigging is "WAY" out of whack, I think you'll see a different reading.

Ok, I can do that, the tach is easy to get to so it shouldn't be much of a problem, I'll start looking for a new tach, hope that's all the rpm problem is

 

[Dhadley]

Re: 1978, Evinrude 115 replacement prop?

If you have a good local dealer he should have a shop tach. They can install it quickly (just clams on a plug wire & battery) and run the boat. Compare to verify.