evinrude 115 prop

[mstpierre]

I have a 1993 stratos 274fs with a 115 Evinrude on it.  The boat seems to preform best with a 13 3/4 x 15 prop on it.  It came with a 13 1/4 x 17 on it and it seemed "overpropped" according to the mechanic.  It runs great now.  Is there any reason I should experiment with other sizes?  He said the prop to buy would be $150.  Is this the prop I should have or are there more affordable brands out there?  Thanks a lot.  I know very little about propellers so any info would help.

[cart7t]

Your best bet is to go with a Stainless steel prop.  You might be able to find one used for $150.  

[mstpierre]

why is stainless so much better?

[cart7t]

More durable, less flex, better overall performance than aluminum.  

[Way2slow]

You want a prop that will let that motor turn 5,300 - 5,500 rpm with your normal load

Try to find someone that has a good 15" stainless and will let you try it.  That will remove any doubt as to why pay the extra bucks for one.

[mstpierre]

The dealer said optimum rpm is just under 6000 rpm per the manual.  With the prop that they put on it for me to "try", it maxes out at 5900 rpm.  They stated they feel this is ideal for this motor.

[Way2slow]

I'm affraid that dealer would have to physicaly show me what 1993, 115 manual he's looking in. I don't claim to be an expert but do know a little about motors. The crossflow motors (that's the type yours is) develop harmonics between approx 5,800 and 6,200 rpm that can greatly make you regret you ever ran it in that rpm range. I've never seen a crossflow that had a factory max recommended rpm above 5,700, and would be willing to make a wager your's is only 5,500. Just be sure you find you a good, spare powerhead if you keep running it in that range. The looper's run 6,000 rpm but not the Xflow's.

Now, with all that said, and they went to that small of a prop to get the rpm up, sounds like it might have been struggling a bit to get on plane. If that's the case, I would stongly suggest a compression test on the engine. Low compression is one of the main causes for poor hole shot. It doesn't hurt top end much but the drop in torgue it creates kills hole shot. If he told me it's suppose to turn 6,000 rpm, I wouldn't put much faith in anything else he told me. Compression might be fine, but would check it to be sure. I think a 115 on that size boat is touch on the small size.

[mstpierre]

So I dug out the manual and you are correct.  5500 should be the max.  Perhaps I should put the 13 1/4 x 17 back on to lower the rpm back down to that range.  This is actually a new powerhead so I know the compression is fine.  The engine may be a bit on the small side but it is what it is.  Would a hydrofoil help get up on plane quicker at all?  I got this boat for a fantastic price even after having to have the powerhead replaced.  I would have preferred a 150 but I will have to make the best of what I have.  

[mstpierre]

what would have been the original prop for this motor?

[Sfritr]

I have a 96 Stratos 278.  Mine is rated for a 150. I believe the max rating for that year 274 was 150hp also.  Original dealer mounted prop for that make and model was 14 1/2 X 23 1/2  I am pretty sure.  My buddy had that same model stratos

[Sfritr]

OOPS I meant 13 1/2 X 23 1/2

[mstpierre]

thanks.  I went to the shop and thier technical manual states up to 6000 rpm.  So I guess the repair manual splits the difference at 5500 rpm.  I have seen it now with my own eyes, as stated above.

[Way2slow]

Oh well, I tried.  There's no way in hell I would turn it over 5,700 but  it's your motor and I hope you get a long service life out of it, good luck.

[mstpierre]

I spoke with the mechanic and they said that the boat does pop out of the water better with the smaller propeller.  I went ou ton the lake and with the motor trimmed down all the way the boat is right at 5500 rpm with the smaller prop.  As I trim it up and get more speed, the rpm's increased closer and closer to 6000.  I didn't go much farther.  I do think the boat preformed well but I am not comfortable running it at or above the max rpm.  Should I put on the original 13 1/4 x 17 prop?  If I do could I gain any hole shot from this prop by using a hydrofoil?  This is really a mystery for me and I appreciate all the help I can get.  Thanks a lot.

[Sfritr]

IMO unless you are fighting for position in MANY tournament situations you would be better off with a larger prop.  You probably won't gain that much from a smaller prop and may save your motor in the process.  

I have a 96 Stratos with a 150 and my prop is a four blade 14 1/4 X 25.  I run at 5500 RPMs and feel very safe with its performance.  I have used my backup prop that is a 3 blade 13/12 X 24 and have much less control, less rpms, and some ventilation.  

GOOD LUCK  

[cart7t]

Seriously,  a 21p in a stainless should put you right in the ballpark RPM wise.  You'll gain some lower end bite on the holeshot getting away from that aluminum.  While I'm sure the aluminum 17" seems to be the way to go, you're way over the max, RPM wise for that motor.  

[mstpierre]

So, when I take the boat out with the original prop out if the max rpm trimmed up is 5500 then I should be ok.  If it still pushes up over the 5500 then I need to go larger?  Does the size 13 1/4 vs 13 3/4 matter?  Would a cupped propeller make a difference?  No one has mentioned what effect if any a hydrofoil would make.  

[cart7t]

There's a lot of great guys here that can help you.

BTW, hydrofoil type devices are meant to increase stern lift. They solve problems with boats that are stern heavy and have problems getting out of the hole and can be a remedy for boats that have porpoising issues due to stern weight or load problems.