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bigbluepirahna

RPM too high at WOT

Question

bigbluepirahna

Looking for help. Have a 115 yam 4str with a 13x19 prop on it. Full throttle rpm's are like 6500. Guessing thats too high, right?

Would there be a way to reprop to bring this down, but without increasing low end trolling speed?

I like where it's at for speed just in gear for pulling crankbaits.

If theres a way to do it, what size, pitch, # blades, and material do you recommend?

Thanks....

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TurnUpTheFishing

Very interested in the answers you get. I purchased a boat with a yamaha 50hp fourstroke. At WOT and properly trimmed it will hit 7000rpms. I try to bring mine up around 6000rpms and level off there. Ive read that four strokes can be ran harder and that reps say its better to run them at higher rpms than lower ones, but I dont know for sure.

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bigbluepirahna

Mine is on a alumacraft 185 CS, so with only the 115, it's a bummer to not feel like can run at wot since it's a bit underpowered to start with for any long runs on bigger water.

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Kyhl

If it is an aluminum prop, you can swap to a stainless of the same size which should bring it down a couple hundred rpm from the lack of flex in the prop without changing the low rpm speed. Might even increase hole shot.

I'd talk to Jay Soderbloom about it first because he can also recurve the prop to take off another 100 or 200 again with little affect on the idle speed.

My recommendation, call Jay and probably switch to a recurved SS prop of the same size.

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harvey lee

I totally agree with Kyhl, call Jay at Soderbloom's as he can suggest what is needed to cure your issues.

Jay knows his prop's.

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Whoaru99

For a Yamaha F115, the rating is 115hp @ 5500 RPM, and a WOT RPM range given of 5000-6000. Generally speaking, you want to be at or near the top end of that range with your normal load, so 5700-6000.

Also, generally speaking, 1 inch of prop pitch equals roughly 150-200 RPM change. Since you need to come down about 500-600 RPM, you'd need to increase the pitch of your 19 by 2-3", so something on the order of 21-22" (or closest available).

But, to your point, increasing the pitch of the prop to drop WOT RPM almost certainly will increase your trolling speed if you can't throttle back more. There are trolling plates and such but never have used one.

EDIT: The other possibility is that your tach isn't reading correctly. I'd probably try to get that verified before you spend $$ on a different prop.

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bigbluepirahna

Thanks for all the responses thus far. I have an email out to Jay but havne't heard back yet.

Good point too 99 on the tach. It's going to be at the dealer tomorrow to check a livewell issue, so I can ask them about that.

I was out last night, tach was showing close to 7000 rpm when i opened it up, so i backed off a ways to be safe for now.

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bigbluepirahna

Tach was problem. They said a yammy wont ever hit 7k without cutting out first. A quick adjustment to some screw behind the dash and problem solved!

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