# Opinions dialing in a new prop



## Hardluk81 (Jan 3, 2016)

I just ran my new PT SRA3 and am about 450-500 RPM over. The prop slips a little when I get on it hard getting out of the hole but doesn't if I slowly ease into it. This is something my factory prop didn't do and thought the new one would be even better out of the hole considering how worn the old one was. There is very little chatter at idle when in gear but if I barely give it gas it goes away so nothing I'm concerned about. Every thing else i like about it (cornering, speed, bow lift etc.) The question is what would you do to get the RPM down add more cup or swap it out for the next size up? The only thing concerning me about going up in pitch is it will still slip out of the hole. Also I don't know if I can makeup for 450-500 RPM with cupping.


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## RunningOnEmpty (Jun 20, 2015)

I personally like a little slip when getting up on plane. My theory is it allows the motor to get into it's power curve faster.


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## Vertigo (Jun 3, 2012)

If you have work done on the prop and the problems still exist, too bad, you won't be able to swap it out with Powertech. OTOH, if you swap props, and you still have problems, you'd still have the option to do work on the prop or swap it again. I'd say keep your options open.


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## No Bait / Lures Only (Apr 10, 2011)

RunningOnEmpty said:


> I personally like a little slip when getting up on plane. My theory is it allows the motor to get into it's power curve faster.


My PT SRA does exactly the same, you should keep the prop for quicker hole shot and load carrying ability the extra rpms provide. Once you kill the extra rpm with cup or pitch change the load carrying ability will be reduced and your rpms will be below the horsepower rpm range motor is rated. My 25 2 stroke is 19" high on a 16" transom offset with a 4" jackplate. Ran 3 props all performed differently, turbo hot shot 12" 6500+ hit rev limiter 34-35 but terrible blowout and handling. PT SRA3 12" 5850 Runs great and handles, no blowout 32-33. Solias 13" too much pitch 29-30...


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## RunningOnEmpty (Jun 20, 2015)

stephenchurch said:


> My PT SRA does exactly the same, you should keep the prop for quicker hole shot and load carrying ability the extra rpms provide.


Mine always slipped a little on the hole shot because I run my motors as high as possible. The SRA is very impressive when it comes to running skinny.


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## Hardluk81 (Jan 3, 2016)

Well I guess I might call tomorrow and swap the 11p for a 12p since all of you say slipping out a little on the hole shot isn't that bad. In regards to keeping the 11p for extra power when I might need it, I was just trying to squeeze the last bit of performance out of her. I ran the boat about as loaded as it would normally be. If anything it would probably be a slightly lighter 3/4 of the time. Im just not sure if moving up to a 12p would be too much of a jump at only 500RPM over. I was trying to get as many opinions as I could before shipping these things back and fourth at $35 a pop, but Vertigo makes a good point.


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## RunningOnEmpty (Jun 20, 2015)

I" of pitch should be around a 200 rpm difference. What's the maximum rated rpm for your motor? All the new motors have a rev limiter. My suzuki df25a was a dog if I didn't allow it to spin up to it's max rpm's. Are you using one of those cheap mini tachs that seem to very?


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## Vertigo (Jun 3, 2012)

If you need prop slip to get your motor up to speed, you're probably running too small a motor. If the prop slips because it's too high or tilted too much, that's a different situation. If you have a jack plate the solution is simple. Lower the plate (move it down a hole or two) until there's little or no slip with a good hole shot and the motor full down. Tilting the motor in will also help. A slipping prop will never give the best hole shot.


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## tjtfishon (Feb 9, 2016)

RunningOnEmpty said:


> I" of pitch should be around a 200 rpm difference. What's the maximum rated rpm for your motor? All the new motors have a rev limiter. My suzuki df25a was a dog if I didn't allow it to spin up to it's max rpm's. Are you using one of those cheap mini tachs that seem to very?


11p to 12 p will be more than 200 rpm. That rule of thumb works for higher pitched props, but on these small outboards, 1" of pitch is nearly 10% change and in this case will likely lower RPM close to 500


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## firecat1981 (Nov 27, 2007)

tjtfishon said:


> 11p to 12 p will be more than 200 rpm. That rule of thumb works for higher pitched props, but on these small outboards, 1" of pitch is nearly 10% change and in this case will likely lower RPM close to 500


Where did you get that info from? My experience was closer to the 200rpm as quoted. I went through 5 props on my last few skiffs using the same motor and each pitch was between 150-300rpm max.


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## tjtfishon (Feb 9, 2016)

firecat1981 said:


> Where did you get that info from? My experience was closer to the 200rpm as quoted. I went through 5 props on my last few skiffs using the same motor and each pitch was between 150-300rpm max.


Well, it is math really, but here is a calculator. Theoretical would say closer to 500, but all variables can't be controlled, so real world with different slip could be closer to 400, but with a 11p/10p change he should see at least a 400 rpm difference.

http://www.csgnetwork.com/marinepropcalc.html


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## firecat1981 (Nov 27, 2007)

I've seen that calculator before, but it is nothing to be relied upon especially in smaller motors imo. It's better to look for a similar manufacturers test to compare to.


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## Vertigo (Jun 3, 2012)

Math is nice and precise, but the variables in the real world sometimes make the results of plugging in a formula unrealistic. Although the calculated rpm might drop between 400 and 500 going from 10 to 11 pitch, if the 11 pitch prop has less slip at the same speed, the rpm change could be considerably less than 400.


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## Hardluk81 (Jan 3, 2016)

Yes I have a TT on it. I've been running it for a while and think it's pretty close to dead on. The motor mounted where it is may be causing the slipping but I don't want to move it lower. The slipping isn't so bad that its stopping me from getting on plane or taking me a long time to do it. Also it's a 25hp 2smoke on a a 14' skimmer so it's not under powered.


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## Sublime (Oct 9, 2015)

I'd throw some cup on it, but that is just me. What happens when you wear the current prop down a little? It will just intensify the issues you are having now, (there is nowhere to go but down form here). Adding some cup will help with the slip and rpms and then as it wears down you end up back where you are now which is bearable.


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## RunningOnEmpty (Jun 20, 2015)

#2 cupping on the sra runs nice. I only paid $40 to get one done.


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## Hardluk81 (Jan 3, 2016)

I talked with PT today on the phone. He said to try the 12p first just to rule it out because once I change the one I have the warranty is voided and I can't swap it anymore. On the other hand I think I can accomplish what I'm looking for with some more cupping added to the one I ordered (11p) but will try a 12p just to rule it out. If I do decide later to go back with the 11p and add more cup is there a shop anyone recommends? I've looked online for a local shop (Jax) but looks like I'll have to send it off to get it done.


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## RunningOnEmpty (Jun 20, 2015)

Are you running the yamaha 2 cylinder? If you had the merc 25hp with the 2.25.1 gear ratio a 13p would be about right for the skimmer.


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## Steve_Mevers (Feb 8, 2013)

Just FYI. We used to have props ventilated (holes drilled on side of prop to let exhaust cause slip) so that the RPM would get high before the prop would grip the water. The idea was that it would get the RPM high before the prop gripped so that it would allow for better hole shot.


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## Hardluk81 (Jan 3, 2016)

It's a yami


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## Hardluk81 (Jan 3, 2016)

Just an update in case someone searches this thread for info later. I ran the 12p this morning and the RPM is now only about 200 over loaded with gear and two people. I'll probably just keep this one and maybe add some cup later once the warranty has expired. I could probably run a 13p but am not gonna pay another $55 to swap them again.


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## Skiff Junky (Oct 6, 2015)

Hardluk81 said:


> Just an update in case someone searches this thread for info later. I ran the 12p this morning and the RPM is now only about 200 over loaded with gear and two people. I'll probably just keep this one and maybe add some cup later once the warranty has expired. I could probably run a 13p but am not gonna pay another $55 to swap them again.


I don't see where you tell us what hull your running.

Back when I used to do this, the common prop for Yami 25hp 2 smoke on a Gheenoe Classic or LT was SRA 12p (3 or 4 blade) with standard cup or for those with jack plates SRA 4 blade 11p with a special ordered heavy cup. We dropped to 10p for heavy loads and even 9p with heavy cup for those who would pull skiers.

RPM can easily change 200 to 500 rpm per pitch change on these little motors as every little variable has a much bigger effect on these little skiffs. One of the biggest factors was when people switched blade design and didn't realize how much of a factor the blade design changed things. You have to factor blade design (surface area, leading edge and rake), pitch and cup. I had a rule of thumb that if I double cupped an SRA, I dropped the pitch 1 point and it would put me right where I needed to be. But your hull may differ.


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## Hardluk81 (Jan 3, 2016)

Sorry I didn't notice, that would help. It's a 14'6 Skimmer Skiff w/ a Yami 2s.


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## Preston904 (Sep 9, 2016)

Dang so you got a lot of RPM out of a 12p then if your at 6200. I have a skimmer 14 as well with an 09 2 stroke yami.
It turns 5980 at 31.2 mph with the stock 11 1/4 aluminum prop. I was worried about going to the SRA 12p thinking it would drop be down.


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## Skiff Junky (Oct 6, 2015)

Preston904 said:


> Dang so you got a lot of RPM out of a 12p then if your at 6200. I have a skimmer 14 as well with an 09 2 stroke yami.
> It turns 5980 at 31.2 mph with the stock 11 1/4 aluminum prop. I was worried about going to the SRA 12p thinking it would drop be down.





Preston904 said:


> Dang so you got a lot of RPM out of a 12p then if your at 6200. I have a skimmer 14 as well with an 09 2 stroke yami.
> It turns 5980 at 31.2 mph with the stock 11 1/4 aluminum prop. I was worried about going to the SRA 12p thinking it would drop be down.


The go to prop for that motor is an SRA 12p 3 blade with a light load. That's where I always started.


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