SS prop vs same size alum ?

[Hokie 59]

Anybody have any experience changing props on a 2004 F115 from the stock(?) aluminum prop (13 1/4 x 17) to an Apollo stainless steel prop, same size.
With the alum prop, WOT was about 6000rpm and about 30 mph in my Cobia CC 194. Now with the SS prop, WOT is 5400 rpm and 34 mph, same boat loading.
Question: Am I lugging the F115 too much or should I try a lower pitch SS prop - maybe a 13 1/4 x 15 ?

[boscoe99]

Yes. You are now lugging the motor. Not sure where you are located but come July/August the air will be hotter and more humid. You will lose HP and the WOT RPM will be even less than it is now.

Yamaha's recommendation is to have the motor propped so that at WOT, with the boat loaded, and the motor trimmed up only to the most efficient trim angle, the RPM is at or near 6000.

I would suggest that you try the same brand and model of propeller but with two inches less pitch. If you change brand or model then all bets are off as to what the results may be.

[99yam40]

usually when switching from alum to SS or the other way there is a change in prop pitch.

SS is stiffer and can be thinner and usually has more cupping

[Jason2tpa]

Interesting and surprising he lost as much as 600 rpms just by changing the props metal.

[boscoe99]

When going from aluminium to stainless, or vice versa, it is almost always much, much more than the metal or the metal thickness that changes.

I can't think of a single propeller maker that offers a specific model/style/etc. that has the exact same blade geometry in SS as in AL.

Just changing from one model of SS to a different model of SS, within the same brand, can cause the performance to vary wildly.

Changing propellers and anticipating performance can cause folks' hair to fall out. It is much more of an art than a science. Then too, what one folk wants from a propeller may be vastly different than what a different folk wants, even with the exact same boat and motor.

[Jason2tpa]

Changing propellers and anticipating performance can cause folks' hair to fall out. It is much more of an art than a science.

You got that right bossman.

[Hokie 59]

SS prop vs same size alum?

Thanks "Boscoe99".
So now I'm off to see how I can trade this shiny new SS Apollo 13 1/4 x 17 for a similar SS 13 1/4 x15. Don't know where to do that, but will search.
I started off with a 19" pitch Apollo, and that was "way-over" propped. I thought the same size as the AL would be just right - Not! So live and learn.
Any thoughts on how to trade this new prop for a 15" prop.

[boscoe99]

Thanks "Boscoe99".
So now I'm off to see how I can trade this shiny new SS Apollo 13 1/4 x 17 for a similar SS 13 1/4 x15. Don't know where to do that, but will search.
I started off with a 19" pitch Apollo, and that was "way-over" propped. I thought the same size as the AL would be just right - Not! So live and learn.
Any thoughts on how to trade this new prop for a 15" prop.

See if whomever you bought it from will let you return it for a lower pitch. Some dealers will and some won't. Some might want to impose a small fee but that might be preferable to selling it on the open market. In which case it might take lots of time to find a buyer and you will probably take a bigger financial hit.

[zenoahphobic]

Interesting and surprising he lost as much as 600 rpms just by changing the props metal.

He didn't loose 600rpm, he gained more thrust (4mph)!
He will thus expect (all things being equal - but they never are) even more by dropping down a pitch IN THE EXACT PROP.

Whatever happened to that recent thread ?

[Jason2tpa]

Thanks "Boscoe99".
So now I'm off to see how I can trade this shiny new SS Apollo 13 1/4 x 17 for a similar SS 13 1/4 x15. Don't know where to do that, but will search.
I started off with a 19" pitch Apollo, and that was "way-over" propped. I thought the same size as the AL would be just right - Not! So live and learn.
Any thoughts on how to trade this new prop for a 15" prop.

Man too bad you don't need a higher pitch prop or I'd trade with you. I've got the same make and diameter prop as yours, mine a 21". I also need to reduce pitch, but pains me to go out and buy a new one when the one I have is like brand new. Please let us know if you come across a trade dealer.

[panasonic]

He didn't loose 600rpm, he gained more thrust (4mph)!
He will thus expect (all things being equal - but they never are) even more by dropping down a pitch IN THE EXACT PROP.

Whatever happened to that recent thread ?

So looking at Yamaha f115 owners manuAL and it says WOT range is 5000-6000 rpm with max HP reached at 5500.

So the OP says he gained 4 mph at 5400 rpm with the change of prop. How can this be lugging the engine?

It is operating within the manufacturer specs and it is at essentially right at max spec rpm/hp. I would suspect he may gain a little better fuel economy at that rpm as well?

[boscoe99]

So looking at Yamaha f115 owners manuAL and it says WOT range is 5000-6000 rpm with max HP reached at 5500.

So the OP says he gained 4 mph at 5400 rpm with the change of prop. How can this be lugging the engine?

It is operating within the manufacturer specs and it is at essentially right at max spec rpm/hp. I would suspect he may gain a little better fuel economy at that rpm as well?

The owner's manual says to be in the upper half of the RPM range with the boat loaded and throttle wide open. 5400 is below the middle of the RPM range. Being in the upper half of the range would be 5501 RPM and up. Closer to 6000 RPM the better.

The OP's F115 does not have a knock sensor. That motor is susceptible to detonation of cylinders number 2 and 3. All the more important for that particular model to be slightly under propped, definitely not over propped.

[boscoe99]

From the Yamaha tune up specifications book.

[panasonic]

The owner's manual says to be in the upper half of the RPM range with the boat loaded and throttle wide open. 5400 is below the middle of the RPM range. Being in the upper half of the range would be 5501 RPM and up. Closer to 6000 RPM the better.

The OP's F115 does not have a knock sensor. That motor is susceptible to detonation of cylinders number 2 and 3. All the more important for that particular model to be slightly under propped, definitely not over propped.

That is an excellent explanation...I understand it much better now.

Thank you very much.

[Jason2tpa]

Boscoe, panasonic....in my boat, fully loaded, WOT, i can reach btwn 4800-4900, light load 5000-5100. Spec for my engine is 4500-5500. 21" pitch.

I should decrease. And i know propping is an art form, but what's yall's best guess to decrease...down to 19" or 17"? Consider i run the boat majority of the time loaded. Speed isn't a concern, whether i gain or lose a few mph, optimum engine performance is.