F300 Rpms too low?

[Footankleg]

I have 2016 F300s on a Cobia 296. My WOT is 5400 rpms at 54mph with moderate load ( full fuel, some gear, etc). I have tried many different props. I could not get more speed even with higher rpms.

I've been told that engine manufacturers have dialed back the ecu mapping and that newer motors are not full HP. My boat should turn 58-5900 rpms and 58-59mph with these props. PT OFS3x20p.

I can share prop test results.

My question is whether or not I could get shorter engine life by keeping props with wot 5400rpms? I am not making oil to my knowledge.

I do not want to drop pitch just to gain rpms as I will not gain speed and will lose the 1:1 rpms to speed and mileage I'm seeing. However, I will change props for more rpms if it is clearly better for the engines.

[cpostis]

I was trying to find out exactly what props you have. Looks like the PT OFS3x20P is manufactured by Powertech. From what I can tell, they don't manufacture props suitable for 300 HP V8 Yamahas. They do sell cheap, about $450 compared to Yamaha's discount price of about $600. I've said before that props of same diameter and pitch do not necessarily give you the same performance results.

I don't know who has been selling you these Powertechs, but I would be concerned about their performance on those 300's. Now I could be wrong.

Maybe you want to try the same props on the performance bulletin Boscoe posted (Yamaha Part # 6CE-45932-00-00 / 6CF-45932-00-00 ). Check that engine mounting height as well. The bulletin says "Mounting Hole Position #2". Don't know if your boat is exact as the bulletin though. Talk to someone experienced in props that sells them (Yamaha Five Star **** Dealer).

Good luck.

[pstephens46]

I wonder what the reason may be for the shortage.

[Footankleg]

Thank you for all of the replies. Maverick hewes pathfinder cobia uses Powertech props. The performance bulletin is certainly attractive but does not represent a boat set to go offshore (fuel, tools, gear, life raft, ice, etc).

I tried Merc thunderbolts, merc rev 4s, Yamaha ssii and Merc Ecos. No prop passed 54 mph. This was inland with full fuel and some gear, live wells full. The existing PTs had the best numbers. Check out the prop data attached. Note that the Rev4 17s were NOT WOT.

I'll double check the engine height. It sounds like I need to prop for 6k wot to protect engines.

[Footankleg]

Maverick boat group (mbg) acquired cobia maybe in 2006 or 2007. They kept the name only and designed boats from the ground up.

If you look at my numbers, I'll have to burn a lot more fuel and turn a lot more rpms if I prop to 6000k. When you are running over 100nm each way to the Bahamas, 1.4 vs 1.2 or 1.1 is a big deal.

[Footankleg]

Not necessarily. You might be turning more RPMs but your fuel burn might be less and thus your efficiency be higher.

People lose sight of what makes power. It is RPM and manifold pressure. MP in the form of throttle opening. Going down in pitch raises the RPM which lowers the manifold pressure for a given throttle setting. Less MP with the same RPM results in less fuel burn.

It is most desireable to prop to be at or near red line RPM at WOT. For a number of reasons, one being an increase in fuel efficiency at cruise RPM.

Please look at the data table I posted above. Don't you agree that my prop trials show worse efficiency with the lower pitched props? Note that the rev4 17s were NOT WOT. I did not push any further but could have.

[99yam40]

easier to read this way for some
also very misleading if you label it WOT and it is not.

strange how the PB Boscoe posted showed the motors in it running 5900RPM at 59 MPH with 15 X 20 SS props but you are not getting close to that with a 20.
what diameter is the one you tried?

[Footankleg]

All props were WOT except rev4 17s. The rev4 17s were not because they were way under pitched and I did not want to over rev. The ofs3 are 15.25x20. The table was posted with my iPad. Thanks for correcting the size.

[cpostis]

Sounds like you have been thorough in your analysis, but just to add to the conversation...

Could your inability to reach WOT RPM be other than prop selection? The Merc 4 props are four blade (the 17" maybe not so under pitched as you think?), the Powetech is 3. The props on the bulletin Boscoe posted (which reached WOT RPM and 59MPH) are 3 blade Yamaha SWSII 20P (same as the Yamaha you tried , except 1" pitch difference). Looking at your readings, I assume the others are all 3 blade as well? Looks like all are readings between them are what should be expected other than reaching WOT RPM.

I wonder what WOT RPM your engines will turn on a test props/wheels? Are your engines throttles opening completely?

[Footankleg]

Sounds like you have been thorough in your analysis, but just to add to the conversation...

Could your inability to reach WOT RPM be other than prop selection? The Merc 4 props are four blade (the 17" maybe not so under pitched as you think?), the Powetech is 3. The props on the bulletin Boscoe posted (which reached WOT RPM and 59MPH) are 3 blade Yamaha SWSII 20P (same as the Yamaha you tried , except 1" pitch difference). Looking at your readings, I assume the others are all 3 blade as well? Looks like all are readings between them are what should be expected other than reaching WOT RPM.

I wonder what WOT RPM your engines will turn on a test props/wheels? Are your engines throttles opening completely?

Interesting point. How do you check full throttle on fly by wire?

[cpostis]

Interesting point. How do you check full throttle on fly by wire?

I'm not familiar with your motor. Visually/physically, I'm not sure. But, I think perhaps on YDS (Yamaha Diagnostic System) you can monitor throttle valve opening in degrees 0-90? Maybe YDS can test sending a signal to open the valve from 0-90 degrees as well?

Here's a screen shot of an older version YDS not for your motor showing some monitoring functions.

[IMG]YDS.Screenshot.Monitor by Charles Postis, on Flickr[/IMG]

Others that are familiar with your engine control system and YDS should respond.

[Footankleg]

Thanks for the feedback. I can appreciate that propping to 6k can be better for the life of the engines. However, my prop test data disagrees with your assessment that I'll get better speed and mileage. My present props had the best stats. The props that achieved higher rpms clearly burned more fuel with some matching top end but not exceeding it.

[boscoe99]

This is America. They are your motors to do with as you wish.

Prop them to only get to 5000 RPM if that is what you want.

Run them at idle all of their lives or run them at WOT all of their lives. It does not matter.

[Footankleg]

This is America. They are your motors to do with as you wish.

Prop them to only get to 5000 RPM if that is what you want.

Run them at idle all of their lives or run them at WOT all of their lives. It does not matter.

I'm trying to educate myself and make the best decision I can. I started my reply with "thank you". I didn't intend to ruffle any feathers. My props are 5400 rpms wot. That is why I started this quest. Again, thank you for your help.

My post earlier today was specifically to this post "IMO you want more RPMs out of that F300. You'll get more speed at 6000 RPMs - better fuel economy at cruise, and overall better for the motor IMO." As I mentioned, yes better for the engines but more speed and economy no. Look at the swsii 19p. Same geometry but turned closer to target wot rpms. Cruised slower with decreased economy.

[99yam40]

Is the Performance Bulletin posted close to the rig you are running?
If so you should be getting close to that info if yours is rigged properly