Considering new props Advice appriciated

[Fl_Richard]

Currently I'm running 14.5x19 stainless on counter rotating twins. My current economy is 1.75-1.80 nMPG at 3200rpm, 1.6nMPG at 3800rpm and 1.2nMPG at 5800rpm. Would changing to 14.5x20 have a significant impact on performance or economy?

Many thanks,

Richard

1) Performance issue you are trying to correct.
- Economy Improvement

2) Current prop manufacturer, model, aluminum or stainless and as a minimum.
- 3-blade Stainless Steel OMC P/N 389924 and it's counter rotating match

3) Current prop diameter and pitch (required).
- 14.5 x 19

4) Wide open throttle RPM and speed with an average load (very helpful)
- 5800 RPM 43 knots - 5500lbs - guestamate


5) Engine/drive make, model, year, and HP
-Johnson J150EXOM & J150NXOM 1995 150HP

6) Boat make model, year, length and weight
-Wellcraft 1995 Coastal 238 25.5 LOA 5500 lbs (guestimate)

 

[QC]

Re: Considering new props Advice appriciated

Well . . . hmmmmm. The best answer is maybe. You've got good data it appears and what you are seeing in results seems reasonable.

I find your recommended WOT RPM to be 4500 - 5500 which would indicate you should go up in pitch. However . . . I see the 2-stroke guys recommending higher than suggested RPM often, so we should hear what they have to say.

If you do not have a spare prop for each engine you need to do something anyway. If spares are not needed, and your motivation is economy, then I am not sure you'd get your money back very soon if ever . . . How much fuel do you burn a year? Figure you'll maybe save 1.724%, OK, be aggressive and consider that you'll save 2%. Start there for any savings. Takes a long time to pay for anything with 2% annual fuel savings. At 1000 gallons a year (very high) and $3 per, that's a whopping $60 per year in potential savings to pay back two $300 props . . . My head says 10 years for a simple ROI. Be exceptionally optimistic and figure 5% savings, that sounds like 4 years.

 

[hwsiii]

Re: Considering new props Advice appriciated

Richard, dhadley can give you better advice on what your motors should be turning at WOT, but to attain 5,400 RPM you would use a set of 21" props in exactly the same model prop you are using now, and you should pick up about an additional 1 to 2 MPH in top speed. But if it is not hurting the motors over revving them then you can stay with what you have. YOU did an exellent job of reporting the information for your boat that we need to help you.

H

 

[Dhadley]

Re: Considering new props Advice appriciated

You're fine at 5800 with those motors. The advantage to switching might be getting something with more lift to reduce drag. An awful lot depends on what you're looking for. The one thing that comes to mind would be going to the Turbo Ultima 4s to make gains in the cruise range without sacraficing top end. You're set up pretty well now at about 13% slip.

 

[Fl_Richard]

Re: Considering new props Advice appriciated

DH if I was to switch to the Turbo Ultima 4 what would be an equivelant pitch and diameter to use?

 

[Dhadley]

Re: Considering new props Advice appriciated

If you were planning on raising the motor then I'd try to make the 19's work. If we're going with the current set up the 17's would be a good choice. I like to go with the less of the two pitchs when faced with a choice like this. It's much more desirable to add bite - if needed - than reduce bite.

 

[Fl_Richard]

Re: Considering new props Advice appriciated

Thank you!

Richard

 

[Dhadley]

Re: Considering new props Advice appriciated

No problem. Let me know if you need help finding a set.

 

[Fl_Richard]

Re: Considering new props Advice appriciated

This may be an old thread but I'ts my old thread

Still looking at new wheels but now my oldies are another year or so older.

Looking at the OMC Propeller E/J Rebel [763571] and it's CR twin. Found online for $265.00 each and compelling...

Should I be looking for the Turbo Ultima 4s??? - hate to throw away valuable cash on wheels that wont work.

DH I'm not saying they wont work but the 3blade x 19 pitch seems "safer". I don't have any problem purchasing based on your experienced recommendation but I want to endure I get it right the first time.

Many thanks,

Richard