will ss prop increase rpm's

[redlinj]

Hi, my Grady White Tournament 22 is presently running a 19" aluminum prop. Recommended wot for the 485 engine is 4200-4600. With just myself in the boat I can attain 4200 rpm's which is obviously the low end of the range. I'd like to gain that additional 400 rpm's. I have a Michigan Wheel Rapture ss prop with the same 19" pitch and a diameter of 14.25. Would this ss prop be a help in raising the rpm's to the upper end of the range?

 

[Bondo]

Re: will ss prop increase rpm's

Hi, my Grady White Tournament 22 is presently running a 19" aluminum prop. Recommended wot for the 485 engine is 4200-4600. With just myself in the boat I can attain 4200 rpm's which is obviously the low end of the range. I'd like to gain that additional 400 rpm's. I have a Michigan Wheel Rapture ss prop with the same 19" pitch and a diameter of 14.25. Would this ss prop be a help in raising the rpm's to the upper end of the range?

Nope,.... 19"s is still 19"s....

 

[QC]

Re: will ss prop increase rpm's

May even make it worse. Do some reading here on SS vs. Aluminum. Good Luck!

 

[pokman]

Re: will ss prop increase rpm's

i had a aluminum 16p black max and put on a 16p ss vengeance same dia. And i gained over 100rpms and 1mph. Also tried a 16p turbo prop and couldn,t even run it wot because i was over my max rpm without even trimming. Seems in most cases you would lose rpms with the switch from ss to aluminum, but i would try it out at least may get lucky.

 

[jestor68]

Re: will ss prop increase rpm's

I'm with QC on this one; in that (usually) the SS prop of similar design and size will operate with greater efficiency. This typically results in a slight decrease in rpm, accompanied by a moderate increase in speed.

As Pokman points out; it's possible to get hold of a poorly designed SS prop; in which case, all sorts of strange things can occur.

 

[theBrownskull]

Re: will ss prop increase rpm's

It will probably go down in rpm's but it doesn't hurt to try. All props are different and you never know what you will get.

 

[redlinj]

Re: will ss prop increase rpm's

I certainly appreciate the input. Since I have to pull the boat out to install a new transducer I'll change to the ss 19". If that doesn't work, then I will go to a 17". What if that takes it over it's max of 4600 rpm's----do I just run keep it 4600 or less?

 

[steelespike]

Re: will ss prop increase rpm's

It sure won't hurt to try the ss 19.results will depend partly on how well the al prop is doing.
if the al prop has a lot of slip the ss may lower rpm but the improvement in slip may help speed
also if it has more lift it may help speed. there could be a slight across the board overall improvement
that could make it more enjoyable to use if the motor can make rpm.
If it does over rev just throttle back a little.

 

[redlinj]

Re: will ss prop increase rpm's

OK, this could be a major break thru!!!!!!!---Pulled the boat out and removed the prop. It came off quite easily. Tried the 14.25 x 19 Michigan Wheel Rapture ss prop but it wouldn't fit---hit the trim tab/anode fin. So, put on the 17"(diameter I'm not quite sure of) it fit like it should. Boat back in water, headed out for a test run. Dammmm----still 4200 rpm's at wot. Major disappointment! Get home and check out the original prop. Guess What! It's a 14 x 19 stainless prop covered with a rather course black matt finish. My theory is that this rough rhino coating had caused enough resistance to account for the missing3-400 rpm's. I'll shine it up and put it back on. Gentlemen, please, your thoughts! Oh, I've only had the boat for 6 weeks and I also did get the transducer on.

 

[90stingray]

Re: will ss prop increase rpm's

Should get you your r's back. But if not, or just for fun, you can get an offset tab and run that other prop you already have... which obviously has more rake... Which might get you some more mph at the same rpm. And that's a good thing.

 

[redlinj]

Re: will ss prop increase rpm's

Well, I've certainly learned some interesting facts--like off set tabs and also that you can grind down the tab for clearance and that on a boat with power steering, you may not even need a trim tab, just a flat anode. It will probably take me a few days to make the changes but when I do I will certainly let you guys know. Thanks

 

[Bondo]

Re: will ss prop increase rpm's

OK, this could be a major break thru!!!!!!!---Pulled the boat out and removed the prop. It came off quite easily. Tried the 14.25 x 19 Michigan Wheel Rapture ss prop but it wouldn't fit---hit the trim tab/anode fin. So, put on the 17"(diameter I'm not quite sure of) it fit like it should. Boat back in water, headed out for a test run. Dammmm----still 4200 rpm's at wot. Major disappointment! Get home and check out the original prop. Guess What! It's a 14 x 19 stainless prop covered with a rather course black matt finish. My theory is that this rough rhino coating had caused enough resistance to account for the missing3-400 rpm's. I'll shine it up and put it back on. Gentlemen, please, your thoughts! Oh, I've only had the boat for 6 weeks and I also did get the transducer on.

Ayuh,.... If ya went from a 19" SS prop, to a 17" aluminum prop, 'n it didn't pick up any rpms,...

I'd be wonderin' if the Motor is pullin' up to it's potential....??....

 

[redlinj]

Re: will ss prop increase rpm's

compression is 155 on all cylinders give or take a few pounds. I'm hoping the engine IS pullin' up to it's potential. I'll find out soon.

 

[QC]

Re: will ss prop increase rpm's

and that on a boat with power steering, you may not even need a trim tab, just a flat anode.

Not may not need; do not need . . . Not on Bravos or Alphas with power steering straight out of factory.

 

[redlinj]

Re: will ss prop increase rpm's

Well then, here's what I'm thinkin'. Grind down the trim tap so the "Rapture 14.25 x 19 will fit and see what happens. That sounds easier that trying to get all that gook off the original 14 x 19 ss.

 

[redlinj]

Re: will ss prop increase rpm's

So, the 17"pitch aluminum prop kept me at 4200 rpm's with about the same speed. Replaced it with the 14.25 x 19 Rapture and actually got more speed, but lost 400 rpm's. Cleaned all the gook off the original 14 X 19 ss prop but that didn't really help---still 4200 @ 30 mph. I know the tack is accurate. Could it be a fuel/carb thing ? With the engine putting out 155 or so on each of the cylinders, it seems like it should have enough power. Am I making too much out of this 4200 rpm's with 1 person and half tank of gas with a 14 x 19 prop. Should be 4200-4600 at WOT.

 

[QC]

Re: will ss prop increase rpm's

How do you know the tach is accurate? Also, what speed for the Rapture 19 and at what RPM? I calc'd a 1.84 ratio and 32 MPH and 3850 RPM and got 15% slip. All seems "right" as far as the math is concerned. There are a few possibilities:

1) This is all she's got and you need to play around with props until you get it right. This is only around 160 hp at the prop so not going to be real fast no matter what.

2) There are engine issues. Tune, timing, fuel, etc.

3) Some or all of the numbers are bogus.

4) The bottom is dirty, or you are not trimming right, or there is a drive issue (doubtful).

5) A combination of some or all of the above (likely)

 

[redlinj]

Re: will ss prop increase rpm's

Hit 30 mph on gps with the Rapture @ 3800 rpm's. A loss of 400. Gave the boat a tune up after getting it. Engine would only get to 3900 rpm's. ----- but the timing was off 4 degrees. Re timed and gained 300 rpm's. Took it out last night on a calm and quiet Lake Erie. Four people, 3/4 tank of gas and the original 14 x 19 cleaned up prop and got 24 mph at maybe not quite 4200 rpm's. Earlier in the day, with 2 people, and the same amt of gas and same prop, we went 4 mph faster. Same 4200 rpm's. Saying that I know the tach is accurate is perhaps a bit erroneous as I've not had it tested. What I should have said was that at one time with a spun hub, the tach went to 5500 momentarily, so I know it will go higher and not just top out at 4200.

 

[QC]

Re: will ss prop increase rpm's

I need to qualify this with an "I always say that", but you need to verify the tach . . .

 

[redlinj]

Re: will ss prop increase rpm's

Supreme Mariner, I hate to say this, but you are absolutely correct. No emperical study can be done based on theory or hearsay. Now if I can only find the correct tools for the job, I'll get started. Thanks.