Anyone running non-factory prop on R25/27 classic?

[NorthernFocus]

I'm contemplating re-powering our 2008/9 R25. As part of the exercise I've been studying prop alternatives for the engines I'm considering. And as part of that exercise I've been running the calculations vs historical performance of the boat. The boats have been around for a few years now so thought I'd ask what other real life experience people have gained.

So the question is simply per the thread title. Anyone running props other than the originally supplied 3-blade Acme? On the 25s the original wheels were either Acme 3-blade 17x15 or 17x14 both with 0.105 cup. Not sure but I believe the later R27s with the 200hp engine came with 3-blade 17x17 with 0.105 cup.

 

[Red Raven]

I had my prop on our R27 Classic re-pitched from the 3 blade 17x17 0.105 cup to 17x15.5 0.105 cup last winter because I could no longer reach the 4000 rated rpm (was only getting 3750). The boat seems much happier with the reduced pitch and runs at a lower temp though I think it now may be slightly under propped. Speed is a knot+ less (12kts) at 3400rpm but fuel burn is down as well. My max rpm lightly loaded is now 4150 and around 4050 with our typical gear. Pretty happy with it. The only thing I would add is for some reason it seems the RT boats get more increase in rpm for each reduction in pitch than expected. I was told to expect this from the ACME Propeller tech who said don’t overdo it. The local prop shop wanted to go to 15 inches as he expected 200 rpm increase for each inch in reduced pitch. I said I was more comfortable with16 based on ACMEs comment and we compromised on 15.5 with the promise he would re-pitch by .5” for free if needed. I still may have him make it 16 this winter when I pull the boat as I think that would be spot on.

IHTH,

Curt

 

[NorthernFocus]

I had my prop on our R27 Classic re-pitched from the 3 blade 17x17 0.105 cup to 17x15.5 0.105 cup last winter because I could no longer reach the 4000 rated rpm (was only getting 3750). The boat seems much happier with the reduced pitch and runs at a lower temp though I think it now may be slightly under propped. Speed is a knot+ less (12kts) at 3400rpm but fuel burn is down as well. My max rpm lightly loaded is now 4150 and around 4050 with our typical gear. Pretty happy with it. The only thing I would add is for some reason it seems the RT boats get more increase in rpm for each reduction in pitch than expected. I was told to expect this from the ACME Propeller tech who said don’t overdo it. The local prop shop wanted to go to 15 inches as he expected 200 rpm increase for each inch in reduced pitch. I said I was more comfortable with16 based on ACMEs comment and we compromised on 15.5 with the promise he would re-pitch by .5” for free if needed. I still may have him make it 16 this winter when I pull the boat as I think that would be spot on.

IHTH,

Curt

Thanks for the input. Interesting I spoke with two different prop shops and neither wanted to deal with the Acme wheel.

When I use realistic cruising weight and run prop calcs it always comes back with 18 in diameter and 12-14 in pitch. Also shows speed consistent with reality. 18 is getting iffy on tip clearance. Was hoping someone has tried it and could report on results.

 

[Red Raven]

Thanks for the input. Interesting I spoke with two different prop shops and neither wanted to deal with the Acme wheel.

When I use realistic cruising weight and run prop calcs it always comes back with 18 in diameter and 12-14 in pitch. Also shows speed consistent with reality. 18 is getting iffy on tip clearance. Was hoping someone has tried it and could report on results.

Here is what I got from Acme.
…
Hi Curt,

RE: 2014 Ranger Tug, Volvo D3-200, 4000 rpm, 2.03:1
Acme part # 1118 -- 17.00 X 17.00 VR3B 1.25 .105Cup
Originally owned the boat: 19.6 knots top end speed @ 4040 rpm WOT
And then lost rpm over the years.

Acme # 1118 – True 17” dia., but it’s a varied pitch distribution and the overall average pitch is approx. 16.3”

r/R​	r​	Pitch​
0.4​	3.400​	16.8143​
0.5​	4.250​	17.0000​
0.6​	5.100​	16.9735​
0.7​	5.950​	16.7576​
0.8​	6.800​	16.3705​
0.9​	7.650​	15.8250​
0.95​	8.075​	15.4959​

Cup heights below are from the .4 radii to the .95 radii, respectively:

0.0000​

0.0277​

0.0704​

0.1050​

0.1050​

0.0695​

0.0456​

Enter Rated RPM​	4000​
Enter Gear Ratio​	2.03​	TO 1
1" OF PITCH IS =​	108​	RPM
​	​
0.03" OF CUP IS =​	59​	RPM
change in rpm at WOT​	​

But be careful with these calculations. In other words, maybe begin by cutting value in half.

Never mess with the tip cup. Do not change tip cup.
Max. cup is between the .7 & .8 radii… When adjusting cup focus primarily on this area (and adjust / blend outside of this area to maintain a smooth transition in the trailing edges of the blades).

If you were going to order a new propeller, you would probably consider a # 1304 --- 17.00 X 16.00 VR3B 1.25 .105Cup (Varied pitch distribution – actual overall average pitch = approx. 15.34”

Thank you,

Jim Thelen
Sales Engineer
Acme Propellers
3501 Fruitridge Ave NW
Suite A
Walker, MI 49544
O: (888) 661-2263 ext. 106
E: jthelen@acmemarine.com
W: www.acmemarine.com
…

Acme uses a variable distribution pitch which is possibly why your prop shops want to avoid it. I originally went to Olympic propeller in Anacortes and they said they could not change the pitch only the cup. I tried that and was unhappy with the results (too much slip). Acme recommended The Prop Shop in Mukelteo. They were able to change the pitch no problem but could not maintain the variable distribution (I.e., the pitch is now constant through the radius).

 

[NorthernFocus]

Here is what I got from Acme.
…
Hi Curt,

RE: 2014 Ranger Tug, Volvo D3-200, 4000 rpm, 2.03:1
Acme part # 1118 -- 17.00 X 17.00 VR3B 1.25 .105Cup
Originally owned the boat: 19.6 knots top end speed @ 4040 rpm WOT
And then lost rpm over the years.

Acme # 1118 – True 17” dia., but it’s a varied pitch distribution and the overall average pitch is approx. 16.3”

r/R​	r​	Pitch​
0.4​	3.400​	16.8143​
0.5​	4.250​	17.0000​
0.6​	5.100​	16.9735​
0.7​	5.950​	16.7576​
0.8​	6.800​	16.3705​
0.9​	7.650​	15.8250​
0.95​	8.075​	15.4959​

Cup heights below are from the .4 radii to the .95 radii, respectively:

0.0000​

0.0277​

0.0704​

0.1050​

0.1050​

0.0695​

0.0456​

Enter Rated RPM​	4000​
Enter Gear Ratio​	2.03​	TO 1
1" OF PITCH IS =​	108​	RPM
​	​
0.03" OF CUP IS =​	59​	RPM
change in rpm at WOT​	​

But be careful with these calculations. In other words, maybe begin by cutting value in half.

Never mess with the tip cup. Do not change tip cup.
Max. cup is between the .7 & .8 radii… When adjusting cup focus primarily on this area (and adjust / blend outside of this area to maintain a smooth transition in the trailing edges of the blades).

If you were going to order a new propeller, you would probably consider a # 1304 --- 17.00 X 16.00 VR3B 1.25 .105Cup (Varied pitch distribution – actual overall average pitch = approx. 15.34”

Thank you,

Jim Thelen
Sales Engineer
Acme Propellers
3501 Fruitridge Ave NW
Suite A
Walker, MI 49544
O: (888) 661-2263 ext. 106
E: jthelen@acmemarine.com
W: www.acmemarine.com
…

Acme uses a variable distribution pitch which is possibly why your prop shops want to avoid it. I originally went to Olympic propeller in Anacortes and they said they could not change the pitch only the cup. I tried that and was unhappy with the results (too much slip). Acme recommended The Prop Shop in Mukelteo. They were able to change the pitch no problem but could not maintain the variable distribution (I.e., the pitch is now constant through the radius).

Thanks for the detailed reply/info. Acme really shook things up in the industry by using CNC machining to manufacture wheels. They put the complex geometry into the wheel for efficiency but it's somewhat moot if you're running around 50 percent slip as many of us are when running our Rangers heavily loaded. Or at hull speed.

As I understood from the shops I spoke with they didn't want to deal with the NiBrAl. They said it's very difficult to bend it precisely as it has a tendency to spring back.