3 blade to 4 blade aluminum on 26' cruiser

[wrench 3]

For any one who might be interested. Midle of last sumer I replaced the three blade 19 pitch aluminum prop on our 26' aft cabin with a 454 magnum on an alpha drive, with a 17 pitch four blade aluminum.
The RPM at cruising dropped by 300. It gets up onto plane in 2/3 the time. Top speed went from 38 MPH to 44MPH. I don't have a read on the fuel consumption yet.
My suplier said he has had similer feed back from others. He also said that with 330 hp I should be using a stainles prop, but it's out of my price range.

 

[jestor68]

Re: 3 blade to 4 blade aluminum on 26' cruiser

Testing of a Solas 4 blade prop on my boat achieved similar results, except for a slight loss of top end speed. But since I never run wide open, the benefits of faster acceleration, the ability to keep on plane at slower speed, more efficient cruise performance, and less vibration were exactly what I was looking for.

 

[JoLin]

Re: 3 blade to 4 blade aluminum on 26' cruiser

I've been kicking that idea around for nearly a year. I think I'll take a shot this season on a pair of Solas Amita 4-blades to replace the OEM 3-blades that are on there now.

Jestor, did you decrease pitch, too?

 

[dingbat]

Re: 3 blade to 4 blade aluminum on 26' cruiser

For any one who might be interested. Midle of last sumer I replaced the three blade 19 pitch aluminum prop on our 26' aft cabin with a 454 magnum on an alpha drive, with a 17 pitch four blade aluminum.
The RPM at cruising dropped by 300. It gets up onto plane in 2/3 the time. Top speed went from 38 MPH to 44MPH.

You reduced the pitch by 2" yet gained 6 MPH? Makes no sense unless your old prop was toast.

 

[jestor68]

Re: 3 blade to 4 blade aluminum on 26' cruiser

I've been kicking that idea around for nearly a year. I think I'll take a shot this season on a pair of Solas Amita 4-blades to replace the OEM 3-blades that are on there now.

Jestor, did you decrease pitch, too?

Yes, I went from 18" to 17" on the 4 blade. It is recommended to reduce an inch of pitch in order to maintain rpm. If you stay with the same pitch, you might lose 100-200 rpm at WOT.

 

[jestor68]

Re: 3 blade to 4 blade aluminum on 26' cruiser

You reduced the pitch by 2" yet gained 6 MPH? Makes no sense unless your old prop was toast.

It may possibly be that the Solas prop is so much more efficient than some others that it is possible to gain some.

 

[JoLin]

Re: 3 blade to 4 blade aluminum on 26' cruiser

Yes, I went from 18" to 17" on the 4 blade. It is recommended to reduce an inch of pitch in order to maintain rpm. If you stay with the same pitch, you might lose 100-200 rpm at WOT.

Yeah if I could drop 1" I wouldn't hesitate, but I'd need to go from 17p to 15p because of what Solex has available for my engines and drives. If I were going from an aluminum 3-blade to stainless 4-blade, 2" would be fine (I did it several years ago on a 21' Pro-Line). Guess I'll keep 'waffling' awhile longer

 

[dingbat]

Re: 3 blade to 4 blade aluminum on 26' cruiser

Or it could be that the Solas prop is so much more efficient than some others that it is possible to gain some.

With the drop in pitch it would take an 24% increase in RPM or decrease in slip to obtain those speeds. I don't doubt the 4 blade performance in as much as the previous setup was junk.

I went from a 3 blade aluminum to a 4 blade stainless. Keep the same size prop, dropped rpm ~100 rpm, dropped top speed ~ 1.5 MPH

 

[jestor68]

Re: 3 blade to 4 blade aluminum on 26' cruiser

Yeah if I could drop 1" I wouldn't hesitate, but I'd need to go from 17p to 15p because of what Solex has available for my engines and drives. If I were going from an aluminum 3-blade to stainless 4-blade, 2" would be fine (I did it several years ago on a 21' Pro-Line). Guess I'll keep 'waffling' awhile longer

To clarify; I went from a 15.5 X 18 3 blade to a 14.5 X 17 4 blade. So I dropped an inch of diameter as well as an inch of pitch. I gained 100-150 rpm at WOT. Also, different brands; from a Mercury to a Solas.

 

[jestor68]

Re: 3 blade to 4 blade aluminum on 26' cruiser

For any one who might be interested. Midle of last sumer I replaced the three blade 19 pitch aluminum prop on our 26' aft cabin with a 454 magnum on an alpha drive, with a 17 pitch four blade aluminum.
The RPM at cruising dropped by 300. It gets up onto plane in 2/3 the time. Top speed went from 38 MPH to 44MPH. I don't have a read on the fuel consumption yet.
My suplier said he has had similer feed back from others. He also said that with 330 hp I should be using a stainles prop, but it's out of my price range.

I would be interested to know what rpm's you were/are turning with the different props.

 

[airshot]

Re: 3 blade to 4 blade aluminum on 26' cruiser

I have been thinking about switching to a 4 blade on my 22' Islander, all my research shows low end improvement but not much information on fuel consumption. Any ifo on fuel consumtion from someone that has switched to a 4 blade would be greatly appreciated.

Airshot

 

[Lyle29464]

Re: 3 blade to 4 blade aluminum on 26' cruiser

330 HP and a 4 blade on a alpha! I would really ease into it from now on.

 

[wrench 3]

Re: 3 blade to 4 blade aluminum on 26' cruiser

You reduced the pitch by 2" yet gained 6 MPH? Makes no sense unless your old prop was toast.

The old prop was a rebuilt the summer before last. My max RPM with the 19 pitch was just under 4,000. With the 17 pitch I can make 4,200 revs. The prop shop thought that the engine got more torque at the increased RPM.

 

[wrench 3]

Re: 3 blade to 4 blade aluminum on 26' cruiser

I would be interested to know what rpm's you were/are turning with the different props.

At 25MPH I was turning 3,100 revs. With the 4 blade I'm turning 2,800 at the same speed. My maximum RPM went from just under 4,000 to 4,200.

 

[wrench 3]

Re: 3 blade to 4 blade aluminum on 26' cruiser

330 HP and a 4 blade on a alpha! I would really ease into it from now on.

Yep! I run with my fingers crossed. The factory rep said it was a matter of when not if, but it's normaly only working hard when were going up onto plane and we tend to stay there for a long time.

 

[dingbat]

Re: 3 blade to 4 blade aluminum on 26' cruiser

The prop shop thought that the engine got more torque at the increased RPM.

Torque doesn't translate into speed. Your increase in speed was the result of going from 20+% slip to 2% with the new prop.

WOT on that motor is 4400-4800 RPM so you are still a bit over propped. Probably the result of a low reduction Alpha drive