2011 Tahoe Q7i

[USS MINNOW]

Looking to change from a 3 blade to a 4. (Mercruiser 5.0 Alpha One) Any suggestions? Current 19 pitch 14.5 diameter. Not sure what to look for?

 

[alldodge]

Looking to change from a 3 blade to a 4. (Mercruiser 5.0 Alpha One) Any suggestions? Current 19 pitch 14.5 diameter. Not sure what to look for?

The straight swap is 17 pitch 4 blade. If your looking for certain types of performance increase or reduction we need to know:
WOT rpm
GPS speed at WOT
Drive ratio

 

[USS MINNOW]

The straight swap is 17 pitch 4 blade. If your looking for certain types of performance increase or reduction we need to know:
WOT rpm
GPS speed at WOT
Drive ratio

WOT RPM = approx 4800
GPS speed at WOT = approx 52
Drive ratio = not sure?

 

[alldodge]

Assuming you have a 1:5 drive, your slip is at 9.8 present, which isn't bad. A 4 blade may reduce the slip but I think you could loose some top end. Now if you get a custom 17x4-blade which has some cupping it could get you up to the same speed. The issue is you get more lift from a 4 blade but it also takes more HP to turn it.

As an example, if you can turn a 4 blade 19P at same 4800 rpm, reduce the slip to 6 percent, you can reach 54 mph.

Everything is a trade off and your not doing bad now. What are you wanting to improve, hole shot, top end?

 

[USS MINNOW]

Assuming you have a 1:5 drive, your slip is at 9.8 present, which isn't bad. A 4 blade may reduce the slip but I think you could loose some top end. Now if you get a custom 17x4-blade which has some cupping it could get you up to the same speed. The issue is you get more lift from a 4 blade but it also takes more HP to turn it.

As an example, if you can turn a 4 blade 19P at same 4800 rpm, reduce the slip to 6 percent, you can reach 54 mph.

Everything is a trade off and your not doing bad now. What are you wanting to improve, hole shot, top end?

Looking to improve hole shot and slow speed maneuvering.

 

[alldodge]

The 4 blade will give you more hole shot and low speed, but as before I do believe you will loose some top end, but could also over rev a tad at WOT.

To keep reverse maneuverability you don't want any cup. Cup works for forward but keeps the prop from biting in reverse

 

[USS MINNOW]

The 4 blade will give you more hole shot and low speed, but as before I do believe you will loose some top end, but could also over rev a tad at WOT.

To keep reverse maneuverability you don't want any cup. Cup works for forward but keeps the prop from biting in reverse

Thanks for the help.