Three Blade versus four blade propeller

[motion30]

Thinking changing my props to a little larger pitch. I can get a good deal on a set of three blade props. The current ones I have are four blade. You think there is the big difference between the three and four blade props at 1300 RPM and approximately 8 9 miles an hour?

 

[Greg QS]

1. the pitch is completely different from 4 to 3 blade props. A prop shop should be able to tell you the estimated pitch for the 3 blade prop .
2. 4 blade props run smoother.
3 4 blade props are an upgraded prop. You will be down grading.
4 . 4 blade prop cavate less.

 

[rslifkin]

1. the pitch is completely different from 4 to 3 blade props. A prop shop should be able to tell you the estimated pitch for the 3 blade prop .
2. 4 blade props run smoother.
3 4 blade props are an upgraded prop. You will be down grading.
4 . 4 blade prop cavate less.

4 blades aren't automatically better. If the boat doesn't need the extra blade area available with 4 blade designs (in other words prop diameter isn't limiting) then a 3 blade is likely to be slightly more efficient, although if it's a high blade area 3 blade design vs a 4 blade with higher aspect ratio blades that may not be the case. Comparisons like that are rare though, typically the 4 blade will have comparable blade aspect ratio and more blade area. The 4 blade will typically be smoother although this depends on the boat and isn't always significant. And cavitation goes along with blade area. Some applications are highly loaded and will benefit from more blade area while others don't and don't have cavitation problems to start with.

 

[SoWhat]

I have not noticed any significant difference between 3 blade and 4 blade on my 22" props. I went with 4 blade because they had what I wanted in stock. In theory, with equiv. pitch, 3 blade should be a bit faster, but in practice I am unable to detect a difference.

 

[SteveK]

The internet says....
If you need improved low-speed handling or frequently boat in rough water conditions, a 4-blade propeller may be the best choice. A 3-blade propeller may be the better option if you prioritize top-end speed and efficiency.

I have 4 blade and agree .