3 blade vs 4 blade

[craig mac]

the august motor boating magazine has a brief article on a 28 bertram that was repowered with 260 hp yanmars--they did some tests with 19 x21 3 blades, 19 x 20 4 blades, and 20 x19 4 blades

3 blades performed best at WOT and gave up a little in the mid range---they claim the 4 blades were smoother--confirming what I have been reading all along.

[Kingfish]

Did they say anything about fuel economy with the different Blades?

I've been thinking of going to the 4 blade myself.

[mike ohlstein]

More surface area means more drag. I believe that three blade props are more efficient.

Four blades are smoother, but fine balancing might correct a three blade prop.

I find that I get a better wake pattern and nicer clear water area behind the boat with four blade props.....and catch more fish with them.

[Sean B]

Now I just can't let that one go by.....you say you catch more fish by turning more prop blades?

[mike ohlstein]

Yes, and they hit closer to the boat.

[thereheis]

if thats the caseand what it takes to catch more fish , then i am gonna have a set of 6 blades made

:lol: phil

[craig mac]

there was no mention of fuel consumption---there was a table of RPM and MPH

[JP Dalik]

The 4 blade prop will typically run a more efficient cruise then 3 blade. The standard rule of thumb is if you run a 20x25 3 blade, remove an inch of pitch and that's the 4 blade number in this case it would be 20x24.
You should expect to pick up .5 to sometime 2.0 kts at cruise by switching to 4 blade wheels (depending on manufacturer). Keep in mind that your top end speeds will flatten out, but where it counts is at cruise and thats where the pay back is.
Michigan and S&S have done some great jobs for the folks running B31's up here.

[dougl33]

This is not the first time I've heard the comment about picking up more speed at cruise with the 4 bladers. I switched from 3 bladed Michigan Nibrals (20x18 with a light cup) to 4 bladed Michigan Nibral DQX (20x16 with a light cup). Top RPMs stayed about the same at 4100rpms, but my cruise RPM's increased by about 100 rpms to acheive the same 18-19 knot cruise. The 4 bladers are nice and smooth though.

Also, in the article mentioned above, the best cruise speed was attained with the 3 bladers, seeming to back up what I discovered on my boat.