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Not sure if this belongs here but...I need some input.
Tinkering on a 26 Advantage Cat, Merc 525sc.
Whats the purpose and difference between a three and four blade propeller???
What does each make the boat do???
Advantages -vs- disadvantages on both???
Thanks for the help :D
Here is what I know...and I am sure there will be others putting in better info than me..
Four blade I think give you a better hole shot..bottom end, and less vibration overall compared to a three blade...
The most important thing that you can do is test. Every boat will like something different. I personally like to have the most blade area with the largest diamiter in a raked shape. Now every combo will act different. Yes the 4 and 5 blade props look why cool, but that does not mean it is actually the best for your boat.
Here is the way I usuallly go or try to go with an impeller;
Good -19" of pitch x 16.75" dia
Bad - 28" of pitch x 13.5" dia
Over exagerated but that is the way I go, it seems to make the boat more eficiant for all-around use.
Now as for race set-ups, again testing, testing, testing !!!
You want the best slip numbers with the least amount of blades in the water (more blade surface area = more drag).
Depending on the size/weight of the boat, a four blade will usually have better bite, which means better handling (less slip out of the hole, less cavitation on slow, hard turns, etc.).
Of course, there are many other factors, such as blade design (chopper, cleaver, round ear, cupping, etc.) as well as pitch and diameter.