3 or 4 Blade Prop?

[steffen300]

What is the difference between 3 and 4 blade Prop?
When diameter and pitch is the same?
Best wishes from Germany
Steffen

 

[papasage]

Re: 3 or 4 Blade Prop?

4 blade is for pulling a heavy load . 3 and 2 blade gives more speed . you match the blade with the boat and motor to keep the RPM`s at engin spec. or you could over rev @ WOT.
post the motor hp and the boat . the some one can tell you what to use .
my pontoon has a 4 blade aluninum prop .not sure of the pitch . i put a 3 blade 16 p on it and it ran real slow . a dealer said the setup i had it was gitting to much bite to turn the RPM`Sup for a 3 blade the book calle for a 11p.most outbords for sped you need a 13 p. jusr be sure your RPM`S are right . even under the mfg . spec isen`t good on a 2 stroke engin . they are built a dezined to run WOT .most of thetime

 

[Silvertip]

Re: 3 or 4 Blade Prop?

Theoretically there would be no difference in top end speed if pitch and diameter were the same on a 3 and 4 blade prop. However, Four blades adds some drag so in some cases loss of top end (not a great deal) is the trade off over a three blade. On the other hand, a four blade has an advantage during hole shot because of the extra blade. Four blades exhibit smoother operation. Remember though, you cannot compare a three blade of "X" pitch from manufacturer "A" and a four blade of the same pitch from manufacturer "B" and expect exactly the same result. There are other design factors that enter the equation so blade shape, rake, cupping, venting, and material (aluminum or stainless) all have an effect on performance. One prop may work well on one hull and not worth a hoot on another. Testing is the only real way to determine what characteristics you want for your boat. In a nutshell, prop selection is compromise between hole shot and top end. You give up one for the other.