4 Blade vs. 3 Blade

[Belchy]

I am going to start using my 9.9 Mariner as a kicker to a 25 ft. W/A. The question I was wondering about is, how much of a difference will it make using a four blade prop vs. a three blade (currently the one I have on it.) Idealy I would like to test the both out, but was just looking for opinions from everyone right now.<br /><br />Thanks in advance for the advice<br /><br />Belchy

 

[ziemann]

Re: 4 Blade vs. 3 Blade

There are many questions that should be asked here....but the first.....why do you think you need a new prop and what are you hoping to achieve?

 

[Navigator]

Re: 4 Blade vs. 3 Blade

Belchy,<br /><br />Going from 3 or 4 blades on a 9.9 isn't going to increase anything except the boating ramp "cool factor", plus its going to rob more power since it has to push 4 blades through the water.<br /><br />Get a 3 blade prop that lets the rig run comfortably in the correct RPM range and your engine will last a long long time.<br /><br />Nav

 

[DJ]

Re: 4 Blade vs. 3 Blade

The REAL issue here is not the number of prop blades. It's PITCH.<br /><br />Typically, the four blade props are made for heavy loads. However, a four blade prop, of the wrong pitch, will ruin your engine.<br /><br />Regardless of blade count, prop the engine to be able to achieve its wide open throttle RPM rating, with the desired load.<br /><br />Otherwise, you're guessing with potentially disastrous results.

 

[Belchy]

Re: 4 Blade vs. 3 Blade

Perfect, that is what i needed to hear... think i will stay with the three blade..thanks fellas <br /><br />Belchy

 

[ziemann]

Re: 4 Blade vs. 3 Blade

Exactly guys!<br /><br />For some reason, some folks think that "if 3 blades are good, 4 blades must be better!"<br /><br />As stated, the whole goal is to reach peak RPM.

 

[mjbrueck]

Re: 4 Blade vs. 3 Blade

I think you were on the right path, but were asking the wrong question. Unless you already have a "trolling" prop on the motor, you should get one. For a 9.9hp on a 25' boat, you should probably be using a prop with a 5" or 6" pitch (it could be 3 or 4 blade). A typical stock prop with a 9" or 10" pitch will only let you turn around 3000 rpms, which will quickly kill that motor.

 

[KCLOST]

Re: 4 Blade vs. 3 Blade

In my experience, the four blade props are slightly less in diameter to lessen the extra forces needed to turn it... I see only a slight difference in rpm between a 24P trophy and lets say a Lazer II of the same pitch. The trophy is 13-3/4" and the Lazer is 14-1/2".<br />For a small engine such as yours I'm not sure what size difference, if any there will be...