4 blade prop vs a 3 blade.

[San Anita]

Last season when I repowered my Striper I put a 4 blade on my outdrive and my fuel consumption increased. I did upsize engines 305 to a 350 cu in at the same time but did not expect less fuel economy. Is the 4 blade less efficient on fuel? Anyone ever did a prop swap and got before and after results?
Bill

[Okie]

The angle of the blade is the main thing. It will vary with the weight and sieze of the boat you have. A tug boat uses a big prop for power and not speed so which do you want? I believe a three blade prop is the best in most cases. And the angle of the blade can be varied depending on what you want speed or power. Or a compromise of little of both.

[Starfish]

As Okie stated, the pitch and other factors in prop design will affect how your boat runs as much or more than the number of blades. In general a three-blade will have a slightly higher top speed and a four or five-blade will have better handling, but those are generalities and you really need to match the specific prop type (pitch, rake, material, diameter) to the application.

I would expect the motor swap would have a much bigger effect on your fuel consumption than the prop, but you do need to make sure your new prop matches your new motor.

[fish_on]

Start with chapter 1 when you get through all the chapters you will almost be a prop expert.

http://www.mercurymarine.com/chapter_1_-_history__development

[Freakwater]

I could be high, but from what I've read I believe the most efficient prop is a one blade prop, but that is very unstable. The more blades you add, the more stable/smooth/less vibration, but the less efficient.

Freakwater

[San Anita]

Thanks for the info. The original 3 blade that was on the 305 engine was removed after the 350 was installed due to the boat having a very fast top end and the RPM would run way high if Id let it.
With the 4 blade My top speed is 34MPH loaded (4 fat guys and 35 bags of ice)at 4300 RPM. And of course this is also my top /most fuel comsumption.
So the pitch and size seems correct, I was just wondering if I shot myself in the foot going to a 4 blade.
Fish-on, I will read the info you have and see what it has to say about fuel comsumption.
Thank, ifishers
Bill

[YaHoeeFishOn]

When Clara owned the Sad Sack in Ilwalco , He swapped 3-4 blades and he said he lost fuel economy . I didn't see wheels to know how different shapped they were. I do think he lost 1" pitch for extra blade .

[San Anita]

Thanks, Ill give a properly sized 3 blade a try next season.
Bill