2 blade vs. 3 blade...

[greatlakestate]

What are the differences in using a 2 blade prop vs. 3 blade?

I am running a x440 on my 31" 700 brushed deep vee, but have a x437 3 blade that has yet to be sharpened and balanced. Is this one worth a try or does the 3 blade lead to overloading problems? ----Rob

[bwells]

2 blade for speed and 3 blade for power. I asked the same question and was told 2 blade is faster in the straights but a 3 blade is faster in the corners. Not sure on overworking the motor though. I have so much cooling on my motor, I'm not worried about any temp issues. Wait for other replies as I'm interested also as we seem to have roughly the same boat and motor.

[kevinlew211]

you will get more acceleration with 3 blades same dia with 2 blades, the top speed will be almost the same, also 3 blades prop with load the motor and esc about 30% more, thats mean you can trade acceleration for top speed by using a bigger dia or more pitch prop up to 30% more than your 3 blades, its your choice, normally the motor will be fine, you should worry about your esc's temp more.
In another case, some of 3 blades like Abc props has smaller blade's area less than some 2 blades props, in this case you will see less acceleration and more top speed EVEN its a 3 blades prop.
The best way is try all the props you can get, use your eyes to choice the acceleration you like and GPS for the top speed you are looking for.

[DISAR]

That's true. I am a bit confused about the 30% though. Suppose I use a 40mm diameter prop. the 30% increase means 52mm??? That's too big.

[paulwilliams]

Three blade props are supposed to reduce prop torque effects, as there is always one blade in the water. I stress "supposed" here - I've never tried a mono with a 3-blader.

Paul

[kevinlew211]

Three blade props are supposed to reduce prop torque effects, as there is always one blade in the water. I stress "supposed" here - I've never tried a mono with a 3-blader.

Paul

Thats mean you was over prop your motor, but if your motor can handle that 3 blades prop then you will see more torque increase compare to same size and series prop but 2 blades.

[Fluid]

Three blade props are supposed to reduce prop torque effects, as there is always one blade in the water....

No, the reason they reduce torque and can improve cornering is because you can run a smaller diameter 3-blade prop and get the same loading and efficiency as a larger diameter 2-bladed prop. Smaller diameter means less "leverage" from the prop to torque the hull over. The difference is usually small but can be enough to get a certain hull to perform better.

You will get about the same load with a 3-bladed prop that is 80% of the diameter of a 2-bladed prop with similar pitch. This is a 'rule of thumb' and can certainly vary either way. Blade area has an effect on this too.

As for the "2-bladed props are for speed, 3-blades are for torque" comments - the fastest FE boats in the world run 3-bladed props.

.

[bwells]

It seems there is no consenses (sp) on 2 verses 3 blade props. It's easier to balance a 2 blade than a 3 blade and do the fastest FE boats do SAW or course?

[RCprince]

Speed Always Win in Straight A-Ways... Dragsters or NASCAR ...Courses are for endurance SAW's are for speed.

[paulwilliams]

No, the reason they reduce torque and can improve cornering is because you can run...

Jay,

Point taken about 3-bladers being smaller, and hence reduced torque.

However, I'm sure I read something somewhere about 3-blade props being "damped" by virtue of always having one blade in the water which maintains a more constant loading on the prop, thus reducing effective torque reaction. A 2-blade prop has a point on each revolution where it is effectively unloaded, so the torque reaction imparted to the hull is not constant. I'll hunt around and see if I can find a reference for this, I'm sure I'm not imagining it!

Paul

[Fluid]

I'm certain you are not imaginging it, I've discussed that topic with Tom at Octura before. It does tend to damp out some of the driveline "shock" and may be more efficient in some setups. Intuitively that could effect the torque reaction, but since you reduce prop diameter at the same time you go from 2 blades to 3 it would be difficult to quantify.


.

[paulwilliams]

difficult to quantify.

Says it all! Theory is one thing, but theory and the real world don't always agree.

Paul