20p 4 blade or 23p 3 blade

[Wessmith]

I have a force 150 that runs my 18ft cobra 47mph at 5400rpms, which is the peak of my recommended rpm range. I am adding boyesen power reeds which will add 100-300 rpms. Should I upgrade to a 23p prop? I heard the 20p 4 blade is equivalent to a 22p 3 blade. I pull alot of skiers, wakeboarders, and tubers. Which prop will do what and which is the better choice for me?

 

[walleyehed]

Re: 20p 4 blade or 23p 3 blade

I would stay with the prop you have now....I've installed reeds in 7 different engines, and have yet to see 100 RPM increase on any of them.<br />Idle and mid-range punch is where you will see the difference.

 

[Matthew A.]

Re: 20p 4 blade or 23p 3 blade

You'll lose a considerable amount of top end speed running a four bladed prop. Possibly 5 mph or more. More blades means more drag, more drag means less rpms. A good prop in rough seas as the extra blade gives it extra bite. Extra bite means less slippage and resistance to being ventilated by bubbles or debris. <br />They also make a good "hole shot" prop due to the extra bite. Tend to also get the boat up on plane quicker. <br />However, not a very good "all around" prop. compared to most 3 bladed props. Also, even though 4 bladed props are good off the line, the added drag of the additional blade can slow how quickly the motor gains rpm. What good is bite off the line if the motor isn't able to utilize it smoothly across the entire rpm range.

 

[Dhadley]

Re: 20p 4 blade or 23p 3 blade

Actually with todays 4 blade props its not unusual to find they are faster than a 3 blade beacuse of their ability to run a much higher X dimension.

 

[imported_bjs]

Re: 20p 4 blade or 23p 3 blade

ive heard that four blades make your boat ride rough ture or not.

 

[walleyehed]

Re: 20p 4 blade or 23p 3 blade

Brad, 4-bld is "usually" smoother due to balance issues.

 

[mmainelli]

Re: 20p 4 blade or 23p 3 blade

yes, more blades means more drag, but only because they're pushing more water than fewer blades. But the wheel is not passive. It's connected to an engine that's supposed to have the hp to fight and overcome the drag. And I agree that top end loss is yesterday's story. Today's blade designs are vastly improved. In fact, some Alum props are almost efficient as SS. Bring on the hp, don't fault the prop. Recall WWII P-51s, where Northrup put a 4 blade prop on a Cummins straight 8, for faster climb and top end. But they put the horses behind it.

 

[walleyehed]

Re: 20p 4 blade or 23p 3 blade

That would be cool if we could just "up" the HP to suit the prop...But, as with many boating issues, we have to maximize the set-up as is and move fwd from there. The end result, if we do it right, will be a higher pitch prop with the same HP, at the same or higher RPM..<br />BTW, the 4-blade on the -51 was to shorten blade length for efficiency, yet harness the available HP....also quieter.