New Props

fryedaze · Sep 20, 2017

My old prop blades were very thin and could be flexed with your thumbs. I purchased new DQX four blade props from Michigan Wheel to replace my three blade props. I went from 25X27 three Dyna to 26X24 four blade DQX. The new props shook the boat on sea trials. They came with a computer run out sheet that indicated they were with in the tolerance MW sets. Had to re-haul boat and send them out to be tuned. I have attached the computer scans. The original MW scan and the Millers Island before and after scan.
Sharing to help the next guy out :blush:

Ski in NC · Sep 20, 2017

My prop guy wants to scan and tune all new props that come through his shop. He claims that after casting and machining, the material "creeps". I'm not sure about that, but I follow his advice.

Did that get rid of your shake? How do you like them?

I like the DQX. Half tempted to replace my old skool three blade with DQX as I have a fair amount of prop noise at higher speed.

fryedaze · Sep 20, 2017

Ski in NC said:
My prop guy wants to scan and tune all new props that come through his shop. He claims that after casting and machining, the material "creeps". I'm not sure about that, but I follow his advice.

Did that get rid of your shake? How do you like them?

I like the DQX. Half tempted to replace my old skool three blade with DQX as I have a fair amount of prop noise at higher speed.

The 4 blade is smoother than the 3 blade. For the last 7 years I have always felt a little vibration in the wheel above 1400 rpm. Now I feel nothing the whole way to WOT.

Nomad Willy · Sep 20, 2017

The 4 blade is about the same level of vibration as the 3 blade. However a typical 3 blade replacement for a 4 blade would have greater diameter. That would bring the tips of the blades closer to the hull and could cause considerable vibration.

If there's plenty of clearence there should be very little vibration difference between the 3 and 4 blade props. Probably un-noticable on most boats or by most people. Which one you use should be predicated on other variables like power applied, prop clearence, gear ratios ect. I changed props on Willy awhile ago and had plenty of clearence so I could easily have bought a new 4 blade. After looking into it I bought a 3 blade. The big advantage the 4 blade over the 3 is the ability to absorb and effectively apply power. This is however just my opinion.

fryedaze · Sep 20, 2017

Nomad Willy said:
The 4 blade is about the same level of vibration as the 3 blade. However a typical 3 blade replacement for a 4 blade would have greater diameter. That would bring the tips of the blades closer to the hull and could cause considerable vibration.

If there's plenty of clearence there should be very little vibration difference between the 3 and 4 blade props. Probably un-noticable on most boats or by most people. Which one you use should be predicated on other variables like power applied, prop clearence, gear ratios ect. I changed props on Willy awhile ago and had plenty of clearence so I could easily have bought a new 4 blade. After looking into it I bought a 3 blade. The big advantage the 4 blade over the 3 is the ability to absorb and effectively apply power. This is however just my opinion.

My understanding is that with the change to 4 blade from three you keep the diameter and drop the pitch 1 to 2 inches. I dropped my pitch 2 inches and the performance is identical throughout all rpm.

Nomad Willy · Sep 20, 2017

fryedaze,
That sounds about right.
Gotta balance hp, blade area, #of blades, pitch and rpm.
All the above needs to match your hull and weight.

FF · Sep 24, 2017

"the performance is identical throughout all rpm."

Is the fuel burn much higher?

fryedaze · Sep 24, 2017

FF said:
"the performance is identical throughout all rpm."

Is the fuel burn much higher?

Man I hope not. It will take me a few fill ups to figure out consumption. I do not have fuel flow gauges.

Art · Sep 24, 2017

I was taught:

Less blades makes prop more efficient regarding "screw-through" water.

Also taught, in trade off:

The more blades of a well tuned prop then the less chance for vibration

In addition:

If there were a way to correctly balance a one bladed prop that would be the most efficient.

So:

Three blade props offer best of both worlds regarding screw-through efficiency and reduced chance for vibration.

And:

I've always wondered, seeing as [evidently] less blades = most efficiency... why IB, direct drive pleasure cruisers don't employ two bladed props. I'm sure with today's technology two blade props can be tuned to the finest of tolerances.

Therefore:

Currently, I'm sticking with my twin three bladers. Good push and no vibration.

FF · Sep 24, 2017

Way back small aircraft could get a single blade prop.

For boats the hassle is enough blade area may require a larger diameter.

AS the tip clearance is a percentage of the blades diameter a deeper draft might be required.

In smaller sizes 3 blades do fine ,and once the diameter goes over 24-28 inches the price goes WAY up.

32x32 3 blade from Ahoy in LA , expensive but sweet!

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