A 3-blade prop is faster then a 2- blade ?

[Nevs]

Yes. The world speed record was set with a 3-blade.. Why not a 2-blade prop ?

https://www.youtube.com/watch?v=Fr7D9_V4UZs

1. in a rigger my guess is that 50-70 % of the prop stayes in the water at full speed. ? = lift.
2. in a mono my guess is that 40-70 % of the prop stayes out of the water af full speed = anti lift.

[Nevs]

Ups. (2) 60-70 %.

[Peter A]

I may see this rather simply, but with a surface drive prop less than half of it is in the water at speed.
You can be sure of one thing though, the world speed record prop was years in the learning and development and you will not be able to buy one of those!
BTW Nevs, guessing is just that (and pretty much pointless), learning and understanding is valuable reality, and yes, generally a three blade prop of the same pitch and diameter will be faster than a two blade on the same setup.

[Fluid]

Actually, the record prop used last year was the exact same one used over a decade ago to set the world record. Joerg used that prop because he designed it, he had it and he trusted it. The differences in the interveniening decade was rpm and to a minor degree hull design. Understand that only one blade is in the water at a time because only the tips contact the water, the hub is well above the water surface.


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[Speed3]

The 3 blade has an extra blade to help create push for each revolution. In my experience I find that to be the case too. 3 blade faster than 2 blade.

[Nevs]

Then a 4 blade should be faster then a 3 blade ? A 6 blade faster then a 4. But "at one point" I guess you will just be hitting air. Not water.

[T.S.Davis]

There is so much more to this than a simply 3 vs 2 as it's not in a vacuum. By that I mean that a motor can potentially turn a 2 blade at higher rpm than a 3 blade with the same power pushing it. Some of my setups simply will not turn a 3 blade that makes any sense on my boat. Something will bake. So is the 3 blade faster or just making melty stinky crap in my boat?

The setup has to be planned out for the truly outrageous speeds that the JAG team is achieving. They're motor choices are based on the prop they believe is correct for the boat and the amperage they know they are capable of sustaining. They're not wing'n it like us mere mortals. They never were.

[Moonie]

Unless I try out every kind of prop that can be made I can not know if I got the fastest prop for my app. Unless I’m talking about just the props I have at my hands. I will never know all the props out there also technology is ever changing. In my time setting up boats I noticed a three blade do create more thrust if it’s the same prop but just one more blade added. I use both and some boats do to weight and rpm can not turn a three blade with out creating too many amps on the motor.

[photohoward1]

Props are jus gears. Move forward a set distance per rotation. They do slip though. So a 3 blade slips less than a 2 blade. But S terry stayed sometimes that slip helps keel things cool. IMO for racing monos and cats I like 3 blades. Hydros 2 blades. It’s just me. Cats I can keep the blade hi and have less in the water. Monos to to a point just not as adjustable. Hydros a 3 blade crates more lift. I like to run loose to keep things cool so I go with a 2 blade. Hope this helps.


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[Nevs]

In the case of the world speed record. He might not have had a choise. 3,4 kg boat. 63900 rpm. And I think 400 m to get to 200 mph, (2018). The prop was a 2044-3. Had it been a 2044-2. Or even a 2047 he would probably have had to much slip to get anywhere near 200 mph. I never tryed a 2,0 pitch. But once tryed a 1948-2 and a 1848-3 in the same, (mono) boat. The difference was extreme. Much much more then I have experienced with lower pich, (1,4) props.

[Speed3]

I did some data logging with an octura x646 3 blade and found it to draw amps almost similar to an octura x450 which I also datalogged.

The rpm underload was slightly lower than the 450.

I datalogged an octura m545 and found it to draw almost 160% less amps than the x450. The rpm underload was about 107% higher than the x450.

Decided to take a chance and mod my x646 3 blade, I detunged it and did and tried my best to balance it. The result was amazing after data logging with the same motor and cell count I found it to draw amps around the same as the m545. The rpm went up too.

The prop is so amazing now I don't know if I can find another prop to outperform it. Because the 3 blade is more efficient the 2 blade, less slip underload.

Before modding the prop it give speed similar to the x450. After modding the speed increase abit.

Based on my experience data logging I expect that an x452 would draw more amps than an x450 and the same with an x455.

I was testing rpm underload as a percentage based on ampdraw. The point is those bigger props while may have more pitch because of the rpm lose they likely will not match the speed of this x646 3 blade that I detunged. And because this prop load the motor so much easier you can run higher cell counts.

In fact the amps I would draw on 6s with this prop is what I would draw on 4s with the x450.

So image what that means if cell for cell it faster than the x450. Image what you can do with it.

The motor that was used is a leopard 4092 1730kv and the boat used was a proboat impulse 31.

The reason I shared that is because I want you guys to be knowledgeable of the potential of the x646 3 blade. By detunging that prop and the other necessary work done. You can get the advantages that I mentioned above.

[Moonie]

646/3 tongue off in my testing has much less trust to push a big hull than a x450/3 tongue off.

[Speed3]

I would agree that the x450 3 blade has more thrust. I am sorry I didn't make myself clear enough but I am referring for the use on smaller hulls like up to 36 inches. A 450 3 blade will pull very big amps.

A x450 3 blade prop will pull twice as much amps as this prop I am referring too. Once enough of the tounge is off.

With this prop you can run much higher volt once the motor can safely handle the higher rpm, while you would have to settle for much lower rpm with the x450 3 blade.

[kfxguy]

I think the reason a 2 blade is more common and usually faster is because an electric motor prefers the higher rpm whereas a gas more turns lower rpm. But of course theres exceptions to every rule. In my experience ive testes 3 blade vs 2 blade back to back and a three blade was always slower. But thats not a hugely scientific test because i didnt take more time trying to dial in the three blade. I probably gave up too early because it was much easier and faster to use a 2 blade to attain the speeds i was looking for. Plus the three blade usually pulled more amps.

[MadProps]

Then a 4 blade should be faster then a 3 blade ? A 6 blade faster then a 4. But "at one point" I guess you will just be hitting air. Not water.

No, at some point you have too many blades in the water causing resistance and you start impeding performance