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.


.

[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.


Sent from my iPhone using Tapatalk

[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

[grsboats]

Lots of records were set using 2 blade props .Here my practical example: my 6S rigger turning an Octura V947/3 made hundreds of passes from 105-108 mphs Weeks ago turning an ABC 1820-22-45%(2 blade) top speed was 109,4mph with same set up. Basically they have the same diameter but different picth.The V947/3 has 3,5 pitch and the ABC 3,6. My nitro and Gas riggers are faster turning two blade props,so you have to seriously consider the final pitch to be faster and not necessarily the number of blades.
Gill

[rol243]

yes the 3 bladed props are great if your oval racing mono hulls etc as the blades do help in coming out of turns, the 2 blade props do seem to be more favoured especially with riggers.

[Speed3]

The fastest rc boat record in the world had on a 3 blade prop, do you guys think he would have been faster with a 2 blade?

[rol243]

I would say just about all other records have been set with the use of correct and modified 2 bladed props. that world record holder for fe rigger certainly would have been using some fancy designed 3 blade prop for sure, not your average run of the mill job.

[Speed3]

I detunged a x646 3 blade. And its the fastest prop I have test. It is significantly faster than an octura m447, m645, m545, x642, x450. Grimracer 4255, ABC 1814 17 45 2 blade. And graupner k42.

It used to pull amps almost similar to the x450. And loaded rpm was similar to the x450 and speed was around the same before I detunged it.

After I detunged it I gained 1.5mph.

I know that sound much.

But to get an understanding of what my boat did with it. On 3s with a leopard 4092 2080kv my boat was faster than most of the out of the box boats using 6s in stock form. I did not say all but most. And the fastest of them my boat would have been close too. And that's while those boats using 6s and I mine using 3s.

On 4s the boat was way to aggressive. I have to slowly accelerate to max speed, it flips almost instantly if I give full throttle from a dead stop or the boat moving slow.

The boat is a revolt 30.

[Speed3]

I took 2 millimeters off of the tounge on each blade for my x646 3blade then file off some metal on each blade so that the heaviest part of the prop was in the center.

Basically the blades would look almost similar to the m645 in shape.

I did not reduce the diameter of the prop.

This reduced the ampdraw by a factor of 1.4 causing the rpm to increase and the speed also increased.

The beauty about this prop is because it loads like an m545 you can use it on motors that you would have used the m545 on and get befits in terms of speed as props over 50mm.

And cases where you want to run higher rpm setups you can try this prop.

[grsboats]

Definitevely the JAG team is in another league as everything is a consequence of years of testing and devotion and no combustion rigger can be compared to a Fe one.I don't know if they have tried a two blade props but I'm pretty sure if so lot of details would be take into consideration to get this huge sucess.
Gill

[Nevs]

In the video(16) he only holds full trottle for about 1,2-1,4 sek. He uses a 2044-3. Meaning it turns 88mm through the water pr. rotation. Each blade has to cover 29,33 mm of that distance. With a 2044-2 each blade would have to cover 44 mm..So you would need more pitct pr. blade. More pitch is less acc. I think, and Combined with less propeller area in the water I think the 400m was an important factor in the decission to use a 3-blade...My guess.

[Speed3]

A 3 blade prop does have blades the same dimensions as the 2 blade prop rated to have the same pitch.

Example a x450 2 blade each blade has 36mm of pitch.

Strangely the x450 3 blade each blade would have 36mm of pitch.

Now if the 3 blade have each blade at 36mm of pitch and the 2 blade have each blade at 36mm of pitch which have more pitch? In my thinking was wondering does the 3 blade have 1.5 times more pitch than the 2 blade really? And why is it rated to have the same pitch if it has an extra blade the same dimensions as the 2 blade?

What I found interesting is the fact that a x646 3 blade pulled amps almost similar to a x450 2 blade.

Same cell count and motor.

And I was shocked when I saw the datalogged of the x646 3 blade that I detunged it was pulling amps similar to an m545 after detounging.

[Speed3]

Interestingly not all prop makers measure the prop pitch the same.

I have a prop for a gases engine which is said to be 6717.

67 mm diameter and 1.7 pitch ratio. The blades are much smaller than other props for the gas boat. Actually each blade has about 38mm pitch so if you multiply 38 * 3 that will total 114mm then divide 114mm by 67mm diameter and you get 1.7 pitch ratio.

The octura is different though if I use the same method to measure the x646 3 blade. Each blade at 34mm pitch, I would get 34 * 3 = 102mm divide that by 46 (102/46= 2.217)

The octura x646 3 blade would have a 2.217 pitch ratio.

The point is not all prop makers calculate the pitch the same for a 3 blade.

So I don't know if this mean anything.

[Nevs]

Could it be because the octura x646 was designed with a toung that is overlapped by "the previous" blade when running not detouged. it should be 46x1,6 =73,6 mm :3 = 24,53 mm pr blade. Or about 10 mm overlab before detounging ?

[Speed3]

The blades are in such a position that as soon as one blade is finish the other starts immediately.

I would have though the 3 blades would add up to around 72 to 74mm of pitch. But it is 34mm per blade.

[blackout]

A 3 blade prop does have blades the same dimensions as the 2 blade prop rated to have the same pitch.

Example a x450 2 blade each blade has 36mm of pitch.

Strangely the x450 3 blade each blade would have 36mm of pitch.

Now if the 3 blade have each blade at 36mm of pitch and the 2 blade have each blade at 36mm of pitch which have more pitch? In my thinking was wondering does the 3 blade have 1.5 times more pitch than the 2 blade really? And why is it rated to have the same pitch if it has an extra blade the same dimensions as the 2 blade?

What I found interesting is the fact that a x646 3 blade pulled amps almost similar to a x450 2 blade.

Same cell count and motor.

And I was shocked when I saw the datalogged of the x646 3 blade that I detunged it was pulling amps similar to an m545 after detounging.

The X450/2 and X450/3 have the same total pitch, 70mm. One revolution will move the boat forward 70mm assuming zero slip. In theory, the 3-blade will have less slip because there is one more blade helping to do the work of moving the boat forward that 70mm.

[RaceMechaniX]

Surface piercing propeller theory is one of the best sciences that cannot be simply explained with calculations and numbers. It's 90% tribal knowledge followed by cut and try techniques. The best guys in the world have bent, cut, detoungued, shaped, profiled, cupped to the "n"th degree to learn what they know and hopefully share with the rest of us a fraction of it. Joerg, Arne and Gunnar spent years perfecting a blade shape that works with their set-up. That same prop on a different boat has very different results. Team JAG went from 140MPH to 200MPH not because of the prop, but because of the power system. They probably had triple the power today compared to the round cell days.

Consider this: All the nitro and gas SAW Hydro records I am aware of were set with 2 blade props. Brian Buaas ran 139mph in a P-hydro with a 2-blade ABC prop.

Just to say there is no correct answer.

[rearwheelin]

On my mono it seems like the 2 blade gets the boat out of the hole much faster but the 3 blade has a higher speed. 4402b vs. 4403b...