Any one running Sharrow Props?
04-14-2024 | 06:48 AM
#11
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From: SW Ohio
A propeller with one blade has the best efficiency, but unfortunately it is practically impractical.
The best propeller is the one that accelerates the water mass with the least parasitic resistance, that is, with the least disturbances in the flow. Some curves, which first bend the flow in one direction, then redirect it in another direction, are the exact opposite of this.
Is there any explicit explanation why this propeller is better than the classic ones? What I have read so far is all in the style of "National Geographic", which explains for an hour and says nothing.
I did not find anywhere, for example such datas:
- classic propellers can handle such a dynamic pressure in a certain regime, and our propeller can handle such a dynamic pressure.
- the best comparable classic propellers have such parasitic resistance, and ours has such.
- the best comparable classic propellers have such a slip on a sample vessel, and ours has such a slip.
- the best comparable classic propellers have such an efficiency on a sample vessel, and ours has such an efficiency.
- At some mechanical engineering universities, a diploma thesis sometimes appears with the title: "Calculation of the ship's propulsion", and at the end of it, a huge amount of data is covered in the form of diagrams. Could this be seen for this propeller?
For example why I miss reall datas:
"The special shape of the blade reduces noise, which reciprocally increases efficiency."
Has anyone considered how much db(A) means 500W of losses, if all of this goes into noise? Sound sometimes has no noteworthy connection to efficiency at all.
The best propeller is the one that accelerates the water mass with the least parasitic resistance, that is, with the least disturbances in the flow. Some curves, which first bend the flow in one direction, then redirect it in another direction, are the exact opposite of this.
Is there any explicit explanation why this propeller is better than the classic ones? What I have read so far is all in the style of "National Geographic", which explains for an hour and says nothing.
I did not find anywhere, for example such datas:
- classic propellers can handle such a dynamic pressure in a certain regime, and our propeller can handle such a dynamic pressure.
- the best comparable classic propellers have such parasitic resistance, and ours has such.
- the best comparable classic propellers have such a slip on a sample vessel, and ours has such a slip.
- the best comparable classic propellers have such an efficiency on a sample vessel, and ours has such an efficiency.
- At some mechanical engineering universities, a diploma thesis sometimes appears with the title: "Calculation of the ship's propulsion", and at the end of it, a huge amount of data is covered in the form of diagrams. Could this be seen for this propeller?
For example why I miss reall datas:
"The special shape of the blade reduces noise, which reciprocally increases efficiency."
Has anyone considered how much db(A) means 500W of losses, if all of this goes into noise? Sound sometimes has no noteworthy connection to efficiency at all.
"Noise" is being used in a physics reference here, and sound is a product of noise, not an interchangeable term. We hear sound coming from a bad wheel bearing because noise is being induced into the frame of the car, but it's the noise that furthers the damage; the sound just annoys us. We see noise in our prop wash as turbulence or froth behind the prop, but couldn't hear it, even without the engine drowning it out. In the simplest explanation, energy spent creating noise is energy NOT spent creating thrust.
All that said....
It is a fact that Sharrow has not released any real data, and all their "testimony" has been from paid "testers", or vested parties. They are relying on consumers' curiosity to sell what could ultimately turn out to be snake oil. I do believe they are of some benefit to those seeking efficiency over performance, as the physics is sound and proven elsewhere: Toroidal propped drones' batteries last longer, for example. The proof will be in whether the ROI will be within a useful timeframe for those who buy them. Who knows....
I also believe there could be some benefit from the technology in the performance market if they were to invest in deigns that make for stronger props, which I believe is the Achilles heel in making them practical for us powerboaters. But they're not, so...
So far, I'm just fascinated in the videos showing them being machined. I might be geeking out from professional fanboi-ism, but 5-axis machining is just cool. Just sayin'....
Thanks. Brad.
04-14-2024 | 01:43 PM
#12
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I wouldn't mix drones with marine propulsion. The drone's propeller spins in air, which is about 950 times lighter than water.
Example:
- an airplane propeller with 20% slip has almost 80% efficiency!
- a nautical propeller with 20% slip has 40-60% efficiency.
The air is thin enough that the main losses are in slip and induced drag. The main part of the resistance of a marine propeller is the simple frictional resistance, there is very little induced resistance and the Sharrow design reduces the induced resistance (unnecessary work in water) and increases the frictional resistance of the working surface of the blade and blade lop.
I play with marine propellers as a hobby, but I make a buisenes from bigg props for moving air and I roughly understand what it is all about. I'm not very smart, but I wouldn't put such a shape on the shaft of my drive, if the manufacturer don't explain very well what, how and why, and even then I'd test it first to see if there really is something on it. I'm really having trouble understanding why this propeller would be better than the classic. The USA has first class submarines that are fast and quiet. But why don't they use this innovation there? And don't tell me they don't know it
Example:
- an airplane propeller with 20% slip has almost 80% efficiency!
- a nautical propeller with 20% slip has 40-60% efficiency.
The air is thin enough that the main losses are in slip and induced drag. The main part of the resistance of a marine propeller is the simple frictional resistance, there is very little induced resistance and the Sharrow design reduces the induced resistance (unnecessary work in water) and increases the frictional resistance of the working surface of the blade and blade lop.
I play with marine propellers as a hobby, but I make a buisenes from bigg props for moving air and I roughly understand what it is all about. I'm not very smart, but I wouldn't put such a shape on the shaft of my drive, if the manufacturer don't explain very well what, how and why, and even then I'd test it first to see if there really is something on it. I'm really having trouble understanding why this propeller would be better than the classic. The USA has first class submarines that are fast and quiet. But why don't they use this innovation there? And don't tell me they don't know it
04-14-2024 | 02:21 PM
#13
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Joined: Jun 2021
Posts: 3,533
Likes: 2,137
From: SW Ohio
I wouldn't mix drones with marine propulsion. The drone's propeller spins in air, which is about 950 times lighter than water.
Example:
- an airplane propeller with 20% slip has almost 80% efficiency!
- a nautical propeller with 20% slip has 40-60% efficiency.
The air is thin enough that the main losses are in slip and induced drag. The main part of the resistance of a marine propeller is the simple frictional resistance, there is very little induced resistance and the Sharrow design reduces the induced resistance (unnecessary work in water) and increases the frictional resistance of the working surface of the blade and blade lop.
I play with marine propellers as a hobby, but I make a buisenes from bigg props for moving air and I roughly understand what it is all about. I'm not very smart, but I wouldn't put such a shape on the shaft of my drive, if the manufacturer don't explain very well what, how and why, and even then I'd test it first to see if there really is something on it. I'm really having trouble understanding why this propeller would be better than the classic. The USA has first class submarines that are fast and quiet. But why don't they use this innovation there? And don't tell me they don't know it
Example:
- an airplane propeller with 20% slip has almost 80% efficiency!
- a nautical propeller with 20% slip has 40-60% efficiency.
The air is thin enough that the main losses are in slip and induced drag. The main part of the resistance of a marine propeller is the simple frictional resistance, there is very little induced resistance and the Sharrow design reduces the induced resistance (unnecessary work in water) and increases the frictional resistance of the working surface of the blade and blade lop.
I play with marine propellers as a hobby, but I make a buisenes from bigg props for moving air and I roughly understand what it is all about. I'm not very smart, but I wouldn't put such a shape on the shaft of my drive, if the manufacturer don't explain very well what, how and why, and even then I'd test it first to see if there really is something on it. I'm really having trouble understanding why this propeller would be better than the classic. The USA has first class submarines that are fast and quiet. But why don't they use this innovation there? And don't tell me they don't know it
I’d bet the relative density would increase the effect of reduced loss, not reduce it.
The fact that our submarines don’t employ this prop technology might be as simple as that they have not decided to investigate it yet. It wouldn’t be the first time, by a lot, that a private sector development was adopted for military use. These props have not been on the market for very long. It was several years between the inception of the LIM drive for roller coasters was developed for aircraft carriers. The military can be quite stubborn sometimes.
I agree the jury is still out, and it’s very possible the reason Sharrow is not sharing any test data is that it’s not as good as it might appear. But I’m betting on the physics.
Thanks. Brad.
04-16-2024 | 06:22 AM
#14
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Airplanes have better efficiency at higher altitudes because the fluid is thinner.
In the case of an aircraft propeller, the main losses are in the slip. there is still some induced resistance, friction is negligible.
A propeller in water often has a better efficiency if you increase its slip. This means that there is less blade surface in the water, and in water you can almost forget about the induced resistance due to the inertia of the water. The main problem here is the resistance to movement through the water.
This prop would be comparable to a classic propeller up to a certain dynamic pressure, but when the dynamic pressure increases enough that the negative pressure currents of the inner part of the "knot" meet the pressure currents of the rear-outside part of this knot, the joke is over, because an effect similar to that by biplanes is created.
04-16-2024 | 07:48 AM
#15
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Joined: Jun 2021
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Likes: 2,137
From: SW Ohio
Wrong.
Airplanes have better efficiency at higher altitudes because the fluid is thinner.
In the case of an aircraft propeller, the main losses are in the slip. there is still some induced resistance, friction is negligible.
A propeller in water often has a better efficiency if you increase its slip. This means that there is less blade surface in the water, and in water you can almost forget about the induced resistance due to the inertia of the water. The main problem here is the resistance to movement through the water.
This prop would be comparable to a classic propeller up to a certain dynamic pressure, but when the dynamic pressure increases enough that the negative pressure currents of the inner part of the "knot" meet the pressure currents of the rear-outside part of this knot, the joke is over, because an effect similar to that by biplanes is created.
Airplanes have better efficiency at higher altitudes because the fluid is thinner.
In the case of an aircraft propeller, the main losses are in the slip. there is still some induced resistance, friction is negligible.
A propeller in water often has a better efficiency if you increase its slip. This means that there is less blade surface in the water, and in water you can almost forget about the induced resistance due to the inertia of the water. The main problem here is the resistance to movement through the water.
This prop would be comparable to a classic propeller up to a certain dynamic pressure, but when the dynamic pressure increases enough that the negative pressure currents of the inner part of the "knot" meet the pressure currents of the rear-outside part of this knot, the joke is over, because an effect similar to that by biplanes is created.
There is no comparison to biplanes. The blades are not stacked. They are in line with each other until they begin to transition into the "knot". The "knot" is redirecting water as thrust, making use of the energy, rather than water being cast off radially, wasting the energy. That water is not being exerted against any other part of the prop at all. At no point are the two sections of the blade competing with each other or one of them counteracting the lift of the other. Where it might appear the leading blade would be forcing water onto the trailing blade, the trailing blade is at a higher pitch, acting like cup, as it transitions into the loop. The two sections and the loop all work together. And the reference to toroidal drone props explains why.
Part of the problem here is the utter lack of pics of these props that really show how the blades are arranged. This is obviously an effort to protect their IP. I'd REALLY like to see these props on a simulation modeling software, but that ain't gonna happen.
I also just noticed they have developed a duo-prop set. Don't know if this is recent news or if they've had it for a while. It's been since they originally publicized the concept that I've been on their website. It's kind of interesting how the forward prop is essentially a six blade, with a loop between each of the three pairs of blades, while the rearward prop is more like their original prop. Makes for a much shorter hub on the forward prop. Makes you wonder why they didn't make them both like that for the duo-prop set.
Thanks. Brad.
04-16-2024 | 08:26 AM
#16
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Anyway, I don't want to go deeper into this debate, it's not my problem. Sorry that I start it.
However, I am sure that it is difficult to find a serious hydrodynamicist who would confirm the advantages of such a design. This is not a technical, but a design-commercial construction.
As I already wrote, water is heavy enough that due to inertia there are no problems with induced resistance. The Cleaver is the most efficient form of propeller for high dynamic pressures. The blade does not lift transom due to the centrifuge and it doesn't have any hydrodynamic shapes to prevent radial water movement because it doesn't need it.
If this prop really effectively changed the direction of water movement due to the lop it would be on the first blade. The seccond blade is curved further forward and this blade is even more sensitive to radial water movement than the classic prop. (What makes the first wing better makes the second worse, if there really was anything to it.) A few drawn vectors quickly explain the problem. And the comparison with the biplane is very good. It was in your country that a buissenes jet plane with a comparable wing shape was researched years ago, but as it was already known, it did not work. However, many subsidies went to research...
bye and good luck indeed
However, I am sure that it is difficult to find a serious hydrodynamicist who would confirm the advantages of such a design. This is not a technical, but a design-commercial construction.
As I already wrote, water is heavy enough that due to inertia there are no problems with induced resistance. The Cleaver is the most efficient form of propeller for high dynamic pressures. The blade does not lift transom due to the centrifuge and it doesn't have any hydrodynamic shapes to prevent radial water movement because it doesn't need it.
If this prop really effectively changed the direction of water movement due to the lop it would be on the first blade. The seccond blade is curved further forward and this blade is even more sensitive to radial water movement than the classic prop. (What makes the first wing better makes the second worse, if there really was anything to it.) A few drawn vectors quickly explain the problem. And the comparison with the biplane is very good. It was in your country that a buissenes jet plane with a comparable wing shape was researched years ago, but as it was already known, it did not work. However, many subsidies went to research...
bye and good luck indeed
Last edited by plavutka; 04-16-2024 at 08:30 AM.
