Interested to know what you guys think about Counter Rotating Propeller CRP ?
Advantages:
• Counteracting the propeller torque.
• Small increase in efficiency (Some claim 10%)
• Higher speed for smaller diameter
• ?
Disadvantages:
• Adds complexity
• Adds weight
• ?
Quick Concept needs work.
Over to you guys.
Cheers,
Al
Excuse my bad English. I use google translater.
This system is not bad. I also thought about installing this in my jet pump. The advantage is not only to counteract the torque. A propeller creates a spin behind the propeller in the water. This is an unused energy for locomotion. With the second propeller you also try to use this energy and take the spin out of the water. With a jet pump, this is done with flow baffles in the nozzle. This is easier on the construction. This two-propeller system is commonly used on exposed propellers. In e-foils and jet boards, however, the propellers are in one nozzle. I think that the Auwand is not worth it. But I can be wrong too. You just have to give it a try. I’m looking forward to your results.
I think that’s great if you try that.
i think at the beginning this was designed so that it won’t spin on itseft mainly and/or to keep in straight line to the target?
increased in efficiency ? energy wise?
Yes, that’s right. The drawing that theone has set here comes from a torpedo. And a straight ride is very important. Volvo Penda has further developed this drive for pleasure boats. And there the performance is increased. Here is a link to it. https://de.wikipedia.org/wiki/Duoprop
All,
The concept is still very much a work in progress.
Is anyone any good at propeller design ? & interested in counter rotating systems ?
Cheers,
Alex
Counter Rotating Propeller are only suitable for torpedo drive. They are not suitable for e-foil drive because such a drive has very low efficiency. To propel e-foil, one propeller is enough, but it must be well designed to have the highest efficiency.
@WNT thanks for the input , can you please explain your reason for claiming “low efficiency” ?
What do you consider the most efficient single efoil propeller setup in the public domain ? (I would like to use the best available as a bench mark )
What are you currently ruining ?
Do you think the guys at Volvo duoprop were telling lies ? https://www.volvopenta.com/marineleisure/en-en/products/info/for-motor-yachts/volvo-penta-ips.html
Many thanks,
Alex
@Hiorth All your videos are inspiring . I will share my progress as well.
I have been designing around the gears in this photo.
Thanks .
Alex
The first propeller (green) needs a laminar flow at the inlet. At the exit, however, it produces very strong turbulent flow (bubbles, cavitation, waves, etc.).
The second propeller (red) also needs a laminar flow at the inlet. However, as the laminar flow does not come to the second propeller, the efficiency of the second propeller is very low. This consequently causes low efficiency of both propellers together.
The hydrodynamic properties of the propellers (the input requires laminar flow, the output always generates turbulent flow) can not be changed, so it applies to Volvo Penta IPS, Rolls Royce and so on.
I wonder, does something like CR impeller exist? I heard about some radial water pumps using it but i am not sure how it works. Any axial double impeller setup throughout the history?
So, should we have a pull configuration instead of a push?
@WNT Thank you ! great explanation, perhaps the Volvo system advantage comes from forward facing propeller without any turbulent flow ?
again what do you consider the best available propeller pitch for a efoil ?
@Just please see link above the Volvo clain is:
Thousands of applications with the distinctive, forward-facing, twin counter-rotating propellers and individually steerable pods have been installed in hundreds of boat models worldwide. A few of the many benefits when comparing to inboard shafts are:
40% longer cruising range
20% higher top speed
30% reduced fuel consumption
30% less CO2 emissions
50% lower perceived noise
More onboard space
Cheers,
Alex
I did see. I am talking about impeller not propeller. I cant seem to see counter rotating jet drive on Volvo web. I did hear about double impeller radial water pump but i cant remember where or in what aplication. Could double impeller increase pressure ratio in comparison to a single impeller? Was there some working design in history or nowdays?
The most efficient drive for e-foil:
1st place - engine, propeller (highest achievable efficiency, highest acceleration, longest cruise)
2nd place - engine, impeller, nozzle - jet propulsion (top speed)
3rd place - engine, gearbox, propeller (highest stroke)
4th place - …
5th place - …
6th place - Counter Rotating Propeller (beautiful technical solution)
Such a propeller is not sold anywhere, no one has developed it!
@WNT Maybe I didn’t express myself very well, sorry!
I was not asking about commercial propellers I was more asking about the examples within our community of developers.
Can you share a link to your testing data? I may of missed your results.
Many Thanks,
Alex
Please provide me with proof for your guesstimations as all commercial designs clearly show this to be incorrect…
I do not have e-foil, I only deal with the research and development of new propellers. Current commercial propellers are completely unsuitable for e-foil. They are very cheap but have a very low efficiency of 15-20%. Such low efficiency does not make it possible to use the power of a very expensive battery and engine to have e-foil a high stroke and a long voyage. E-foil is a very special watercraft that needs a specially optimized propeller. Such a propeller can not be bought anywhere, it has to be designed by a hydrodynamics expert.
That’s why I’m willing to design a propeller for e-foil, but it’s got to be the best fully functional prototype of direct drive. The best direct drive should include an outrunner motor, one axial bearing (instead of the original radial bearing), one watertight seal and a special aluminum case (can not be bought, must be produced on a lathe) in which the engine is fully inserted. This creates a compact rotating unit that does not reach the water through the seal, and it is enough to attach the propeller. The motor shaft serves to be attached to the front fixed section of the hydrofoil leg. I think this solution is the only one for e-foil - it does not reduce the motor torque, it will provide sufficient cooling and easy maintenance (gasket replacement). For this compact rotary unit it is very easy to design a highly efficient propeller.
Perhaps someone finds and my concept of direct drive is modeled in 3D CAD. It is very easy. But there must be a way to get three wires from the engine from a rotating rotating unit. There are two solutions, one is very cheap, but a bit laborious, the other is more sophisticated, but more expensive. I would have modeled this concept of direct drive, but I would prefer to just model the propeller. The prototype of such a direct drive concept is inexpensive, easy to manufacture. If an optimized propeller is connected to it, it will become the best propulsion for the hydrofoil in the world.
I do not think this is a good topic for further discussion.
