Everything Old is new again - Flettner Rotor Ship is launched

I haven’t seen a savings to investment ratio (SIR) to see a metric that measures how well an investment can recover its costs through it's savings over it's lifespan with journaled peer review articles and empirical research. Not saying that there isn't. But "frothy eloquence neither convinces nor satisfies me, you have to show me." - Congressman Willard Vandiver in 1899.

 

Those link didn't work, Try using the Link tool instead of just cut and paste.

But, I found the paper, with a google search. Here is a working link
https://iopscience.iop.org/article/10.1088/1742-6596/2265/4/042057

Here is the Conclusion



The results were VALIDATED !

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As far as your claim about it being non-competitive with the normal sail rig,
This wasn't a competitive study, no actual like for like performance comparisons were attempted, with a sail Hobie racing a Rotor Hobie , as I suspected.


Now, lets see what speeds are expected from a SAIL version of the original Hobie Cat and a bigger version , at 10 knots of wind speed

On the Wire - Feature https://www.thebeachcats.com/OnTheWire/westnet/_lpm/hobie/archives/v1-i3/feature3.htm


Allowing for the extra weight of the batteries, control system and motors, and the Rotor mounted on one hull. , if I plug in the figures from the open source calculator
You will see that the expected power output at ten knot wind speed, is about 1.8 HP, which would fit with the say 5 knot performance in the paper, on the loaded boat. Or 4 knots in the test, EXACTLY what they intended.





Now, if I was designing a Hobie, to race other Hobies in 10 knots of wind, I would increase the Rotor to .6 metres, instead of .45, and produce 1/3 more Power.



So. by increasing the swept area from 3.8 sq metres to 5 sq metres, we increase the output by ~ 1/3.
Who knows what the optimum rig dimensions would be to be competitive with a sail Hobie, but they are not what the analysis rig used.



So the normal Hobie rig, with about 21 square metres, produced double the speed of a Cylinder of (2.8 x .45) 1.26 sq Mm of cross section, or 1/4 full swept area.

Sounds pretty competitive to me.

 

I'm not sure what this post is about, but if you are implying that the full proof of a concept is in the long term real life application of a principle, then there is plenty of evidence in the form of hard cash orders.



And July 24 - a recent completed launch

 

1- The theoretical results were validated in that they show the rotor rig produces as much power as they claim, BUT the theory is disproven because the speeds achieved show that the rotor rig is not half as powerful as the normal Tiger rig as they claim.

The authors have therefore under-estimated the power of a "conventional" rig dramatically, which makes the comparative power of the rotor appear much better.

2- The Hobie Tiger is not a Hobie 16. The Tiger is similar in all-round speed to the Tornado. The polars that you show indicate that a Tornado does 14 knots when reaching in 10 knots. The Tiger is rated 7% faster than that version of the Tornado.

The rotor rig achieves 3.8 knots on Tiger hulls in 9.4 knots of breeze, and is therefore (according to your sources) about 22% as fast as a standard Hobie Tiger. A speed reduction of close to 80% shows that the rotor rig does not produce half as much power as a standard rig, ergo some of the paper's calculations are wrong.

3- According to your sources, the polars, the Tiger with rotor is about 34% of the speed of a Tasar when reaching in 10 knots of breeze. In such conditions, a Laser Radial/ILCA 6 is about 90% as fast as a Tasar and therefore about 2.6 times as fast as the rotor Tiger. A Laser 4.7/ILCA 4 is fractionally slower than the 6/Radial in such conditions.

So your sources confirm that the rotor Tiger is very slow even compared to a much slower Laser hull driven by a soft sail about 1/3-1/4 as big as that of a Tiger's standard rig. Therefore we see, once again, that the calculations are incorrect - if the very efficient Tiger hulls were being driven by a power source half as powerful as the standard Tiger rig then they would not be going far slower than a far less efficient hull driven by far less efficient rigs.

4- As an estimate, driven by gut feeling and some quick calcs, the Tiger rig in 10 knots of breeze would be producing about 2.5 times the heeling moment of a Tasar rig while creating a similar increase in power and considerably less drag. So if the rotor was producing half the power of the standard Tiger rig, as claimed, the Tiger hulls would be going much faster than the Tasar does according to your source. In the tests, the Tiger hulls went about 34% as fast as a Tasar does according to your source.

Therefore we see once again that the study dramatically under-estimated the real power of the "conventional" rigs and therefore the comparison of the rotor rig versus the conventional rig is problematic.

4- Comparing the polars you provided to known performance yardsticks indicates as that the Tiger with rotor is reaching in 10 knots at about the same speed as an Optimist with 3.3m sail. Clearly, then, the study is wrong when it says that the rotor rig is producing half the power of a standard Tiger rig. The only way a Tiger platform can be going only as fast as an Opti when reaching in 10 knots is if the Tiger's rotor rig is producing less power than a 3.3m spritsail . Therefore the author's calculations about the power produced by the "conventional" rig are clearly wrong.

In summary, the calculations may be showing that the rotor rig is producing as much power as the author's calculations say, but their calculations for the power produced by "conventional" rigs are clearly wrong. Therefore the rotor rig is NOT as powerful in comparison as they claim.

 

Do you understand the concept of objective data? Sorry to be so blunt, but you keep on producing press releases from vendors and related bodies as if they are objective data. A press release from an interested party is about as reliable as a political party advertisement or ad from a real estate agent or used car dealer. You cannot convince reasonable people by showing them press releases from interested parties, particularly when previous claims about the same invention have not come to fruition.

It's fascinating to see how often the same pattern arises with respect to rig design - people just keep on producing press releases and claiming that they are proof. I wonder what it is about rigs that causes this illogical behaviour?

 

If you don't think that an investment of 100's of thousands of dollars, based on the previous performances and proven savings isn't some kind of "proof", then I don't know what the heck you will accept.
There are dozens of actual working, long term installations, and more being installed.
What on earth would one need to do to prise $200,000 out of your pocket ?
The same evidence is what gets these companies to do it.

"as reliable as a political party advertisement or ad from a real estate agent or used car dealer."
Complete nonsense. There are at least 3 working videos of commercial installation on this forum, and if you go to Norsepowers web site, at least a dozen working installations.
News - Norsepower Rotor Sails™ | Wind Propulsion https://www.norsepower.com/news/

 

Wow, total logic snap there.

"the calculations may be showing that the rotor rig is producing as much power as the author's calculations say," - so what is the problem?
If I change the Rotor configuration, I can "dial in" ANY performance level I want , including Tornado performance.
Even if they got the sail performance wrong, it makes no difference, unless you are in a race.

It doesn't MATTER how well the estimate the original sailing performance. As I showed, IF they had wanted to match a sail rig, they only have to tweak a few Rotor dimensions, and get parity with sail configurations.

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"the rotor rig is not half as powerful as the normal Tiger rig as they claim."

That's NOT what they said.



They said the "lift co-efficient" was equivalent to HALF that of the Hobie, NOT the overall boat performance.
If I loaded a Hobie with a sail with battery, electric motors, actuators ands control gear, THEN you could make a useful comparison.

 

Car manufacturers invest far more than that - however that investment is not proof of the claims made by those involved in producing the cars. Claims from a company involved in selling rotors are not disinterested objective proof, just as claims made by Ford or Mazda about their cars being better are not disinterested objective proof.

Plenty of companies spend vastly more than $200,000 on various devices. That does not mean that those devices are as efficient as claimed.

I have said about two or three times what sort of proof I will happily accept - normal scientific "proof" as demonstrated by peer-reviewed studies by disinterested parties that include actual comparisons that can prove or disprove the claims being made.

 

How much time have you spent sailing a Tiger? How much time have you spent sailing a comparable craft? How much idea do you have about how a loaded-down Tiger compares to the craft in the polars you showed?

You refer to a Tiger being loaded with "battery, electric motors, actuators and control gear". If that added up to the 160-170 kg of a typical Tiger crew then it merely shows how heavy the gear required for a rotor is. However, the photos show that the gear added up to a lot less than a typical Tiger crew. The rotor boat was therefore almost certainly dramatically lighter than a typical Tiger (which it clearly was according to the photographs) and therefore the extra displacement is irrelevant - the rotor Tiger appears to be dramatically lighter than the comparison vessel and in 10 knots of wind that can make a significant difference.

The paragraph comparing the rotor to the standard Tiger rig is as follows;

"The initial rig of the Hobie cat Tiger catamaran (a 17 m² mainsail and a 4.15 m² jib) was replaced by a Flettner rotor in the second prototype. The rotor height is approximately 2.8 m and the diameter is 0.45 m. Taking into account the high lift coefficient of Flettner rotors, it is approximately equivalent to half of the surface of the original sail."

The subject of the paragraph is the rig. The final sentence states that taking into account the lift coefficient, "it" (meaning the rig which is the subject of the paragraph) is approximately equivalent to half the surface of the original sail. The paper does NOT say that the lift coefficient is half that of the original rig, it says that once the lift coefficient is considered, the rotor RIG is equivalent to half the surface of the original rig.

If the subject of the sentence you quoted ("Taking into account the high lift coefficient of Flettner rotors, it is approximately equivalent to half of the surface of the original sail.") was merely the lift coefficient then the sentence is illogical; there is no reason to include the passage "taking into account" or "it" or "the surface". The sentence would merely read "the high lift cofficient of the Flettner rotors is approximately equivalent to half the original sail". It is against all normal logic to claim that an author included highly significant passages that were totally irrelevant to what you allege they were trying to say.

Even if something has suffered in translation, here we have a 2.8m high rig with a far higher weight than an Optimist rig of similar height AND a motor, that is driving a fast cat platform about a fast as an Opti is driven, and dramatically slower than a Laser 4.7 goes. That is not evidence of an efficient device in many ways.

If they got the sail performance wrong it DOES change things. It shows that the basic calculations of rotor rigs may be incorrect. It may show that other rigs could be more effective in driving merchant vessels. If a rotor rig is significantly less powerful for its area then maybe merchant vessels should be using other rigs for auxiliary power. Why not keep an open mind and use the normal scientific methods of assessing these devices?

I don't know why you are so invested that you misquote people on this forum, as you did to me earlier, and make childish insults. A while back you were making disparaging remarks about those trying to demonstrate rotor rigs, if I recall correctly, and saying that you were going to make one to demonstrate them. I haven't seen the results of your demonstration. I am totally open minded about rotor rigs but that doesn't mean accepting the claims made by those who sell or buy them, just as I don't accept the claims of Ford or their fleet customers about why their cars are better, and I don't accept the claims of Beneteau or the charter companies who buy them about their craft.

Just as with other "alternative" rigs the point is simple - back up the claims in a normal scientific way with normal tests against a reference craft at the same time in the same conditions. This is not very difficult, and should be the norm for anyone wanting to have their claims accepted.

 

Oh, and furthermore - re "total logic snap" - grow up, stop acting like a stupid child and using moronic insults on a discussion forum about boat design. You have already proven with your mistakes on your spreadsheet that you can be very wrong in aspects of this topic, you have already misquoted people because you apparently do not know how the language works or cannot read correctly, so stop the stupid insults and discuss technical issues correctly.

The logic is clear - if the rotor rig's performance compared to "conventional" rigs is not accurately assessed then the rotor rig's propulsive power may not be properly assessed, and it may also be better for merchant vessels to use other rigs.

The fact that the authors claim that a Hobie Tiger requires a certain power to drive it at a certain speed is NOT proof that their calculations are correct, either in terms of the required power or the power of the other possible rigs. For you to ignore such points and resort to childish insults is ridiculous.

You did not "show" anything. You made unsubstantiated claims based on a spreadsheet of the type you have shown that you repeatedly make mistakes filling in, which rests on unproven claims about rotor rig efficiency. If the underlying claims about rotor rig efficiency had been proven in boat-on-boat trials by objective disinterested people using comparable rigs the this discussion would not be occurring.

You are also bringing in polars that were only produced by software, dealing with classes including two in which their own designers have said that their performance cannot be assessed by software, and are said by their creator to possibly not be accurate and that do not accord with databases of comparative performance. So this is layer upon layer of unproven claims and calculations made on different bases, and yet you abuse those who merely say that the normal scientific process of assessing claims should be made.

Those polars are clearly unreliable as anyone with a reasonable grasp of the comparative speed of the craft involved can tell straight away, although I didn't raise that earlier to avoid confusing the situation. However, the fact that you raised them indicates, to be blunt, that you have very little idea of the comparative speeds of sailing craft. That seems to grossly affect your ability to assess the comparative performance of the rigs that drive them.

The lack of accuracy of the polars you raised merely shows the enormous problems involved in doing studies in this area that do not use simple boat-on-boat testing.

At a much less accurate level, the other day we got GPS recordings of the speed of a Walker Bay 10 with two people aboard and driven by a 42lb thrust Minn Kota. The WB 10 got 3 knots under that motor which is equivalent to about .5hp. The claim that the far more efficient Tiger platform requires over three times as much power to go 25% faster therefore appears to be very dubious to me.

Science and objective assessment don't work well when people put layer upon layer of assumptions and tests, gained on very different subjects, upon each other. That brings in too many variables. Good science rests on objective data obtained under properly controlled conditions with a minimum of variables. Don't be so silly as to abuse those who apply those standards instead of believing sales talk and unsubstantiated claims - especially when there are abundant ways of carrying out proper tests.

 

A Chinese company is now building Flettner Rigs






About Dealfeng - ZESTAs https://zestas.org/about-dealfeng/

 

Confirming the 2013-built bulker BERGE NEBLINA now retrofitted with four 5x35m Anemoi's folding rotors:
https://www.shipspotting.com/photos/3788821
https://www.shipspotting.com/photos/3788822

 

With more to come



"Leading wind-propulsion technology provider Anemoi Marine Technologies Ltd. (“Anemoi”) and U-Ming Marine Transport Ltd.’s (“U-Ming”) have signed an agreement to install four Rotor Sails on one of U-Ming’s 325,000 DWT Very Large Ore Carriers (VLOC).

The installation work is expected to be completed at the end of 2025, with fuel and emission savings of approximately 10-12% anticipated on deep-sea routes between China and Brazil, South Africa, and Australia."

U-Ming Marine appoints UK technology provider, Anemoi, to install Rotor Sails on a VLOC - Anemoi https://anemoimarine.com/uming-marine-appoints-uk-technology-provider-anemoi-to-install-rotor-sails-on-a-vloc

 

Fletner rotors don't go upwind, that's the flaw

 

Neither do sails. What is your point ??

Meantime, the actual study done for these diagrams says Rotors are a "compelling case"



https://www.researchgate.net/public...Commercial_Ships_A_Techno-Economic_Assessment