When will leisure craft adopt the new sailing systems?

Thanks Rumars, that was very interesting.
Not by way of criticism, but observation. Like every other "Small Rotor" demonstration, the Rotor sail is in mill pond conditions.

They start with a video of a great fleet of sailing dinghies, shooting about in perhaps 15 knots of wind. Then have the sense of humour to demonstrate the Rotor where there isn't even a ripple in the water.

That is EXACTLY why I decided to build my own prototype. I have NEVER seen any small rotor being used in anything but sub 10 knot conditions.

There will never be any change unless the engineering creates substantial Rotors that can face realistic weather conditions, say up to 22 knots for leisure craft.
The whole planned benefit of Rotors is their controllability in difficult conditions. Light winds can be a fair proportion of sailing conditions, but there is no problem to solve in that scenario.

 

Rwatson, there is a reason why you don't see small rotors used in high winds. As you probably know, power consumption increases with wind speed, and this increase is not linear. I don't know how exactly rotor size, input power and wind speed corelate, but it's not a simple equation.
Small boats have small motors, by the time you install a motor big enough to keep the flow attached in higher winds, the rotor has become a sail assist instead of primary propulsion. Even with electric motors there is a problem of efficiency, one designed to be efficient at high power levels will not be it at low power. Of course this can also be solved with multiple motors, or stepped gearing, etc. but its added complexity.

I suspect this is one of the reasons you see such varied accounts when it comes to overall performance. The entire installation has a pretty narrow band of conditions in wich it functions well and is also economically advantageous compared to pure mechanical or conventional sail propulsion. If you have a stable route with known wind patterns you can design the rotor for the average conditions and do well, but you end up with a one trick pony.

 

Ah, but it IS simple
I have posted the calculations in several places, including my Rotor building blog. Thanks to some very smart people who have helped a lot.

You have touched on one key factor - understanding the speeds. Not ONE of the Rotor projects I have read anything about has actually calculated BOTH power input, and power output. They just guess.
Electric motors are pretty much as efficient at high and low speeds. The motor I have is good for 11,000 rpm. but my operating range is 400 to 800 rpm, so I have all the gearing room in the world. At winds over 20 knots, I may lack power to run the Rotor in the wind, but since I am only using 250 watt motor, I don't need to go much larger in an electric motor to cater for bigger winds.
The Rotors don't have to spin to "attach flow". That happens from zero to any speed up to probably 20,000 rpm. Its not like wings that have to be at optimum angles of attack - Rotors are round.

You once again highlight the problem of amateur design. Actually bothering to do the calculations.
I don't for a moment subscribe to the idea of the Rotors having to be fine tuned for weather conditions. I DO know that they should be designed to suit the vessels they are placed on, but EVERY boat is a "one trick pony", designed to perform in a predesigned range of conditions. If there is not enough wind, from prevailing directions, auxiliary wind power is a waste using any type of rig.
For amateurs, with no strict timetables, that is way less critical.

 

Since there seems to have been no public data that showed it actually worked, there's not much to be up to speed on.

The video does seem to take the "shoot a vid in no wind and avoid proper demonstration" tradition to a new high, though.

 

RWatson it will be great to see a rotor sail on a small craft in rough conditions.

When looking at windage, as I noted earlier I'm confused about the calculations you gave earlier which showed that a total rigging wire area of .546 metres gives 68% of the windage of a rotor with the same Cd but almost 15 times the area. Am I missing something basic (which is very possible as I can't see all the input and I have the maths ability of a dead flea) or is there an error in the spreadsheet?

By the way, one of your earlier sources said that the pic below was of the US experimental rotor boat but numerous other pics, including contemporary ones, make it clear that the rotor yacht is one of Flettner's German boats, sailing against a Nationale 30 QM Binnenklasse.


.

 

Yes, surprising, isn't it. Round rigging Rod, and especially .
This site has some useful info, including this gem.

You would have to be more specific with the "earlier source", but from a cursory search, I think you may be confused with an article that mentions and illustrates two Rotor Yachts together, one the German racing yacht, the second an American experiment, page 32 of
flettnerpat http://www.homepages.ed.ac.uk/shs/Climatechange/Flettner%20ship/Popular%20Science%201st%20American.htm

 

No, it's not that it's surprising that round shapes have high drags - I just can't see how out of two round shapes (a rotor and rigging) the one with about 15 times the size (the rotor) has 68% of the windage according to the spreadsheet you put up.

They are both round, so they should have the same Cd, so why does the vastly smaller rigging have 2/3 the total drag of the vastly larger rotor?

I'm not the one who is confused about the boat in the pic. The article you quoted earlier, which I reproduced above, has the clear caption "Figure 3. Kiernan and Hastings Rotor Yacht" but the pic shows a Flettner boat racing in Germany, as shown by the original caption on the same pic in your latest link and by the fact that the rotor yacht is racing a conventional German boat, by other pics of the Flettner boat in Germany, and by the pics of Kiernan and Hasting's actual US boat. It's not a big deal but it may show that the authors of the journal article were a bit sloppy.

 

Please tell me the Post number, so I have a chance of clarifying

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Well, I guess this is why its great to have an open forum discussion, because we have to check and look deeper if we see anomalies.
The big difference in figures was a complete error on my calculations. I have posted the bad formulae here ,and a revised configuration below.



The Rotor provides more wind resistance by a factor of 4, compared to a single masted aero-shaped rig with zero sails (furled on the boom or on the forestay). In storm conditions, this is only ~300 pounds, barely a big sailors bulk.





But also, considering that the righting moment of a rig ten metres high, compared to one less than half the height, that doesn't need rigging sails to get underway, I think its an acceptable configuration for decent sized boats that have to be left at moorings.

 

Sorry rwatson, your Excel calc is still wrong. Take a look at the "H" column; the Cd says 0.015, should be 0.15. The frontal area says 0.11 meters; can't be since area is squaremetres, and with a height of 10 m, the mast dia would be 11 mm, which I sincerely doubt.

If the mast dia instead is more reasonable 0.11 m (110 mm), the total wind force on the bare rig would be ~150 N, which is 1/8 of the rotor value. And 1200 N halfway up a 4 m rotor, plus some 0.5 m above wl gives a heeling moment of 3000 Nm. A sailor weighing 75 kg (equals a downforce of ~735 N) must hang out 4.1 m to compensate for that in a storm; not particularly comfortable, I'd guess.

 

Another approach from Bernhard Kohler published in MULTIHULL INTERNATIONAL 190, Dez 1983. As
he has studied math and aerodynamics there are a few interesting numbers.

 

Thanks for that checkup.
"the Cd says 0.015, should be 0.15"
Yes indeed, and not only that, I discovered it wasn't even being referenced correctly

The Area of the mast also needed correcting, as you observed.

I'll put the crew position required in 37 mph winds in the operating instructions

After all those, we have this new scenarios, using more typical Mast Cd. It looks like it would be safe to moor the average yacht with a Rotor present.



and out of curiosity, I did one for a traditional Round mast, for those interested.


It occurred to me, that I am using Stormy wind speeds, so I did a "normal wind speed" one as well

 

So once again, someone built a rotor rig and then never seems to have released significant information about its performance.

How many times will this happen before someone just goes out and proves the claims they have made by regularly sailing against other craft in a manner that allows objective comparison?

When there have been so many well-publicised trials and builds but no objective information with third-hand verification, what does it mean about the accuracy of the claims made? If the rig works so well, why do we never see the boats remain in use?

 

I guess that's why I do the calculations and experiments, to reveal the hidden "gotchas"

But mind you, its now easy to see how the claims that Rotors have less wind resistance than traditional commercial sailing boats is correct.
Imagine the resistance of a four masted traditional cargo schooner, with round masts, stays, ratlines, baggywrinkles, furled sails etc in a big blow. Either out to sea or anchored.
They weren't lying.

But now on the other hand, the fear of Rotor ships being prone to severe windage at anchor is vastly reduced.

The calculations show that a larger yacht, can virtually leave their sails set at anchor, and incur manageable upgrades to their ground tackle.



Even at Hurricane strength winds, we are looking at under 2 tonne of of pressure, which can be catered for by larger ground tackle. Also, flogging ropes and sails while at anchor is a thing of the past.



Then, to take the ability of having fully set "sails" at all times to its other extreme, how many traditional sailing craft can up anchor and sail away on high winds at the push of a button, without the flogging sail raising exercise ?
I can recall a few stories of yachts finding that they are suddenly on a lee shore from a strong wind shift, and start dragging anchor. They cant put their sails up easily, and because they have to reef in the strong winds, so then they cant claw their way to windward.
I can certainly remember cancelling sailing trips because the winds were just too uncomfortable for sail handling from a mooring or wharf.

 

For people who are interested in results of scientifical research:

The aerodynamic forces and wake flow of a rotating circular cylinder under various flow regimes
Author links open overlay panel
, , , ,Redirecting https://doi.org/10.1016/j.jweia.2022.104977Get rights and content


Der UNIKAT (Boot mit Flettner-Rotor) - Institut Physik - Europa-Universität Flensburg (EUF) https://www.uni-flensburg.de/physik/forschung/energie/der-unikat-boot-mit-flettner-rotor?sword_list%5B0%5D=we&sword_list%5B1%5D=best&sword_list%5B2%5D=du&sword_list%5B3%5D=mensch&cHash=a404ba8196fcbd6aa193d61557645b69

One of the results: If the peripheral speed of the rotor reaches four times of the windspeed the propulsion can not be increased. This propulsion saturation effect has been unknown.
When I contacted the Prof. he was happy to tell me that the rotorboat
had reached ten knots. But mbuli with her oroginal SA has been clocked with 15 kn.



Proa Sailing: Mbuli, by John Harris http://starrigging.blogspot.com/2010/11/mbuli-by-john-harris.html

Mbuli: Ultra-light Pacific Proa Beach Cruiser by John Harris https://www.clcboats.com/shop/boats/wooden-sailboat-kits/proa/mbuli-pacific-proa-beach-cruiser-plans.html

 

Great information.

I wasn't able to find the section that said "If the peripheral speed of the rotor reaches four times of the windspeed the propulsion can not be increased."
If you can make it easy to lookup, that would be good.

EDIT: "This propulsion saturation effect has been unknown."
It looks like he was mistaken about it being unknown. This effect was actually commented on by Flettner himself.
It is news to me though



https://www.kimerius.com/app/download/5784789559/Testing the Flettner rotor in actual flight.pdf


" the rotorboat had reached ten knots. But mbuli with her original sails has been clocked with 15 kn."

The original sail plan for the Proa was 18 square metres.
The new Rotor is less than 1/7 th the original sail area, in profile. (2.8 SM) 4M x .71 diameter. This give a maximum lift co-efficient in a 15 mph wind, of 9HP.

If he had made the Rotor 1 M in Diameter, he would get 12 HP (4 SM) in the 15 mph wind, a 25% increase.

This illustrates the need to properly match Rotors with desired Hull speed.