Are cylinder ships a dead-end invention?

[kach22i]

An idea who's time has come...........again?

Are cylinder ships a dead-end invention?
http://openlearn.open.ac.uk/file.php...T307_1_rss.xml

In 1924 Anton Flettner, a German physicist, tested a prototype of one of his inventions, a rotor ship........................

Flettner discovered that when the wind blew at right-angles onto rotating cylinders a vacuum was created ahead of the cylinder and an area of high pressure behind, resulting in forward propulsion. Experiments showed that a rotating cylinder could extract up to 15 times as much energy from the wind as the same area of sail.

http://openlearn.open.ac.uk/file.php...T307_1_rss.xml

During the oil crises of the 1970s the idea was briefly revised and more recently found expression in the Cousteau Society's expedition ship, Alcyone (Figure 22). Built in 1985 the Alcyone uses two fixed cylinders with movable shutters and fans to achieve the same ‘lift’ produced by Flettner's more cumbersome rotors. When combined with modern computer control that switches between the Turbosail and the ship's engines according to the state of the wind, this system allows for a 35 per cent saving in fossil-fuel use.

[tinhorn]

Judging by your links, it sounds like we're overdue. Funny - I ran across some old mechanics magazines last week, and one of them had a story about these rotors.

[charmc]

More than one company is reexamining wind assist for commercial shipping. Makes more and more sense as prices and environmental concern both increase.

"Flettner had in fact, in our opinion, made a serious mistake. His rotors, spun round by a steam donkey engine, certainly gave plenty of thrust, but the aerodynamic efficiency, the ratio of thrust across the wind to drag downwind, was not much better than the original cloth sail rig of the barquentine. So the Buckau could broad reach beautifully, but was pretty terrible at going towards the wind.

And to make matters worse, there was no way to reduce the aerodynamic force from the rotors in strong winds. The poor Buckau could become “embayed” on a lee shore, desperately reaching backwards and forwards across the wind, unable to sail upwind and out of trouble. And finally, of course, if the steam donkey engine broke down or ran out of steam, there was no drive at all, just (too much) downwind drag.

The rotorship project fizzled out after one more ship, the Barbara, was built. We strongly believe that Flettner should have stuck to his original idea, because modern Walker-type thrustwings can survive hurricane strength winds, exert virtually no force on the vessel when put into neutral, and are highly efficient, so that wingships can sail very close to the wind. ...

The benefits of fitting wingsails to a commercial ship are primarily financial. Modern wingsails can reduce the running costs of the vessel by 20% to 40% in an existing vessel, and by 50% to 70% in a brand new ship designed to obtain the best results from wingsail assistance. ...

The picture above shows the 6500dwt mv Ashington, fitted with the first of a planned pair of Walker wingsails. Because of the oil price crash of 1986 the second, bow, wingsail was never fitted. The single aft unit was successful, and by itself could save 15-20% of her fuel.

A most interesting initiative by Wallenius Wilhelmsen in Sweden has developed the car carrier "Orcelle" concept, which includes, among a host of interesting new approaches, a full set of wingsails. Details of the "Orcelle" project can be found at www.2wglobal.com "http://www.shadotec.com/history.html

[amolitor]

Part of that is simply not true. Rotors have really nice properties with respect to generating lift in higher breeze. As I recall, lift goes down as the breeze goes up and certainly you can drop the RPMS to reduce lift if you like. The idea of going to weather with them is silly, and I don't think anyone ever proposed it. You use a motor to go upwind.

Also, that web page seems to be promoting wing sails for ships, which is a well established Terrible Idea for lots of reasons.

[Mild Bill]

What reasons?

[rwatson]

Yes, the idea of the rotors being uncontrollable is rubbish!
One of the reasons the "Buckau" got into production (as well as the Barbara) is that the aerodynamic drag of stopped rotors was less than the rigging of a clipper ship with all sails furled.
Also, the statement that "going to weather with them is silly" is ALSO silly.
They have effective pointing ability to within 15-20 degress.
Going downwind is not a problem - you do what all high performance cats and racing mono-hulls do, its faster to TACK DOWNWIND.

The reason that they were impractical when first used was that mechaincal tolerances caused destructive vibrations, and the costs ended up not being worth much for the fuel saved.

The late, great naval architect Lloyd Bergeson got a 42 foot motor yacht (the 17 ton Tracker ) converted around 1984. At 12 knot wind speed the craft recorded a 27% fuel saving. At 16 knot wind speed, there was a 44% fuel saving.
(Popular Mechanics January 1984)

I would not be surprised that with all the advances in modern design and materials that the Flettner Rotor did make a comeback.

[amolitor]

Well, Marchaj doesn't suggest that rotors point particularly well. The diagram in front of me suggests 60 degrees off the wind.

Hard foils don't work well across the very wide range of Reynolds numbers encountered by a sailing vessel. They generate far too much lift at high wind speeds, and almost no lift at low wind speeds. They need to be tended just as carefully as soft sails, and will cheerfully try to kill you when the wind comes up.

Rotors are much more friendly in those terms, since their lift curve flattens out as wind speed goes up. They need far less tending (they can be simply stopped if you like, and will generate no lift at all). They're more mechanically complex than a piece of cloth with a rope attached to the corner, though, and while they generate a lot more lift than cloth sails, they have correspondingly higher aerodynamic drag.

The most efficient system, overall, for the conditions a sailboat lives in seems to be fabric sails. With rotors you give up pointing ability (who cares, though, gentlemen do not sail to weather!) in return for a system that's trivial to manage. Hard airfoils will be either useless or dangerous most of the time, are likely to be as mechanically complex as rotors while needing as much or more tending as soft sails. For this, you get greater efficiency in a very narrow band.

[rwatson]

Originally Posted by amolitor

Well, Marchaj doesn't suggest that rotors point particularly well. The diagram in front of me suggests 60 degrees off the wind.

I relooked up my file, and 15-20 degress is indeed too optimistic. The actual plots show usefull lift to only 45-50 degrees. I must have been thinking of something totally different. It may have been correspondence I had with Joseph Norwood, where he was talking about apparent wind in faster multihulls. He had designed a particular proa configuration (successfully produced in the "harrigami" style proas), whose speed would move the apparent wind angle a great deal further ahead than the cargo carriers that were originally equipped.
LATER NOTE - Discovery magazine 1924 quoted the Buckau pointing within 23 degrees of apprent wind.

I have the original calculations from the Buckau showing everything from stability curves with the loaded towers, to projected performance curves. These were done in the "Goettingen experiments" prior to building the first 40 foot prototype rotor yacht.

In the calculations it illustrates the immense magnifying effect of powered cylinders. The effective force generated is in the order 10 times of a sail with an area equal to the width x height of a cylinder, spinning at around 100-150 rpm.
Mind you, this effect is only achieved by using "end plates", and a ridge half way up the cylinder. Earlier experiments that didnt use these 'gates' didnt get anywhere near the power.

Joseph Norwood also spent years disproving math that suggested that the power input to rotate the cylinders was far more than the propulsion power. He tested his calculations with several small scale models.

The other wonderfull effect of the rotors, is that maximum heeling resistance is reached at winds of 25mph, and in fact the moving rotors actually claw their way back upright towards the wind. When the rotors on the 'Tracker' were started in a light breeze, the boat actuall leaned *into* the wind.
This is important to commercial shipping, where the angle of the heel is ideally restricted to 6 degrees, which is why Cousteau's Alcyone had a multihull stern to prevent excessive heel.

[water addict]

Originally Posted by kach22i

An idea who's time has come...........again?

Not likely.

I did a semester term paper as a nav. arch. undergrad on sail/wind power for commercial trade. Got quite specific about stuff, and did engineering econ analysis.

The return was never positive, in fact it was always negative. The only time it was close, was if the cargo was being shipped with the wind aft of the beam- obviously not the case unless you are always sailing east in the southern ocean. Which is not a common trade route.

Sail power started to look like it might break even if fuel costs were enormously high. And I'm talking multiples higher than they are now- sorry don't remember the specific figures, and I don't have my paper anymore. I wrote it 20 years ago, and I'm not going to recreate the research again- it was a LOT of work.

[rwatson]

Well - we will never be able to pull it apart and discuss facts I guess. What a shame.

Its true though, variables like type of cargo, port profiles, schedule constraints, cost of auxilliary power gear, wages, deck space are all major factors over and above fuel savings.

It will be a while before any serious work is done on sailpower I think.

[amolitor]

It's perfectly possible to route shipping do it's downwind all the way, this was done for centuries. Of course, people were more patient and willing to wait for seasonal trade winds to kick in. However, even today it's possible to route shipping through largely downwind routes.

That said, fuel costs per ton-mile are incredibly low on (for example) a large container ship, so it's quite hard to recover much money no matter how awesome your sailing technology is.

[wet feet]

I would be able to visualise some kind of future for either the Flettner rotor or some kind of wingmast rig if it were possible to easily reef them.To add another system of some complexity and its resulting cost in addition to having an engine for the days when the wind doesn't blow will have to be paid for in some way.

[amolitor]

You don't need to reef a rotor, though. The lift drops off as the wind increases.

[wet feet]

And with a force ten on the beam?

[amolitor]

So what? The rotors are smooth and not that gigantic. Sure, you have to take them into account, but people put superstructures on boats and don't freak about about having to reef down the bridge.