THE ROTOR SHIP
HAS a. new and effective method of applying wind to the propulsion of ships at last been discovered ? For hundreds of years there has been no essential change in the design of ships and sails. Last week, however, we were treated to the portent of a German ship, the Buckau,' crossing the North Sea with the aid of rotors --that is to say revolving cylinders—in the place of Sails. It is true that the Buckau ' used. her motors which drive an ordinary propeller as well as her rotors, and, therefore, the test whether she could be successfully handled under rotors alone in an ocean passage seems to have been indecisive. On the other hand for at least the greater part of one day she was driven only by the rotors. She did not, we are told, go very fast then, but rotors arc still, of course, in the experimental stage, and the captain is reported to have said that in the rather lad weather which he• was experiencing -a sailing ship "would have been snugged down and " would -not have sailed any faster. ' The German paeans alter the `Buckates' first manoeuvres in the Baltic were probably exaggerated, :but the damping incredulity of many seamen who scoffed at the wonderful new vessel Was also exaggerated. Experi- -enced men at Grangemouth who have talked to the crew of the BuCkau ' have apparently come to the con- clusion that rotors after all cannot be laughed at.
Let us look at the principle of this new invention and See why it it that a ship with nothing but-two tall per- pendicular cylinders standing on her decks can be driven by the Wind, and manoeuvred almost like an ordinary sailing. ship." -Although-the invention is new the principle is old. -In the middle of last century Magnus,- pursuing 'the -earlier researches of Bernoulli, analyzed the Motion of a cylindrical object moving through air or water. When a bullet is fired from a rifle or a shell from a gun its drift down the wind is more than can be accounted for - by the actual -force Of the- wind. A cylinder, in fact, revolving in a current of air or water tends to move at right-angles to the current- and towards that side of the cylinder which is turning with the air current and not against it. We borrow this brief defini- tion of the Magnus principle from an article by a naval correspondent published lately in the Manchester Guardian as we could not improve upon its simplicity or compact- ness.
During the War Herr Flettner experimented a good deal in the steering of aircraft and invented a type of rudder, called after his name, which was equipped with small auxiliary vanes. These vanes caused the rudder to be affected by the air-currents and to be moved more _easily than it could have been moved without the vanes. The principle has since been adapted for ships' rudders. It was Herr Flettner's experiments with aircraft which led him to apply the Magnus principle to the propulsion of ships by wind. His large hollow cylinders are made of cast iron and have smooth surfaces. They are revolved by machinery. The revolutions of the cylinders do not of themselves, of course, do anything to drive the ship ; the cylinders are turned simply in order that the wind may play on a moving surface. Thus the Magnus prin- ciple is introduced.
Here is a description of the rotors at work which we take from the American Daily Science News Bulletin :- "They are spun on their axes by small motors—twenty horse-power is all the present ship employs. As they spin, they tend to carry a layer. of air around with them. In calm weather, this air would simply keep rotating about with the rotors, and nothing would happen. But when a wind is blowing, which would split and flow equally on both sides of the rotors if they were station- . ary, more of the air is turned with the direction of rotation than against it. Thatis, the wind is split unequally. The part that travels along with the surface of the rotor blows faster, momentarily, than the part that travels against the direction of motion of the other aide. The- wind that has its motion slowed down naturally tends to pile up pressure at-the point where the slowing occurs, while the wind that is helped to flow faster tends to lower pressure at-the point where the boost' is given. -When the wind is blowing across the ship, the rotors are revolved in such a direction that the pressure will be built up behind them and lowered in front, so that tho craft moves forward."
Herr Flettner has said that the effective .power of the wind when rotors are used is ten to fifteen times as great As with sails. That may be so but there are also obvious Jisadvantages. Before we come to them, however, we will look at the advantages. It is clear that there s a great reduction of labour in a rotor ship as compared with an ordinary sailing ship. The revolutions of the rotors can be started, regulated and stopped by one man standing at an electric switch. If he wants the .hip to go about he will simply revolve the rotors in contrary directions. How different this is from the business of changing . an ordinary sailing ship from. one tack to another with all the sheets, or braces, and stays to be: attended to ! Again; there is no such thing as going- aloft in bad weather to -get under control a - sail half blown away which is flogging itself into ribbons. Going aloft in a rotor ship Means only. climbing up a ladder inside one of the great hollow cylinders. It is evident that besides saving .labour rotors also mollify its conditions. Yet again, as. the rotors are not heavy —though they certainly look top-heavy—the motion of rotor ships may be expected to be easy in a heavy sea, as in fact the BUckau's ' motion was when she crossed the North Sea.
Now for the disadvantages. The reader may already have, suspected from .what- has. been said of the Magnus- principle that the rotors act- most efficiently when- the wind is on the vessel's beam: When the wind is right. aft the rotors, so far as we can judge, are of no use at all—they are. useless_ under. the very conditions which are generally most favourable to an ordinary sailing ship.- -Although the' rotor ship can go about like- any other sailing vessel and so can tack against the wind, it is probable that the act of going about involves more difficulties than are usual with ordinary ships. There arc times when no captain is sure that his ship will come about owing to heavy seas on the weather • bow as the ship comes to the. eye of the wind and loses way. She may misstay. and get. in irons. It is a common practice to avoid that trouble by wearing shipL—turning her round the other way with her stern to the wind. She will then make a certain, job of it though, of course, she loses a little ground. This method, however, is scarcely possible . for the rotor . ship as . the naval correspondent of the Manchester Guardian, whom we have already quoted, points out, for when the rotor ship brings the wind aft she loses its help. . She would then be in danger of taking a pooping .sea on board, being without the necessary speed to run away from it. Perhaps the only way for the rotor ship to go about in a difficult sea would be for her to move astern instead of ahead, which she can easily do. For this purpose, however, she ought to be double-ended.
The real issue. is not whether the rotor ship can wholly replace the sailing ship but whether rotors would justify their installation as an auxiliary in steam or motor driven ships. The special correspondent of the Man- chester Guardian who crossed the North Sea in the `.Buckau ' says that the turning of the rotors consumed only seven kilogrammes of oil an hour. The motors which drove the propeller consumed thirty-two • kilo- grammes an hour. In combination the rotors and motor drove the ship at a speed which would have required a,. much .higher _consumption of fuel had motors .alone been used. That is a remarkable fact. The chief defect of the rotors was that they did not revolve fast enough for strong winds. .
Unfortunately most of the trade winds on the great ocean routes do not blow in a direction favourable for rotors. How humiliating if, when running down your casting, you had to zig-zag half way across the globe to get the wind at an effective angle ! We have much yet to learn about rotors, but something remarkable has happened. It justifies not only the deepest interest but the hope that there are further improvements and discoveries to come.
Previous page
