The following text may have been generated by Optical Character Recognition, with varying degrees of accuracy. Reader beware!

January, 1925 a sailing ship with sheet metal sails, which would be operated by auxiliary blades fitted at the outer edge of these sails. When trials with these sails were made, Herr Flettner conceived the idea of having the Magnus effect tried in the wind tunnel. This is a physical phe- nomenon known for about 70 years and named for its first observer. In the fifties of the last century, Professor Magnus stated that a revolving cylin- der, when blown at by an air current displays the same qualities as a_ sail, that means, it exerts a pressure in an- other direction than that in which the air is blowing. But this effect had been neglected entirely until the problem was taken up by Flettner. The trials in the wind tunnel proved that under certain favorable conditions, the pressure exerted by the revolving cylinder is enormously larger than was supposed until! now and much superior to the effect of a sail. Indeed, the maxi- mum effect of a revolving cylinder of a certain area is about 15 times as large as that of the corresponding sail area. When this was found out, Flettner left the idea of sheet metal sails and de- MARINE REVIEW veloped the tower drive system. New investigations of comparative character were then made with ships’ models fitted with sails and with rotor towers. In these trials, the effect of sails was for the first time investigated in a scientific manner and proved to be of medium quality only when compared with the excellent effect of the towers. The result of these trials induced the shipowners, Donitz, Witt & Co., Ham- burg, who cwn a number of sailing ves- sels with auxiliary drive, to have the Buckavu changed for rotor drive to the designs of Herr Flettner. Some weeks ago, a new company, the Hanseatische Motorschiffahrts Co. was founded for the purpose of promoting the new drive. In this company, Messrs. Donitz, Witt & Co. have a large share and their ves- sels were taken over by it. It has been decided meanwhile that the other ves- sels of this fleet will be fitted with the new wind drive. The question which naturally arises from the impression of the recent trials is that of the economical importance of the innovation. Its advocates believe that a new drive has been created which requires scarcely any power, for that How Wind Acts on Tower NTEREST in the sailless ship. an- nounced by Anton Flettner, German engineer with several successful ma- rine inventions to his credit, has rested both on the ambitious claims made for such ships and the scanty information available. Early in December, much of the mystery was dispelled when a sec- ond trial trip of the first ‘rotorship’ was held and German and foreign engineers attended. Herr Flettner also has de- livered a paper before a German tech- nical society within the past few weeks, explaining his device. The following clear and complete re- port was prepared by the representative of the Liverpool, England, Journal of Commerce, who witnessed this trial trip in December. It will answer most of the questions which have arisen since this novel ship was announced. Having attended an: actual demonstra- tion of the Flettner rotor ship BucKau and subsequently inspected the vessel herself, one now feels in a position to comment on this extremely interesting vessel. In the first place it would be as well to state briefly the actual facts as to the effect of wind pressure on a rotating cyl- indrical tower, when such a tower is ro- tating about an axis perpendicular to the direction of the wind. A number of misleading statements have appeared on this point and the following notes may PERIPHERAL VvELociTY=U DIRECTION OF RESULTANT FORCE 7 WIND VELOCITY 1—PRINCIPLE WHICH LED TO DESIGN OF SAILLESS SHIP FIG. serve to make this point quite clear. In Fig. 1, a section is assumed taken through the cylinder at right angles to its length and we may treat the problem as one having only two dimensions. The wind velocity is taken=V and the peripheral speed of tower=U. The resultant force on the tower=I’ and this is acting in a direction making an angle of wx degrees with the direc- tion of the wind. When U x, that is, when the tower is not rotating, + — 180 degrees, and V and F are acting along the same line. F has then a value for any given wind velocity which is stated to be less than the F which would be exerted by a wind of the same velocity on the masts and rigging which have been replaced by the rotor tower. This statement should be treated with reserve, as it obviously depends entirely on the presumed eff- ciency of the rotor tower as compared with sails, and such efficiency as will be 23 needed to revolve the towers is insignif- icant, and which requires no crew for working it. The operation of the tower may be done by a single man occasional- ly serving the switchboard: Moreover, this drive is said to be much superior in effect to normal sailing. These are the main points, inferior ones may prove to be of importance in actual service. A probability exists that these qualities may lead te an extended application in the shipping trade. No doubt, this would be done in close connection with the screw drive. Whether it will. be preferable to have the wind power drive act as the main drive and the screw drive only to overcome calms, or whether the wind drive will only serve to in- crease the speed of steamers and motor vessels, would be answered by each in- dividual case as conditions are dif- ferent for different routes and different types of vessels. Study also would be necessary to determine the economic ad- vantages of converting sailing vessels, of fitting additional towers to such mechan- ically driven ships as are fit for the purpose, or of building new types of ships with new forms and ranging be- tween steamships and sailing vessels. Type of Ship seen later is not easy of assessment. It may be accepted, however, that the state- ment is true if the product of the height and diameter of the tower is about one- tenth the area of the sails which it re- places. This point will be referred to again later. If now we rotate the rotor tower, the direction of the resultant force F alters, and it travels round against the directions of rotation of the tower, the angle «+ being reduced from 180 de- grees to about 100 degrees under the most favorable conditions. The objective toward which Herr’ Flettner’s experiments were directed was that of reducing this angle x to 90 degrees, but so far it would appear that the best results obtained resulted in + being reduced to about 100 degrees. It is stated by Herr Flettner that with careful design + may be reduced to from 100 to 120 degrees, and it is reasonable to assume that one may fairly safely take + = 110 degrees as a basis of argument, and as a good average fig- ure for a successful design. In obtaining these results, experiments were made and curves ,plotted which showed the effect of varying the peri- pheral speed U while keeping the wind speed 7 constant, and it was discovered that when U is about 3.5 times the wind speed V7, the pressure effect is greatest, that is, the resultant force F reaches a maximum value. This maximum value is