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January, 1925 feet high originally and about 8 feet, 8 inches in diameter. The projected area of these two towers was reckoned to be equal to one-tenth the area of sail the vessel had previously been arranged to carry. The height of the towers was increased to 57 feet after a few trials, the result being that as the vessel now exists, the projected area of the towers is between one-eighth and one-ninth of the original sail area. The towers are situated, roughly, two- = 4 spetsunec ub ewe a F ¢d MARINE REVIEW supplied with current from a dynamo driven by a 45-horsepower diesel engine. The lower ends of the pivot towers are arranged to carry water ballast, presum- ably in case of necessity, but it would not appear that need had arisen for either of these spaces to be so utilized. The material forming the rotating sleeves is only about 1-25 of an inch thick for the main part, it being understood that this thickness is increased to about 1-16 of an inch at the deck level. Each aa © OFS 688 bd de bee sce ceree FIG4 Sequence of six positions turning with wind without helm. Fd. = Forward A = Aft. F = Force on Towers. FIG. 4—-TURNING TOWER SHIP WITH WIND WITHOUT HELM thirds the length of the vessel apart, the forward tower being somewhat nearer the end of the water-line than is the case with the after tower. These two towers are each rotated by an electric motor, and a tribute should be paid to those responsible for the design and building of this experimental installation. The pivot towers on which the rotating sleeves are supported are built up of plate and sectional material, and are themselves over 52 feet. high from the keel of the vessel, to which they are rigidly secured. At the top of each of these pivot towers are ball or roller bear- ings, through which the ‘weight of the rotating sleeve, and also the transverse pressure on the rotating sleeve are trans- ferred to the structure of the pivot towers. How Towers Are Driven The driving effect is transmitted to the sleeves through a 6 to 1 gear just below the top of each of the pivot towers. The motors are housed one at the foot of each tower, and are reversible direct cur- rent shunt wound motors of 11 kilo- watts, 220 volts, having a speed of 750 revolutions per minute These motors are sleeve is stiffened along its length and at intervals around its circumference by internal angles of light scantling. Taking into consideration the constructional dif- ficulties of making so light and so uni- form a cylinder, and also of mounting it in the ship, the care given the in- stallation will be appreciated when it is remarked that even when rotating at 120 revolutions per minute, there is an al- most entire absence of noise of any de- scription, while, were it not for the fact that a helix has been painted on each cylinder, it would be impossible to tell whether or not the cylinders were rotat- ing even at a distance of nine or ten yards. According to Herr Flettner, the total weight of the pivot towers complete with the cylinders is 7 tons, and it is stated that the old rigging which was removed, and which presumably included the masts, spars, rigging, and sails, was 35 tons. This appears a great saving, but sight must not be lost of the fact that it has been necessary to install a 45-horsepower diesel engine and dynamo, with the foun- dations, etc, to carry them, and that further it is essential that fuel should be carried for this engine. It is doubt- 25 ful whether the net saving of weight when all factors are considered will be at all approaching the 28 tons claimed. There is undoubtedly an increase in ini- tial stability. The control of the towers appears to be a simple matter. Two dials are placed on the control bridge, which dials indicate the speed and direction of rotation of the two towers. They, in effect, corre- spond to the revolution indicators or telegraphs in a twin-screw ship. The helmsman in the BucKav is positioned close behind the control bridge, which is abaft the after rotor tower, and he receives his orders directly from the master. While the means of control are simple, however, the actual determination of the steps to be taken in executing a maneuver does not appear to be quite so obvious, and the diagrams in Fig. 3 indicating successive positions of the ship and also the movements of the towers while turning into and through the wind, without the use of helm, will make this point clear. It will be noted that some care is necessary to correctly time the operations of stopping and reversing the towers, if the maximum advantage is to be taken of the turning effect which may be developed by their aid. Particular clain. is advanced by Herr Flettner for the rotorship on the score of ease of maneuvering when making progress against an adverse wind, and it is quite clear that with practice a master would save a good deal of time when changing course, as compared with the time taken by a sailing ship, with masts and yards, to go through the same maneuver. Turning With Wind The sequence of operations when turn- ing with the wind is shown in Fig. 4. Both of these diagrams have been pre- pared to illustrate the use of the rotors for turning the vessel without rudder effect. In a breeze, of course, it is pos- sible to make the turn more easily by using the rudder as well, but in light airs the effect of the rudder is very small owing to the small amount of head- way on the vessel, and the rotor towers are then of considerable value if one has no other auxiliary engine. During the demonstration on Dec. 3 the wind was very light, and the speed of the Bucxavu did not appear to exceed about 3 knots at any time. A _ large crowd of German, Dutch, French, Jap- anese, British and American marine men were present. Interest taken in England in the new ship is shown by the fact that representatives were present from the P. & O.:; British India; Alfred Holt; Fur- ness, Withy; Armstrong; Swan, Hunter; Hawthorn, Leslie; Vickers; Barclay, Curle; and Palmers shipping and ship- building companies.