3,000-ton Rotorship may Revolutionise Cargo-carrying.

Star (Christchurch), Issue 17853, 22 May 1926, Page 17 (Supplement)

3,000-ton Rotorship may Revolutionise Cargo-carrying.

Flettner’s Invention applied to larger vessel recently launched.

By

Granville Whittlesey,

Special Correspondent of the “Star" and the North American Newspaper Alliance.

Copyright by the “Star” and the North American Newspaper Alliance. All Rights Reserved.

KIEL, April 13.^ LAST year Anton Flett tier's rotor ship Ruckau, now the Raden-Badcii, crossed tlie North Sea from (Icrmany to Scotland, and returned. The Press reported the experiment with varying degrees of and for the most part expressed itself as frankly condemnatory or gravely doubtful of the future of the invention. Since that time little was heard of the rotor ship until her departure for New York early this month on a test trip, which proved successful.

However, in this seemingly dead period the invention made great progress. Only a few weeks after Flettner’s craft returned to Hamburg, the Herman Mercantile Marine took up the idea with the construction of a 3000ton rotor ship.

This vessel, now nearly completed, will be launched in the middle of this month < April). She will have a length

of 270 feet with a beam of 39, and when fully ready to go to sea in August, under contract to the Robert Sloman firm, of Hamburg, will mount, as shown in the accompanying picture, three rotor towers constructed of lautal, a new alloy of aluminium recently developed in Germany.

These three rotors, 12ft in diameter and rising SOft above the waterline, will develop 2000 horse power in winds above 10 metres a second (slightly more than 20 miles an hour), and when developing such power will give the ship a speed of 11 knots. The rotorpower equipment is to consist of a 35 horsepower electric motor for each rotor, giving a tower speed varying from 100 to 150 revolutions per minute. Current for the motors will be furnished by a Diesel-driven generator unit of the size used for providing

electric power on ships of this tonnage. Two 560-horse-power Diesel motors capable of giving the ship 10 sea miles per hour will make up the main driving equipment. These two units will be connected to the single propeller shaft through clutches of the oil turbine variety in order that one or both may be easily connected or disconnected.

The new ship is to run in competition with two sister ships, Diesel-driven and of the same tonnage and hull construction. Like these, she will be first tried out in the Mediterranean fruit trade and later on a voyage to the west coast of South America. Thus the new rotor ship will enter upon a

contest to prove that she can cut down on the fuel burned by an identical vessel not drawing power from the wind. However, so sure are her designers that the new ship will tisc less oil than her sister ships, they have provided her with tanks of only 60 per cent of the capacity of these others; and further estimate the rotors will effect economies in oil consumption varying from 40 per cent to 60 per cent of the quantity burned by the sister ships.

Beyond this, neither the Slomans, who arc an old Hamburg shipping firm, nor the German Mercantile Marine wish to make any prophecies as to what they expect of the new ship. Suffice it to say that the building of the ship by the. German Mercantile Marine and its charter by a merchant skipper show a genuine belief in the practical nature of the invention. Shipping men who regard the rotor ship unfavourably are bringing up the point that the early steamships also used the wind as an auxiliary, but gave it up on account of the fact that when the steam engine became reliable the power it furnished was so great as to make that furnished by the sails negligible. Therefore these ask why, if the Sloman firm wishes to use the wind, does it not revert to sails insteam of using these new-fangled rotors? The first answer lies in the accompanying scale drawing Xo. 2, which shows the sail area contrasted against the area of three rotors required to develop 3000 horsepower. That is, while it required a rotor projection area of 1914 square feet to provide this power it would require a sail projection area conservatively estimated to be eight times greater to do I’kewise.

Such a sail equipment could not be put on the ordinary 3000-ton mer-, chant ship without giving her keel or at least ballast, to counterbalance such a great top hamper. Even if it were done it would need a crew of at least thirty men to handle the sails aione (construction of the ship would make only square sails possible) ; and maintenance of rigging and crew would eat up any 40 or 60 per cent to be made in fuel savings bv so equipping the vessel.

It is on the fact that the rotor completely overcomes all of these objections that Flettner bases his claim for the invention. The installation of rotors requires little change in any ship now in the merchant service. The illustration of the new 3000-ton vessel shows that no rearrangement of deck fittings is in any way necessary. No increase of crew is required as the control of the rotors is managed by a set of handwheels on the bridge. The upkeep is a matter of painti.-g the towers.

Thus viewed from the basis of a comparison with the old sail-equipped steamers of our grandfathers, the rotor equipment is strikingly different and superior. Again, looked at from the standpoint of the straight sailing ship there are equally interesting differences. The chief of these are that the rotor sailing ship shows almost no tendency to heel, and that, given a breeze of increasing velocity, the rotors quickly develop their maximum power

and ~regardless of how much stronger the wind mav grow do not increase that power. The first of these differences depends on the fact that the rotors offer very little resistance to the wind when still. They offer even less when in rotation, for then most of the wind’s force is twisted, so to speak, from- side pressure to fore and aft pressure- and suction. Ihe second difference, that of fixed power output, is shown graphically in the accompanying cut (No. 3). The horizontal axis represents the wind velocity in metres per second. The vertical axis represents .units of force in kilograms. Curve j A. shows development of rotor power at increasing wind speeds. Curve B, • the same of a sailing vessel. It can Ibe seen that the maximum for the ! rotor is reached at a wind speed of a j little more than 10 metres per second, I and from there on remains constant. In fact, if the curve were to be carI ried out to greater wind velocities it would eventually be found to drop. This is because the greatest development of power comes when the rotor surface speed holds a relation to wind speed of 3 to 1. When this ratio is decreased the power does not increase, but eventually falls off. For those curious* it may be said that if this best ratio were to be maintained at higher wind speeds, by correspondingly higher rotor speeds, greater power would be developed. However, with present construction methods, 700 horse-power is about all that a rotor 4 metres thick ,and 17 high, such as is going on the new rotor ship, can develop without having something to carry away. A bigger rotor coulcj be put to a greater strain. Thus it was first contemplated to build a single' tower on , the new ship 7. metres in diameter and i 27 high. This would have>been able to develop nearly 2000 horse power in itself. But the necessity of making very heavy bearings prevented this : original plan from being earned out. These two points, therefore, lessened resistance and limited' power output, stand for two great sailing advantages in the rotor ship, namely, that one [ never has to shorten sail in a gale and ' that one never-need worry about can- ; vas or spars carrying away by being ‘ subjected to too much pressure, i.e., ' developing too much power in a high 1 wind.

It is in relation to these points of safety, economy, ease of installation and simplicity of operation that the coming 3000-ton rotor ship will be

o .. 20.- . 30 Power and resistance curves of sailing* ship and rotorship—(a) Rotor power* development curve. (b) Sailing ship's resistance to wind without sails. (c) Rotor resistance to wind when not turning. Pigures on left indicate total pressure on two rotors. (Copyright.)