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1901.) MARINE REVIEW. 21 ROLLING OF PASSENGER SHIPS AND POSSIBLE REMEDIES. BY LAWRENCE IRWELL. A fact that usually strikes the traveler when crossing the Atlantic is that, in spite of the great and numerous improvements of late years in ocean steamers, which have made life pleasant and luxurious, little has been done to steady a ship when she meets the waves which make her roll from side to side. For a number of years the tendency seemed to be in the direction of increased rolling, for the steadying influence of sails, which makes the motion of a sailing vessel comparatively agreeable, was fast disappearing on large steamers. On the Atlantic liners the sails have been cut down in size until such fragments as remain, when any still exist, are so small compared with the size of the vessel as to retain little power to reduce rolling. Without any unfairness it may be said that until quite recently ship-owning companies did not show much sympathy for the discomfort which rolling causes many passengers. No doubt they became anxious when a ship acquired the unenviable reputation of being an ex-. treme roller, because passengers discriminated against such a vessel, and her earnings diminished as a result; but beyond attempting to deal with abnormal cases, little was done to mitigate the evil. Either rolling was regarded as incurable, or else it was not considered of sufficient impor- tance to warrant a great deal of trouble. Nevertheless, there is nothing that would contribute so directly to the comfort of landsmen at sea, or do so much to. change what is for many persons--men as well as women-- misery into comfort as to minimize as far as possible the rolling proclivi- ties of sea-going passenger ships. The laws which govern rolling are now well understood, and it is scmewhat remarkable that this knowledge has not enabled an effective method of control to be desired. What is perhaps still more remarkable is that the various suggestions for minimizing rolling have not been more systematically investigated. It is not easy to obtain from a ship builder or designer a non-technical account of what causes a ship to roll. The following statement, nevertheless, seems to come tolerably near to an explanation in easily-understood language. A ship rolls about a longitudinal axis which is approximately at her center of gravity, and the rolling is almost at equal intervals and at mod- erate angles in ordinary ships. The heaviest rolling occurs when the wave-period synchronises with the natural period of oscillation of the ship. Quite a large number of ships are comparatively free from rolling till they meet waves of this period, and if such meeting could be avoided, excessive rolling could be prevented. Some vessels have periods as long as fifteen to eighteen seconds for the double oscillation, and as these would require to meet with waves from 1,200 to 1,500 ft. in length in order to provide the conditions of synchronism, it is seldom that they suffer from heavy or cumulative rolling. But waves of the above-named length are not rare on the Atlantic. The limits of heavy rolling are fixed by the resistance offered by the water and air to the transverse rotation of the ship, which is very great because of the large areas that directly oppose motion in a transverse direction. But for this resistance, and the con- dition that rolling is only uniform in time ("isochronous'"' is the technical ' term) within moderate angles of inclination, a few waves of the same period as that of a ship would capsize her. The two most obvious modes of preventing rolling are, therefore, (1) to make the period of rolling of a ship as long as possible, so as to reduce the chances of meeting waves whose period will synchronize with it, and (2) to increase the resistance to rolling. The period of a ship varies directly as her radius of gyration, and inversely as the square root of her metacentric height. Consequently the period may be increased by adding to the moment of inertia of the ship, or by decreasing the meta- centric height. In armored war vessels, the moment of inertia is con- 'siderable, on account of the heavy weights of armor on the sides and heavy guns that are either placed at the side or high up above the center of gravity. Ordinary steamers have not such weights concentrated at considerable distances from the center of gravity, and their moments of inertia are determined by the distribution of material in the hull which is fixed by structural conditions in the hull and by cargo arrangements. Metacentric height, that is the distance of a ship's metacenter above the center of gravity, cannot be reduced below a certain amount, which is necessary to prevent too easy inclination of the ship, or unsteadiness in calm water. All things considered, we may regard the longest periods that the biggest ships are likely to have with advantage to be those named above, fifteen to eighteen seconds. Length of period cannot give immunity against occasional rolling; but the increase of resistance reduces the angles of roll at all times, and especially when the angular velocity is greatest and the rolling is worst, Such resistance is furnished by friction of the bottom of the ship, and especially by projecting parts of the bottom, such as the keel and the large flat surfaces below at the stem and stern. This resistance can be largely increased by means of bilge keels, and their value is admitted by almost all naval officers. The war ships of many countries have been fitted with them for a number of years past with beneficial results, their advantages having been originally proved by careful experiments in the French navy. Further, a number of trials made some thirty years ago on the British man-of-war Greyhound demonstrated that even bilge keels of great size--3 ft. 6 in. deep and 100 ft. in length, on a ship 172 ft. long-- had only an insignificant effect upon speed throughout great differences of trim. A decade ago, bilge keels had not been adopted by the mercantile marine, and there seemed to be an almost universal prejudice against their use among the owners of the great passenger steamers. At this period it would have been difficult to discover any great Atlantic liners that had such keels. Nous avons change tout cela. The St. Louis and St. Paul were fitted with them about fifteen months since; all the more modern Cunarders (eight) have them, and so has the great White Star liner Oceanic. Whenever bilge keels have been made of suitable size and properly placed, it has been found that the angles of rolling have been reduced by nearly one-half. The prejudice against them was due to a belief that they were detrimental to speed. Mr. Frondé's experiments. showed the contrary, but they were, it is true, made in still water. It is certain, however, that at sea any loss of speed which still-water trials might show would be more than compensated for in a heavy sea by gain in speed when the vessel is prevented from rolling through large angles from side to side and undergoing great changes of underwater at every * roll. Experience with ships that have had bilge keels added after running for some time without them shows that there has been no appreciable difference of speed or increase of coal consumption on the subsequent voyages. ; oe Another, and a more drastic method of stopping. or reducing rolling would be to counteract the reclining moment of the ship caused by the ever-changing inclination of the waves by an equal and opposite moment, which would vary as the inclining moment varies. This has been at- tempted at different times and in various ways. It is essential to any de- gree of success, however, that the opposing moment brought into opera- tion should be completely under control, so as always to act in the manner and to the extent required. The efforts to obtain a steady plat- form by freely suspending it and making it independent of the rolling of the ship, have failed--apart from the practical difficulties of carrying out such an arrangement on a large scale--because the point of suspension oscillates when the ship rolls, and the platform acquires a rolling motion of its own. Weights, made of heavy solid material, which move from one side to the other of a ship subject to the action of gravity and rota- tion, fail because they cannot be made to act continuously in the manner required. Some degree of success has been achieved by admitting water into a suitably prepared chamber and leaving it free to move from side to side as the ship rolls. This has been done in several ships of the British navy, but I have not found any record of its employment in the navies of other nations. The movement of the internal water follows the inclination of the ship, but it lags behind, and thus tends to reduce the inclination. Its effect can be regulated by the quantity of water admittea to the chamber and by its depth. The naval committee which experimented with the English ironclad Inflexible 'stated in their report that comparatively slight changes in depth increase or diminish largely the extinctive power of the water. For various reasons--one of which is that while such a chamber is very effective in a moderate sea, it fails in a rough sea when the rolling of the ship is greatest--and perhaps partly on account of the destructive and disturbing effect of 100 tons or more of water rushing from side to side of a ship over 60 ft. wide--these water chambers appear to have gone out of use, and they have been abandoned on the New York and the Paris, which vessels are said to have been supplied with them when-they were first placed on the Atlantic service. A few years ago an Englishman, Mr. Thornycroft, devised a means of checking rolling by moving a weight under strict control from side to side of a vessel so as to continuously balance or subtract from the heeling moment of the wave slope. It consists of a large mass of iron in the form of a quadrant of a circle, which is placed horizontal, with the center on the middle line of the vessel, and there connected with a vertical shaft. This shaft is turned by an hydraulic engine, which is controlled by an automatic arrangement. The heavy iron quadrant is swept around from side to side, revolving about its center to the extent that is required to counteract the heeling movement. Mr. Thornycroft's description. of his apparatus was as follows: 'The manner in which the controlling gear works will be best understood if we imagine a vessel remaining upright among waves, while near the center of gravity of the ship we place a short-period pendulum suspended so as to move with little friction; this will follow the change ini apparent direction of gravity without appre- ciable loss of time, so that any change in the wave angle cannot take place without due warning, which will indicate the time and the amount of the disturbance. It is therefore only necessary to make the motion of the balance bear some particular and constant ratio to the motion of. this short-period pendulum to keep the balance true. The inertia of a heavy. mass will cause some loss of time, as we can only use a limited force for its control; but it is possible to accelerate the phase of motion and over- come this difficulty so as to get good results. If, now, we imagine the ship to roll in still water, the effect of the combination just described will be to balance the ship's stability for a limited angle; but this defect is removed by the introduction of a second pendulum of long period, which tends to move the ballast in the opposite direction to the first one, and enables the apparatus to discriminate between the angular motion of the water and that of the vessel. I find, however, that the long-period pen- dulum is rather a delicate instrument, and that its function can be served by a cataract arranged so as to always slowly return the ballast to the center, and this device has the effect to accelerating the phase of motion which, in some cases, we also require. We are therefore able, by very small parts, to construct an apparatus which will indicate the direction and amount of motion necessary to be given to the ballast at a particular time so as to resist the wave effort; this power of indicating may be con- verted into one of controlling by suitable mechanism. The loss of time due to inertia of the necessary ballast is not always unfavorable when the apparatus has to extinguish rolling motion, the great effect being ob- tained when the ballast crosses the center line of the ship at a time when it is most inclined to the water surface, and this corresponds to a quarter of the phase behind the motion of the short pendulum." This apparatus was tested a few years since upon an-English steam yacht. As far as I have been able to ascertain, however, it has not been tried upon any steamer of very large size, perhaps because a moving weight of something approaching 150 tons would probably be required on such vessels. But, as the power necessary to control the movement of the weight appears to be small, the invention may eventually be used to reduce the rolling of moderate-sized ships, if it cannot be applied to leviathans of the ocean. : That it might be nearer its source of steel supply and also have better freights on its growing eastern trade, the Champion Rivet Co., Cleveland, is planning for new works in the Pittsburg district. A tract of 10 acres of land has been purchased at New Kensington, on the Allegheny river, and the Wellman-Seaver Engineering Co. is preparing details of what it is proposed to make the best equipped rivet-making plant in the world. Its capacity will be considerably larger than that of the Cleveland plant, but both will be kept in operation. The output of Victor boiler rivets, which has been steadily increasing, will thus be much larger than is pos- sible with present facilities. In another part of this issue the Detroit Trust Co., receiver, adver- tises for sale the entire property of the Detroit Boat Works, a concern that for a great number of years conducted on the Detroit river an ex- tensive business in the manufacture of yachts, iaunches, life boats, etc.