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10 SCOTT'S NEW 1896 F. W. WHE THE MARINE RECORD. ELER & COMPANY. BUILDERS OF ALL KINDS OF COAST PILOT ce SR ts ty EO === — IRON, STEEL AND FOR THE LAKES WOODEN SHIPS; PRICE $1.50. .FOR SALE BY THE MARINE RECORD, WESTERN RESERVE BLDG., CLEVELAND. West Bay City, Mich. F. W. WHEELER, Prest. C. W. STIVER, Secretary & Treasurer. ) IRON WORKS, MARINE ENGINES, DETROIT. MICH. PROM TI] a3 INCORPORATED 1794 ‘Ansurance Company of North America, , CAPITAL, PAID UPIN CASH,. “= C ASSETS, . zi a E CHARLES, PLATT, President. EUGENE L ELLISON, 2d Vice President. GEORGE H. McFADDEN, Vice President. GREVILLE E. FRYER, Sec’y and.Treas. JOHN H. ATWOOD, Assistant Secretary. LAKE MARINE DEPARTMENT, SEORGE J, McCURDY, Manacen MARINE AND INLAND INSURANCE. $3,000,000.00 9,487,673.53 J. D. JONES, Pres, Atlantic Mutual Insurance Co. Organized 1842. Office 51 Wall Street, NEW YORK. Insures against Marine and Inland Transportation Risks and Issues Policies : making Loss Payable in England. Assets over $10,000,000 for the Security or its Policies: The profits of the Company revert to the assured, and are divided annually upon the premiums terminated during the year; thereby reducing the cost of insurance, until ordered to be redeemed, in accordance with the charter, W. H. H,. MOORE, Vice Pres. For such dividends, certificates are issued bearing interest A. A, RAVEN, 2d Vice Pres, J. H,.CHAPMAN, Sec, ON THE STABILITY OF SHIPS.* One of the primary conditions of safety that the de- signer of aship requires to satisfy is that of stability. A ship floating in still water is in the condition, as re- gards stability, of a solid body whose base is a curved ‘surface, resting upon a plane. Such a body will be in equilibrium when its centre of gravity is vertically over “the point of support. The equilibrium will be stable if after a small angular displacement from the position of * rest the vertical through the point of support pass out- “side the center of gravity of the body; and it will be un- stable if after such displacement it pass inside of it. If the vertical through the point of support pass through the centre of gravity of the body after it had been ro- tated from the position of rest, the equilibrium is neu- tral, and the body will remain indifferently in any posi- ‘tion in which it may be placed while this condition is fulfilled. This would be the case of a body with a spherical or a cylindrical base, whose center of gravity coincides with the centre of curvature of the base. ‘The stability of a ship in still water would thus be tested by inclining upon a level plane a solid which has the same curvature as the surface of centres of buoyancy. If a ‘sectional model be made to scale, the lengths of the righting levers, or the horizontal distance of the centre of gravity from the vertical through the point of sup- port can be graphically determined; and this distance, which is the inclining lever, tending to right the vessel when it passes outside the centre of gravity and to over- turn her when it passes inside, multiplied by the total weight of the vessel, gives what is called the amount of stability for the angle at which the length of the lever is measured. levers at successive angles of inclination—say, 10, 20 and 30 degrees, etc.—and setting these up as ordinates of a curve, the abscissa line of which is divided to rep- resent the corresponding anges of inclination, we -ob- tain what is known as a curve of stability. This curve “shows how long the righting moment goes on, increas- ing with the angle of inclination, when it reaches a maximum, and when it finally vanishes and becomes changed into an upsetting moment. The builder does not require to calculate the exact curve of centres of buoyancy, and to follow out in his practical working the *A paper read by Dr. Francis Elgar, F. R.S., M. Inst. C. E., before the British Association, in the Philharmonic Hall, Liverpool, Sep- tember 18, 1896. By measuring the lengths of the righting analogy between that curve and the curved base of a solid resting upon a solid plane. All that is necessary for himis to calculate the positions of the verticals through the centres of buoyancy at successive angles of inclination. This gives the lengths of the rightful levers, and enables the curve of stability to be con- structed. The principal factor in determining a ship’s stability is the distance between the metacentre and her centre of gravity. The position of the metacentre can be de- termined by an easy calculation; but it is necessary to estimate accurately the position of the centre of gravity of a ship and contents in orderto know what stability she willhave. The distance of the centre of gravity below the metacentre requires to be different in ships of different type, according as the curve of stability is large or small for the same metacentre height. In some ships, such as high-sided passenger liners, one foot is ample, because the righting levers go on increasing up toa large angle in this type of ships; but in some ves- sels, such as warships with low freeboards, and heavy weights high up on the sides and deck; three feet and more would be required. It is desirable to give a vessel only the metacentre height that is sufficient for safety and no more, because the less’she has, consistent with safety, the easier she is at sea, and the less will she roll under.the influence of waves. The exact distance be- tween the metacentre and center of gravity that is best for any given ship thus depends upon the type of ship and the vertical distribution of her weights. A ship- builder’s calculations had to be made from the most un- favorable conditions of loading likely to obtain. Continuing, Dr. Elgar said: The third of the pri- mary conditions of safety that a ship constructor has to satisfy isthat of structural strength. It is, unfortu- nately, impossible in the present state of our knowledge of the subject to determine by theory or calculation the exact sizes requisite for the various component parts of the hull; so that empirical rules based upon experience with other vessels and the trained mechanical judgment of the constructor have to be chiefly looked to in the matter. Science has done much in determining the ‘nature of the straining actions set up in a ship afloat, and the laws which regulate them; but it is impossible at present to calculate quantitatively their whole or exact effect upon a ship, and the maximum stresses to which the main portions of the structure will be sub- jected. The most important problem in’practice is that of the stresses to which the various parts of a ship’s hull are subjected when she is crossing waves of about her own length, and is being bent alternately in two oppo- site directions. The most complete calculations yet made of longitudinal straining action among waves— valvable as these are as steps towards an exact solution of the problem and as a guide to the skilled judgment of the constructor—fail in quantitative accuracy, owing to the omission of important dynamical and other con- siderations that have till now defied exact mathemat- icaltreatment. The calculations of the transverse and other. strains of ships among waves fail still more in quantitative value, and it is not yet possible to approxi- mate them with any reasonable degree of accuracy. The sizes of the steel plates and angles required for the hull of a ship of given dimensions are at present regu- lated by empirical rules, or by the judgment of the con- structor. These are corrected from time to time by the results of experience. The data and scientific know- ledge requisite for the purpose are steadily accumula- ting, and may, it is hoped, be sufficient before long to furnish a surer guide to the judgment and a sounder basis of calculation than at present. ee OED FIGURING AHEAD. The competition which the Grummond line has given the Detroit & Cleveland Steam Navigation, Co, this sea- son, appears to have convinced the latter company. that the service between Detroit and Cleveland must be in- creased next season to hold the business. Ata meeting of the stockholders of the Detroit and Cleveland Co. held in Detroit a few days ago, it was decided to inaugurate a double daily service between the two cities next season, and in any event to reduce the price of transportation. It was also settled that in case there was competition, that the D. & C. line would mect any rate offered, and would make a bid for the business equal, if not below that of any competing line. The officials of the D. & C. line recognize the fact that the Grummond Co. has negotiated for a Chicago boat to be put on the line, and they decided that they would -drive the opposition from the field by low rates anda quick service. Assoon as business will warrant next season, the D. & C. Co. will put on a boat leaving each city at9 o’clock in the morning, and another departing at ll o’clock in the evening. ‘Dhey also decided that whether they had opposition or not, the rates of fare and freight charges between the two destinations would be ree as would also’the price of berths for the season ° ; E.T. CARRINGTON,V.-Prest