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é —— oO) Eee THE MARINE RECORD. THE TRANSVERSE STRENGTH OF SHIPS.” Mr. J. Bruhn read portions of his paper on “The Trans- verse Strength of Ships,” which was accompanied with several elaborate tables. He said in a paper read before this institution in 1882 by the late Messrs. Read and Jen- kins, attention was called to the fact that the question of transverse strength of ships had not received the con- sideration it deserved. The remark was perhaps as true now as then. The longitudinal strength has come to be looked upon as the strength of a ship to such an extent that, whenever the calculated strength of a ship is men- tioned, no other is usually thought of. The longitudinal bending moments being so much larger than the transverse ones, it follows that the longitudinal strength is more im- portant than the transverse, but itis so only in regard to the quantity of material used in the construction. From the point of view of the safety of the ship and cargo, the strength of no one part of the structure can claim to be more important than that of other parts. If the cargo or ship is damaged, it matters little whether the cause is longitudinal or transverse weakness. It is, therefore, de- sirable to have a method whereby the transverse strength of a ship can be estimated as exactly as the longitudinal strength, or practically so. The object of his paper was to attempt to provide at least another step towards the es- tablishing of such a method. The distribution of the ma- terial in the longitudinal girder is comparatively simple. The breadth, depth, and form of the girder being practical- ly given, and the strength can only be varied by modifying the thickness of the plating. It is otherwise with the transverse material. Here the efficiency, or the strength, lightness, and compactness of the structural arrangement, depends to a much greater extent on the form and distri- bution of the material. In this case there was much more freedom in the design of the structural parts. It is, there- fore, all the more important to have a method whereby the stresses can be estimated, and as, moreover, the case is somewhat more complicated than that of estimating the longitudinal strength, the chances are that the employment of a scientific method will detect greater room for improve- ments in design in this respect. The transverse stresses were those tending to change the form of the cross sec- tions of the vessel. They were due to transverse forces acting on the ship, and, indirectly, to longitudinal forces. The transverse forces were: (1) she weights of the structure and cargo. (2) The reactions of these weights due to changes in the motion of the vessei (rolling, pitch- ing, or heaving). (3) The externally applied forces, such as the pressure of water, keel blocks, or other supports. The longitudinal forces that affect*the transverse strength of a ship are chiefly those which bend the vessel in a fore and aft plane, and, consequently, tend to deform the transverse sections. For convenience in the examination of the transverse strength of a ship, Mr. Bruhn assumed a section cut out of the vessel, and then applied all those forces to it which are necessary to keep it in equilibrium under the given conditions. This ring must be in equili- brium. The weight of the structure and the cargo, the pressure of the water, and the bending and direct stresses on the ring and the corresponding cargo be equal to the displacement. The vertical main forces are thereby bal- anced. The pressure of water on the two sides of the vessel will of course always be equal in still water. The ring, as a whole, is therefore in equilibrium. If we assume the deck beam removed, then the structure is simply firm, and the stresses are directly determinable by statistical means. When, however, the beam is fitted, then there will be a force and a bending moment which will resist part of the forces, but how large a part cannot be directly de- termined by the ordinary conditions of moments. Messrs. Read and.Jenkins adopted, as the additional requirement necessary for the solution of the problem, the conditions of continuity in the deflexions of the structure, and they determined by these means the forces in the case of vessels esting on keel blocks in dry dock. The most direct method for the solution of a problem f this nature is, however, probably that based on the prin- iple of least work. The systematic application of this inciple to engineering problems is mainly due to Alberto stigliano, of Turin. His methods have been extensively mployed by civil engineers on the continent; but have not, herto, been applied to ship calculations, although ex- -*From an address read before the Institution of Naval Architects at Glasgow, June 25. ceedingly useful, not only in calculations for the strength of the main structure of a ship, but also in the determina- tion of the strength ot many details of the structure, such as rudders, stern forgings, masts, and rigging, etc. The very general character of the method and the possibility of employing the ordinary rules for approximate integration makes it peculiarly applicable to the unsymmetrical struc- ture of a ship. Mr. Bruhn showed that transverse bulk- heads are very important factors in the athwartship strength of ships. Their effect must be trarismitted to the frames and beams through the shell plating, deck plating, and stringers. As regarded the force which is introduced by the heavy blows of waves striking a vessel, it should perhaps be estimated at about .2 of a ton per square foot. It would, obviously, be not so great as the action of a heavy sea upon an immovable mass such as a pier head or sea wall, which would not yield to the influence of the blow. This last was calculated by Mr. J. Stevenson to be 3 to 3% tons per square foot for Atlantic waves striking a vertical wall or rock. Appended to the paper is a table of the calculated stresses on the framing of various vessels. worked out on the author’s basis. Mr. B. Martell said that the great advantage of Mr. Bruhn’s paper consisted of the fact that it was a scientific investigation of a complete nature, tending to practical results, and would therefore enable shipbuilders to follow the investigations and arrive at more certain results in re- gard to the problem under discussion. Dr. more complicated problem than longitudinal strength; and he thought, indeed, it was an interminable problem. The principle of least work leaves it necessary to make some as- sumption; still, he thought that principle was an advance. The author had referred to the support given by transverse bulkheads in resisting stresses. The speaker agreed that the principle element of strength in the transverse form are the transverse bulkheads, so that these afforded not only safety against flooding, but also added to the strength of the ship. He was not disposed to go so far as the author in considering that the bulkheads would relieve the framing almost entirely. Any results obtained by statical calculations in still water was over-ridden by the result of waves upon ships at sea. Mr. J. Foster King referred to that part of the paper in which the author dealt with the bending of the floors. Mr. Bruhn had stated that an examination of the curve and the moments of the structure, cargo and water pressures would show that the horizontal pressure of the water on the sides of the vessel is the most important factor in determin- ing the magnitude of the stresses, because, although the pressure of the water on the bottom is somewhat in ex- cess of that of the weight of the structure and cargo, and the floors might therefore be expected to bend inwards, the pressure on the sides is sufficient to completely re- verse this bending tendency, so that the largest bending moment on the girder is at the center of the floors, and is tending to bend the floors outwards. Mr. King considered this matter required explanation, and referring to a later passage in the author’s paper in which it was stated that the frames may also be supposed to be held rigidly fixed at the lowest complete tier of beams, in particular when the beams are loaded with cargo, and, therefore, tending to bend the frame in a contrary direction to that due to the pressure of the water. Mr. King considered this was the reverse of what would be expected from a practical point of view. He was also of opinion that Mr. Bruhn argued to wrong conclusions when he said racking strains were small in sailing ships because there were few bulkheads. Mathe- matical calculations founded on so many unknowns, which must remain unknown, could not give satisfactory results. Professor Biles said, while deductions from such a papér must be carefully made, he considered that Mr. Bruhn had made a distinct advance into the unknown regions of the strength of vessels. Mr. Bruhn, in his reply, said he had not attempted a complete solution of the problem of the transverse strength of vessels, but had attempted in his paper to give a method for comparative purposes. OO oor Tuk invention of the mariner’s compass by Flavio Gioja is to be celebrated this summer at Ama)fi, Italy. Gioja came from Positano, in the hills back of Amalfi. There have not been wanting those who contend that the invention, like most others, was gradual, and that the tendency of the mag- netized needle to point north was known long before Gioja’s time, it even having been familiar to the Chinese, Elgar said that transverse strength was a much. -score years be $200,000,000., AUGUST I5, 1901. THE THERMOMETER. It is probably not generally known, says Popular Science Monthly, that the thermometer was invented by Galileo. When we remember that we owe to this one man not only the foundations of physical science, but also in large Meas- ure the pendulum, the compass, the telescope and the mi- croscope, it may lead-to a certain amount of modesty in our appreciation of modern inventions. Galileo, probably in 1595, invented the open air ther- moscope. Ferdinand II., of Tuscany, first sealed the glass, making the instrument independent of atmospheric pres-— sure. Many improvements were gradually made, especially in the endeavor to fix points on a definite scale, the freez- ing point of water being first used by Robert Hooke in 16€4. Of the three thermometers still in use, Fahrenheit’s thermometer was invented in 1709, Reaumur’s instrument is 1730, and the scale of Celsius—the centigrade scale—in 1742. None of these thermometers, however, is now used in the form in which it was originally devised. It is a somewhat curious fact that the instrument constructed by the German, Fahrenheit, is used almost exclusively by the English-speaking peoples; that invented by the Frenchman, Reaumur, is used chiefly in the north of Europe, while that of the Swede, Celsius, is used in French-speaking coun- tries. The centigrade scale, the zero point of which is the freezing point of water, is now used nearly universally in scientific investigations. The main objection to its common use is the length of the degree, the interval be- tween the freezing and the boiling point of water being di- vided into 100 instead of 180 degrees, as on the Fahrenheit scale. This makes the length of a centigrade degree nearly twice—nine-fifths—that of the more familiar Fahrenheit degree. —-> oe HOME DEVELOPMENT. To the Editor:—The Martine Recorp is one among the very few papers which has the wisdom to advocate the construction of home ship canals and the development of the great lake region, and render “Uncle Sam” independent of a foreign nation. The construction of the Nicaraugua canal is wholly unnecesary. It would cost nearer. $1,000,- 000,000 than $140,000,000. The Ocha dam and the locks of the canal will cost $140,000,000. The excavation of a harbor on the east terminus of the canal and the break- water on the Pacific coast, the construction of a railroad along the canal and dredging the lake will cost enormously. It is asserted that Lake Nicaragua is subsiding; the rain fall, in some seasons, is only 16 inches, and as the country is subject to volcanic actions, the permanency of the lake is uncertain. The legislator who votes the people’s money for the Nicaragua canal is committing a great mistake; one-fourth the cost of that canal will furnish a deep water way from head of Lake Erie to the Gulf of Mexico, and will accommodate $100,000,000 tonnage which will in a half Yours truly, QUAKER. Ss THE STEAM TOWING MACHINE. The following letter should be of interest to every one connected with water-borne commerce. The fact that the towing machine on the tug Vosberg is No. 0, the smallest size manufactured by the American Ship Windlass Com- pany, makes the value of such a machine more easily com- prehended: SuppEN & CuristENson, LUMBER AND SHIPPING, 6 CALIFORNIA STREET, San Francisco, August 5, Igor. G. M. Josselyn & Co., San Franciso, Cal. Dear Sirs:—Relative to the Providence towing machine recently placed on the tug George R. Vosberg would say that Mr. U. S. Bryant, who is in charge of same, has re- ported to us that he considers the machine an excellent ad- dition to the tug, and that same has, in his estimation, paid for itself in the first trip over the Nehalem in saving the barge which was in tow from destruction on the bar. Immediately on the grounding of the barge the machine paid out cable enough to permit the tug to pass over the bar, and then with the combined power of the tug and tow- ing machine the barge was hauled off the spit. Mr. Bryant states that he considers the tug power in- creased one-third by the use of the machine. Yours very truly, (Signed) Suppen & CuristENSoN.