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ie UNSOLVED: PROBLEMS IN THE DESIGN AND PROPULSION OF SHIPS. : To Dr. Francis Elgar fell the honor of delivering the James Forrest lec- ture, which formed a fitting prelude to the Engineering Conference ar- ranged by the Institution of Civil En- gineers, which opened on June 19 in London. The subject of the lecture "was "Unsolved Problems in the De- sign and Propulsion of Ships." The class of problems that de- -manded attention first were, said Dr. Elgar, those which bore the most directly upon' safety. at sea. These -were very general and comprehensive in character, and were impossible of anything like complete solution from the purely scientific side; But they were Of vital importance, and _ solu- tions. of them, which were, at any rate, upon the right side, had got to be found somehow for every ship that is built. The. lecturer proceeded. to review the attempts to deal with the load-line problem, remarking that the close attention paid during recent years to the protection of openings in the weather deck, in association with the strict limitation of loading now enforced by the Board of Trade freeboard tables, had resulted in an extraordinary diminution of losses at sea. The great reduction had been in steamers. However empirical and tentative .the procedure may neces- sarily have been, the result was a very large and gratifying saving of life and property. As regards divi- sion of the hull into separate water- tight compartments, even now full compliance with the Bulkhead Com- mittee's rules was by no means gen- eral even in the highest class of steamers. ; STABILITY AND STOWAGE, Nothing could make a ship safe if her stability was not secured by prop- er stowage, but when vessels would obviously admit of being loaded with homogeneous cargoes, so as to have their stability dangerously reduced at sea, the official bodies who assigned loadlines should look for proof that the danger was understood, and that measures would be taken, in regulat- ing the stowage, properly to guard against it. He understood that this was the course taken by the board of trade, and the authorities who as- signed freeboards when cases of such a nature came before them. STRUCTURAL STRENGTH. There was no more intricate or difficult subject than structural strength, the usual calculations being unreliable in practice for the reason that they were generally based upon THe Marine REVIEW still water conditions. It was not known how nearly the results ob- tained by calculation upon assump- tions that differed so widely from the real circumstances corresponded with" the maximum stresses really brought to bear at sea, but it was certain that they were often in excess of the truth. In the new big Cunarders-- Lusitania and Mauretania--the limit- ing stress accepted by Lloyds as de- termined by calculation was 10 tons per square inch, supposing the 'ma- terial to be mild steel whose ultimate tensile strength was 28 to 32 tons per square inch. This gave an ap- parent factor of safety of only three. Many vessels had been running for years in which the figures obtained by calculation for the maximum stresses would amount to 10 tons per square inch. That must be largely in excess of the truth, and it was im- possible to say exactly by how much. CHANGES IN DESIGN. Sir W. White came to the conclu- sion which he (Dr. Elgar) believed was right, that after making full al- lowance for features of modern de- signs that involved additional weight, which the Great Eastern did not pos- sess, her structure was lighter than that of. the corresponding ship of to- day, although the latter was built of steel 50 per cent stronger than the iron plates of the Great Eastern, and the riveting of the edges and butts of plating was much more extensive and efficient, and was performed by hydraulic power where 'strength is most required. The difference in prin- ciple between the two designs was so great, and the comparison of the weights of material they required was So. uch in favor..of the . Great Eastern that there certainly seemed to be a case for inquiry, and for con- sidering the question of a. radical change in the structural design of large ocean liners. Some such change was being introduced into the design of cargo steamers in order to obtain large open holds and facilitate stow- age. These were now being built of large size and depth, with only a sin- gle-plated deck at the top, and there seemed to be no 'reason why this principle should not be applied, to some extent at any rate, to large pas- senger vessels. Any saving of weight thus effected would not only be a saving of cost but would better en- able the difficulties of draught of water in harbor and docks for the largest ships to be overcome. TANK EXPERIMENTS, In order to exhaust the. problem of the best form of ship to meet the requirements of any particular trade or service, 'considerable investigation was required. It could only be made satisfactorily with models in an ex- perimental tank upon 'the late Mr. Froude's system. Dimensions and draught of water were usually' fixed beforehand by commercial considera- tions, and by harbor and dock facili- ties, at any rate within somewhat nar- row limits, and the designer required to test models of varying degrees of fineness im order to determine the point at which the limit was reached beyond which the further increase of engine power and consumption neces-. sitated by fuller lines would be un- profitable. This could 'be determined perfectly in an experimental tank. But that method was unfortunately impracticable for ship designers' in general, because there was no tank in this country available for such purposes. The very few that existed belong either to the Admiralty or to 'private ship builders, and were con- fined exclusively to the work of their respective owners. He had had ex- periments made a few times for him- self, but had to go abroad for the purpose. The tank experiments. re- quired by Mr. Yarrow for his valu- able investigations into the effect of shallow water upon speed were made in the North German Lloyd tank at Bremerhaven, where. other experiments had also been made for him. A Bri- tish ship builder could only get such experiments made by setting up an experimental establishment for him- self, or going abroad. An attempt had recently been made to provide an experimental tank at the National Physical Laboratory, to be worked by members of the staff there, at which ship models might be tested for. re- sistance, but up to now it had been without result. The best practical solution of the long-vexed problem of speed appeared to be an extension of Mr. Froude's system to vessels of the fast liner type, and others with which the ship designer ordinarily had to deal, leaving those of abnor- mal proportions or form, and freaks, and also the work of general research, to a public experimental tank--if ever we found enterprise enough among those interested to set one up in this country. ' PROPELLER EFFICIENCY. Several endeavors had been made to construct a theory for the action of the screw propeller, but designers were bound to fall back upon the ex- perimental method. The difficulty in connection with screw propellers had been greatest in the case of turbine vessels, where the shafts necessarily ran at much higher revolutions than