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April, 1909 TAE Marine REVIEW GerMAN NaAvAL DocKSHIP VULKAN. generated in four Mehlhorn water-tube boilers. One of the purposes for which the vessel is destined is to serve in salvage operations for sunken submarines, the necessity for such a salvage ship hav- ing become more and more apparent as the development of submarine practice has progressed. The trials of the ship have been very satisfactory--so -much sO, in fact; that a second. and: larger ship of the same type 1s under con- sideration for the other great German naval bases. EXPERIMENT IN SHIP DESIGN. At the meeting of the Manchester so- ciety of engineers, held on Saturday, Feb. 26, Mr. Leslie Denny, of Dumbarton, read a paper on the general principles in the design of modern ships. Ton- nage, he said, was somewhat of a mys- tery to those unconnected with ship building and shipowning. Broadly, gross tonnage was the entire internal capacity of the vessel taken in cubic feet and divided by 100, while the net tonnage was that figure less deductions for ma- chinery space, crew space, light and air for machinery, etc. He explained the methods by which data of design were obtained, specially as to weight, capa- city and speed. When dealing with speed and power, he said, especially where a departure had occurred from anything previously done, another fac- tor was introduced, and that was the data got from the experimental tank. In the case of his own firm, this was a canal 300 ft. long, 22 ft. broad, of 2 depth of 10 ft. Over it there was a pair of rails, on which ran a carriage, and attached to this carriage was an accurate model of the ship immersed in the water to her correct designed draught. The truck was driven along by means of electric power at suitable speeds, and by somewhat elaborate cal- culations the resistance of the model was obtained. This resistance was then translated into resistance for the full- sized ship, and by that means a curve was obtained of what was called the effective horsepower, or the horsepower that would be necessary to tow the ship. The difficulty of deciding the power necessary in the ship to drive her at a given speed only began at this point, be- cause it was found that this power necessary was considerably greater than the effective horsepower, sometimes as much as double or even more. Theory alone, unless backed up by ample prac- tical experience, was of very little value in fixing the efficiency. In the case of an exceptionally fast vessel small dif- ferences in propellers often made large differences in the results, and even after the builders had done all they could, they were only perfectly happy in the case of the fast vessels when the first double run on a measured mile con- firmed their calculations. MODIFIED PLANS FOR PEARL HARBOR DRY DOCK. The dry dock at Pearl harbor, Hawaiian islands, was described in the Martne Review of March 25. The navy department, through the 'bureau of yards and docks, has now prepared revised plans and_ specifications for this dock. Proposals for this work were opened Dec. 1 last. but: have been rejected owing to lack of suffi- cient funds, for the construction of a dock 1,200 ft. long as contemplated by the department. A revision of the plans shortening the dock to 620 ft. has therefore been made. All the features of the former design shave been retained excepting that where formerly there were two docks in one, an inner and an outer; with a caisson between them, in the new de- sign there will ibe only the outer dock. The structure will 'be built in such a way that at any future time it may be lengthened by the addition of the inner dock. To accomplish this the side walls of the dock will be built exactly as if the long dock were to be constructed; and a concrete wall will be built across the head end, forming. a closed basin. This .concrete cross wall or head is to 'be STERN VIEW GERMAN NavaL DocKsHIP VULKAN.