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MARINE REVIEW. Wor. Valls CLEVELAND, ©., ann CHICAGO, ILL] AUG. 17.1500) No.7 EXPERIMENTAL TANKS. Their Advantages in the Progress of Ship Building in Other Countries--Benefits that Might be Derived in the United States. Repeated efforts have been made by the navy department to secure from Congress an appropriation for a tank for experiments with models of ships, with a view to at least keeping pace with other countries in study of the ques- tion of resistance and speed, but as in many other matters pertaining to ship building, these efforts have failed, on account of a lack of a proper under- standing of the benefits that would result from progress in this industry. With a view to calling attention to the great advantages that would be derived from an experimental tank in this country, there is printed on this page an en- graving of the tank of Messrs. William Denny & Brothers, of Dumbarton, Scotland, which was taken froma picture in the exhibit of that company at the World's Columbian Exposition. The description of the tank and its operations was furnished by the famous scientific builders themselves, and can be relied upon as entirely accurate. One great draw-back in connection with PDH Pn a -- Be -- 4 s -- Saale ey KS eee Be, THE DENNY EXPE the few tanks of this kind so far built throughout the world, is the manner in which the great mass of information obtained from them is buried as regards the distribution of scientific knowledge. Should the efforts of the navy be successful, there is no doubt that the builders of merchant vessels in the Uni- ted States would be permitted to share the benefits, but it would seem, in con- sideration of the cost, which would be very light in comparison with the end in view, that the aim here should be to secure the construction of an experi- mental tank under conditions that would serve all interests, and that would bring about a distribution of the knowledge obtained from experiments with the hundreds of different models that might be considered. Many investigators from the earliest times down to the present day, have studied the question cf resistance and speed of ships, and have endeavored to find the " form of least resistance,' but until the late Dr. Froude commenced his investigations at Torquay in 1872, no one had been able to show, ina practical manner, the great value of experiments with models, and to predict with absolute certainty what horse power would be required to propel a ship of given design through the water at any speed. All this Dr. Froude was able to accomplish, and to demonstrate to the satisfaction of naval architects mei %. and engineers, in the numerous papers read by him before various institutions. For many years Dr. Froude carried on his investigations and did a lot of use- ful work for the British admiralty by testing war ship designs, and the ad- miralty has been so impressed with the value of the data obtainable from an experimental tank, that they have erected a splendid tank of their own at Gosport, which is under the superintendence of R. E. Froude, a son, and worthy successor of the late Dr. Froude. Froude's method was adopted by the late Dr. Tideman of Amsterdam comparatively early, but up to the present Messrs. Wm. Denny & Brothers isthe. only private ship building firm in the world which has adopted the method. They constructed their tank as early as 1882, and made the first experiment in February, 1883, so that they have been accumulating valuable data for the last ten years, and stand in an exceptional position among ship builders and en- gineers, for it is perhaps not too much to say, that they are bound to be the best advisers in all matters relating to form and speed. They have made 40,- 000 experiments in their tank with 300 different forms of model, and when it is remembered that each experiment represents a double run of a ship on the measured mile, it can readily be imagined what a tremendous store of infor- mation they have as compared with other ship builders. As a sign of the times i AW ---- uy WY sd ite inond/ei os pyicate Sari, mC & . Rge. Wied mie > RIMENTAT TANK. it may be noted that the Italian government have built an experimental tank at Spezzia, and the Russian government have almost completed one at St. Petersburg, and there are rumors of others to be built in other countries. Messrs. Denny's tank is 300 feet long, 22 feet broad, and has 10 feet depth of water (being rather larger than Dr. Froude's tank, and smaller than the admiralty tank.) It was a happy thought of the late Dr. Froude's when the idea came to him to use parafine wax for his ship models, for it has many advantages over any other material. First, the models can be quickly made and tried. Messrs. Denny's staff can make and try a model in three days. Second, parafine wax does not absorb water, therefore the weight of the models remain constant. Third, modification in form can be easily made. Fourth, no material is wasted, for when a model is finished with, it is melted down for another, even the shavings and scrapings being gathered and melted down. The wax is melted over steam coils and run into a roughly prepared clay mould containing a " cove," so as to cast the model hollow. When cold, the casting is placed on the bed of a shaping machine, which is so designed that the operator can, by working two handles, cause a "' tracer"' to trace out any line on a drawing which may be attached to the machine, and this causes