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e. 'a system of the construction of the vessel 'Making W ONSIDERABLE attention "has been paid within comparatively recent times to. the development of tests upon accurately formed models of full - sized war vessels and ships of the mercantile marine for the purpose of determining in advance the numerous problems con- nected with the movement of the ves- sel, when completed, through the water, and such tests have been so valuable in connection with problems such as speed and horsepower that several of the large ship building firms now make it a standard\ practice to fashion such models of their important vessels from the drawings to an accurate scale and to subject them to actual tests in ex- perimental tanks before proceeding with itself. In addition to this in Great Britain the National Physical Laboratory, belonging to the government, which is situated at Teddington, has an experimental tank completely fitted for such testing pur- poses, and in connection with this we propose briefly to describe the method ef production of the models of vessels in order to insure their absolute ac- curacy with regard to surface and formation presented to the water. Description of the Installation The installation which is to be de- scribed is of an entirely special char- acter, and was constructed by Messrs. W. & T. Avery, Ltd., of Birmingham. A general view of this is illustrated in Fig. 1, while Fig. 2 shows more espe- cially the method of electrically control- ing the movements of the model-shaping 'Fic, 1--Mopet SHow1nc APPARATUS For NATIONAL THE MARINE REVIEW How the Work is Done at the National Physical Laboratory at Teddington. The Models Reproduce With Fidelity the Conditions Which Obtain in Actual Practice. apparatus. Fig. 3 shows in plan and end and side elevation the general ar- rangement of this model-shaping ma- chine. In order to understand the work which this has to do, it is necessary to explain the general process adopted. This consists first of all in melting a large amount of wax in a water-jacketed gal- vanized iron tank, which is also fur- nished with pipes running through it which carry steam from a boiler so that the mass of wax contained in the tank which may be up to 1% tons is uni- formly warmed up to its melting point. Provision is made for the deposition of any impurities contained in the wax by gravity to the bottom of the tank, where they are retained, the pure wax being drawn off at a point a little above the lowest level into a mold. When the wax in the mold is set, it is taken out and the rough model is placed in its upright position so that the top surface corresponding to the deck is brought under the action of an electrically-driven rotary cutter. In this way an absolutely straight and even surface is produced corresponding to the horizontal section taken above waterline through the ship PHYSICAL JTABORATORY March, 1912 ax Models of Vessels at deck level. When this is completed, the model is inverted and is placed on the table of the special machine which forms the subject of these notes. The carriage on which the model is thus placed runs on accurately machined horizontal rails so that it is at all times in perfectly true line as it travels for- ward and backward. Mounted so that they can operate on the wax model, thus drawn backward and forward by. means of a main electric motor and worm drive, are two rotary cutters driven by vertical motors and the crosswise mo- tion of these cutters relative to the table is regulated by gear so that it is at all times proportional to the motion of a pointer on a separate table carrving drawings which will shortly be described. Shaping the Model It will, therefore, be seen that these rotary cutters will take out the surplus wax at any predetermined height on the model to a greater or less degree at any point in the longitudinal travel of the model, corresponding to the position oi the pointer on the auxiliary table carry- ing the drawing. This auxiliary table is also mounted on rails and by means of standards is placed at a suitable height for the operator to work comfortably, and on the table is placed a drawing giving the various waterlines to which the model is to be shaped. The auxili- ary table is driven from the main drive by a change gear so arranged that its longitudinal travel can bear the same ratio to the travel of the main table that the scale of the drawing is to the scale which is required for the wax model and similarly the same ratio is given to the motion of the pointer with relation to the transverse motion of the rotary cutters. In this way by follow- ing any one of the waterlines on the drawing by means of the pointer, the cutters will gouge out a corresponding curve in the wax model and this process is repeated at varying heights of the wax for all the waterlines on the drawing so that the model is shaped into a series of ridges or steps accurate- ly corresponding to the lines of the ship at all points. By shaving all the ridges down to a: smooth surface, it will be seen that an absolute reproduction of the ship's surface to any required scale is produced. When the model is thus finished, it is carefully weighed by means of a special weighing machine which is so accurately adjusted that, although it can record up to a total weight of 2,500 lbs., it can also register a variation of: weight of one-tenth of a pound. After the model is finished in this