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348 isfactory smoothing instruments., The models are carefully painted inside and out, and a standard varnish finally applied to the outside. Before being taken to the basin, the models are carefully measured by the apparatus. From the results of measurement an- other plan is drawn and compared sufficiently with the original lines, to insure that the model accurately rep- resents the ship. All calculations at the model basin are made from the actual lines of the models. All Trials by Weight Adl trials .aré fan primarily. by weight, draught being used only as a rough check. Before beginning a trial, a model is suspended to one of the cranes shown on the carriage, and weighed. It is then ballasted until its weight in fresh water corresponds to the desired displacement of the ship represented. After a trial the. model is check-weighed again when the bal- last has been removed.* In making the tests for speed and other data needed by the engineer a dynamo- meter is attached to the carriage, which runs to and fro on rails above the water. : The model has vertical plates at- tached to it in the center line at each end, which play with very little free- dom between pointers: rigidly attached to the carriage. The result is that with practically no friction the model is constrained to move in the same direction as the carriage and without deviation, while at the same time it is petiectly free to rise and fall, .or change trim. The towing rod takes the resistance of the model, the fore and aft motion of the model, relative to the carriage, is very little. The speed recording drum is ar- ranged to have sheets of paper, about 16 in. by 22 in. secured to it some- what as paper is secured to an ordi- nary indicator drum. The drum is mounted upon a shaft running from end to end, which ordinarily can be turned by hand by means of a wheel. Mounted loosely upon this shaft is a worm wheel, which is connected to the main driving shaft, revolving with the wheels of the carriage. An electric clutch seizes or releases the worm wheel by throwing its current on and off, so that when desired, the drum can be thrown into gear and driven at a speed proportional to the speed of advance of the carriage. Pencils moved by magnets record upon the drum. time and distance. The time pencil is connected with the break circuit chronometer and notes down every second upon the drum. The distance pencil records contacts with pins spaced along the track 30.4 ft. apart. This distance of 30.4 ft. is 1/200 of a knot, a knot being taken THE MARINE REVIEW as 6,080 ft. The length of record corresponding to 10 seconds of time is measured on a special scale, which gives at once the speed in knots. Paper with metallic surface is used upon the drum, and the "pencils" are pieces of brass wire. In the dynamometer proper, the spring is connected at its rear end to the swinging cross-head, which is sus- pended by a rod, about 4 ft. long, and so arranged as to swing very freely. A pin runs through this cross-head, over which the towing rod jaws fit loosely. The cross-head moves in the guide, rigidly bolted to the fixed brack- et. Its travel is about 34 in. between positive stops. At the extreme end of the rod, jtist below the cross-head, are electric contacts adjustable and usual- ly set so that they are made on either side just before the cross-head reaches the positive stop, which is also ad- justable. The forward end of the spring is attached to a screw, which is again secured to the lower end of the trav- eling bracket. Attached to this trav- eling bracket is the arm carrying the record pencil, which then marks upon the drum the exact position of the traveling bracket, and thus determines the position of the forward end of the spring, The rear end of the saddle is fitted with horizontal and vertical knife edges engaging horizontal and vertical surfaces on a pin attached to the lower arm of a bell crank lever. This is balanced upon knife edges and carries by means of the scale beam a stale plan. it. is also..attached a0 the auxiliary beam, which is connected by double pivots to the pointer, which records upon the drum the position of fhe rear end of the spring. The dic tance up from the knife edge center to the line of action of the pointer being 5 ft. 6 in. while the distance down to the line of action of the spring is 2 ft. it will be seen that the motion of the pointer exaggerates the motion of the rear end of the spring in the ration of 2.75 to 1. Adjusting the Apparatus The process of adjusting the ap- paratus is as follows: Before putting in the spring, by means of the balance weights upon the bell crank, the cross-head is brought: to its central position, and care is taken that the cross-head swings in this position whether the pin securing scale pan rigidly to the scale beam is in or out. The position of the auxiliary pointer is then noted. There are fitted to mark upon the drum, when desired, a number of fixed pencils, such as which can be set to record at any position. One of these. called the auxiliary zero pencil, is set so as to indicate always the position October, 1913 of the auxiliary pointer when the cross-head is central and everything balanced. Next a spring is slipped into place and a corresponding back weight. The record pencil is then brought to a convenient position for zero of the main scale, and a scale pencil set to mark this zero. By adjusting the screw forward or back, as may be required, the auxiliary 'pointer is brought back to its zero. When this is the case, the back weight gives the spring a certain initial tension by means of the saddle and cross-head, while at the same time the cross-head is swinging freely in exactly its na- tural or zero position. The scale pan is allowed to swing freely, and a weight of 10 lbs. placed upon it. This extends the spring until the cross- head brings up against the positive stop. The bracket is then screwed forward by throwing the motor in gear until the auxiliary pointer again comes to zero. A scale pencil is set to mark the position of the recording pencil. Twenty lbs. is now placed upon the scale pan and equilibrium again restored by screwing the trav- eling bracket forward. The scale pen- cils such as now record upon the card lines, which correspond to extensions of the spring, measuring 10, 20, 30 and 40 lbs. The weights are removed, . the recording pencil returned to about its zero position, the scale pan clamped in its zero position and the work of adjustment and calibration, which is done more rapidly than described, is complete. Starting with Lower Speeds The model is then attached by the towing rod, which transmits to the spring only the horizontal pull upon it, the resistance of the model being all in a horizontal plane. It is cus- tomary to start a series of runs with the lower speeds and work up by de- grees to the highest speeds, plotting roughly the results as they are ob- tained after each run. In this way, knowing the speed of a run about to be. made, the approximate correspond- ing resistance can be calculated ac- curately--and it is the practice to set the record pencil approximately at this position before making the run, so that the automatic appliance may be called upon -to traverse it as short a distance as possible. These tests are to obtain accurate data as to the vessel which is to be placed in service; to show the least pull or resistance at the desired maxi- mum speed. The actual speed of the model is in a mathematical ratio of the telation between this miniature and the full-sized ship. After a model of satisfactory form has been developed and tested, then comes the further sigs a aa eat oad Fs aan eR d epee at