96 LAUNCHING DATA FOR A BATTLESHIP. 



ence between actual dynamic conditions and the assumed static conditions lessens 

 the tendency to tip, it would increase the lifting moment about the fore poppets and 

 cause the vessel to lift sooner. The obstructions between the camera and the ship 

 prevent a full investigation and measurement of the waterline on the picture record ; 

 it was found, however, that the wave at the stern is followed by a great hollow and 

 great reduction of depth of water over the ways and at the end of the ways, in 

 wake of the middle body of the vessel, when lifting was estimated to take place. 

 The over-run and deferred lifting does not lessen the maximum pressure on the 

 fore poppets when the vessel does lift. On the contrary, if it is caused by a trans- 

 fer of displacement from amidships to the after end, the same lifting moment is 

 reached with a less total displacement, and consequently with somewhat greater 

 pressure on the fore poppets. 



The coefficient of initial friction is a matter of great interest. The observed 

 points near the origin on the distance curve are not sufficiently numerous and ac- 

 curate to allow it to be determined by differentiation. A slight modification of the 

 distance curve, such as would be made in fairing, will cause a great variation in 

 the derived acceleration and coefficient of friction. The initial friction could not 

 be determined from the pressure in the cylinders of the hydraulic triggers, for the 

 reason that they were pumped up to a pressure tending to force the ship up the 

 ways, to be sure that she did not settle on to the dog shores. The pressure in the 

 cylinders was therefore greater than it would have been had the vessel been allowed 

 to settle on to the triggers, and the pressure in the cylinders to regulate itself to 

 the amount necessary to make up what friction lacked to prevent the vessel from 

 starting. 



The different papers on launching describe various types of chronographs for 

 observing the time and distance run, from which the velocity and other functions 

 are found. A photographic method was devised by Naval Constructor E. F. 

 Eggert, U. S. Navy, about 1905, and used very successfully for the Mississippi and 

 the Kansas. Now that moving-picture cameras are available, they offer the readi- 

 est means for obtaining photographic records. Photographic methods have such 

 an advantage where simultaneous observations are required, that arrangements 

 are now in hand to use a moving-picture camera to record the observations and data 

 for tests on ships' auxiliaries, such as training turrets, operating test on boat 

 cranes, etc. It provides for accurate simultaneous records of the time, the position 

 of the moving part, trim of ship, heel of ship, position of controller, and readings 

 of ammeters and voltmeters, as they all appear in each moving-picture, and give 

 the data to calculate the power, velocity and acceleration. The method, in addi- 

 tion to giving accurate records, obtains them in the shortest possible time. 



The arrangement for picture record of the Oklahoma's launch was made 

 to suit the conditions as they existed, and with but limited consideration in ad- 

 vance. Plate 35 has been made up to show a more convenient arrangement. The 

 axis of the camera is pointed normal to the vertical plane containing the scale and 

 is at the level of the center of the scale. The scale is given the same inclination as 



