3 



utilizing a set of linear accelerometers . Signals proportional to the rolling 

 and pitching angles may be obtained from gyroscopic stable elements. It is 

 necessary that the stable element have a long natural period as compared with 

 the periods of the motions to be measured. 



It was decided that a device should be developed which would measure 

 and record the heaving, rolling, and pitching accelerations of a ship and, in 

 addition, have two spare channels available which could be utilized for record- 

 ing the rolling and pitching angles or, alternatively, some other quantity 

 such as strain. To reduce the cost, standard components were used as much as 

 possible, and refinements in the prototype model which were not needed for an 

 effective evaluation of the suitability of the basic apparatus were omitted. 



Since analysis of records is a laborious and time-consuming opera- 

 tion, the apparatus was designed to be used as a sampling device, that is, to 

 record the data only for a relatively short duration at preselected intervals 

 of time. Thought was also given to providing means which would cause a record 

 to be made only when the value of the measured quantity exceeded a preselected 

 magnitude. However, this was considered to be one of the unessential 

 refinements . 



Inasmuch as the equipment was intended to operate aboard ship over 

 long periods of time, including storm periods, it was felt desirable to re- 

 quire that the apparatus operate from power normally available on most ships 

 at the voltage regulation of such power sources. Furthermore, the instruments 

 and the recorder had to operate satisfactorily under the environmental con- 

 ditions aboard ship at all time. 



Appendix 1 will give the specifications that were established in 

 view of the considerations just discussed. The recorder and the accelerom- 

 eters which are at present used with it, have been developed at the Schaevitz 

 Engineering Company, Camden, New Jersey, in accordance with specifications 

 drawn up by the David Taylor Model Basin. 



THE RECORDER 



The recorder is essentially a direct-recording oscillograph which 

 has provision for automatic sampling and which is designed to operate continu- 

 ously for weeks on shipboard without human attention. The unit is shown in 

 Figures 1 through 6. Its over-all size is 19 3A inches wide, 15 3/8 inches 

 high, and 15 V+ inches deep. All necessary amplifiers, servo-motors, etc., 

 are contained in the case. The only external connections to be made are those 

 to the transducers (pickups) and to a 60-cycle 110-volt a-c power source. The 

 recorder has a frequency response which is flat within 5 percent from d-c to 

 1 cycle per second. Higher frequency signals are attenuated. 



