To date there is but little organized information available on the 

 actual rolling and pitching angles of ships and even less is known about the 

 bodily acceleration of ships. It is the function of this recorder to provide 

 such information without requiring personnel for the operation of the equip- 

 ment. The present model of the TMB automatic ship's motion recorder was in- 

 stalled on a Coast Guard weather ship during a 2 -month tour of duty in the 

 North Atlantic in the spring of 1951- The recorder and pickups operated con- 

 tinuously during this time and gave satisfactory service. 



This report will give some background leading to the development of 

 the apparatus; the recorder and the pickup devices will be discussed and rec- 

 ommendation for further development will be made. 



BACKGROUND AND GENERAL DESIGN CONSIDERATIONS 



The lack of information on the motions of ships at sea is due pri- 

 marily to the physical and financial difficulties that have been present in 

 attempts to obtain such full-scale data. The cost involved in providing in- 

 strumentation and personnel, with use of the ordinary methods of recording 

 data, prohibits such trips except on rare occasions; therefore such methods 

 cannot provide a sufficiently broad basis from which mean and probable peak 

 values can be determined for given ships operating in the various seas. 



It was considered, therefore, that much profit might be derived from 

 the development of some automatic device which would record the desired quan- 

 tities over long periods of time and which could be installed aboard a ship 

 and left there unattended, except for the purpose of removing the data at in- 

 tervals of several weeks or months. Obviously the .apparatus would need to be 

 rugged and, if it is to be utilized on a large scale, inexpensive. 



Quantities that enter directly into structural design are the accel- 

 erations associated with the rigid-body motions of the ship as well as the 

 angular position of the ship in the gravity field. These accelerations vary 

 relatively slowly with time and their magnitude is generally less than the ac- 

 celeration of gravity. Throughout a ship there are usually high-frequency 

 local vibrations present, which are undesirable for our purpose since they 

 give rise to accelerations of the same or greater magnitude than those due to 

 the rigid-body motions of the ship. It is necessary that measurements be kept 

 free of these higher -frequency components so as not to obscure the desired 

 information. 



The measurement of angular acceleration involves considerable diffi- 

 culty. There dees not appear to be a suitable instrument available which will 

 measure the required rather low values of. angular shipboard acceleration with 

 sufficient accuracy. A measurement of angular acceleration may be obtained by 



