14 



A considerable improvement in the compactness of the installation 

 would be obtained if single angular accelerometers were available; development 

 along this line appears worthwhile. However, the combination of two linear 

 accelerometers, as now used, does give satisfactory service although lacking 

 in compactness. If it is necessary to measure heaving acceleration in the 

 vertical plane, the accelerometer must be mounted on a stable platform; the 

 required corrections can, however, be made from a knowledge of the angle of 

 roll. It is felt on the basis of data obtained so far that the errors actu- 

 ally introduced are small, of the order of 10 percent, and that refinements 

 to correct for the effect of roll on heaving acceleration are not worthwhile. 



With regard to the measurement of rolling and pitching angles, it 

 would be desirable to have a small stable element available especially for 

 this purpose with an accuracy of about 1/4 degree in pitch and 1 degree in 

 roll. It should also be mentioned here that a diaphragm pressure gage has 

 been developed at the Taylor Model Basin which will work with this recorder. 



The accelerometer and recorder combination is linear within 5 per- 

 cent from d-c to 1 cps. Lack of calibrating equipment for these low frequen- 

 cies has limited the extent of calibrations. 



One item which may require some additional consideration is the 

 power from which the equipment operates. At present, 110-volt 60-cycle alter- 

 nating current is used. If, in the future, ship's power of 400-cycle a-c be- 

 comes standard, it may be advisable to build the motion recorder and its trans- 

 ducers to operate on the higher -frequency power, which can be done without 

 much difficulty. 



To recapitulate the main points covered here: The recorder and 

 transducers, in their present form, are dependable and sufficiently accurate 

 for the intended service. Proposed additional developments are: 



a. A time and date stamp. 



b. An angular accelerometer (single unit). 



c. A small stable element. 



d. A counter to count automatically the number of cyclic variations 

 that have occurred. 



CONCLUSIONS 



1 . The recorder performs well in the frequency range associated with 

 the rigid-body motions of ships; it provides sufficient attenuation for high- 

 frequency signals. 



