Since investigation revealed that no known instrument had embodied 

 in it all three of these features, it was decided to design and build an 

 appropriate system at the David Taylor Model Basin. After some consid- 

 eration of the imposed conditions, it was decided that a small floating 

 buoy (SPLASHNIK) which measures apparent vertical acceleration and 

 telemeters the information back to the ship could be designed to fulfill 

 the requirements. 



The intent of this paper is to describe the SPLASHNIK system, the 

 data reduction method, some experimental verification of the method, and 

 some proposed improvements. It should be noted that this technique of 

 wave measurement (recording of vertical acceleration) is not new. In 

 fact, one instrument described by Dorrestein-'- is somewhat similar to 

 the SPLASHNIK and has been in operation for several years. Other 

 institutions are also known to be experimenting with accelerometer wave 

 buoys. However, several basic design differences make the SPLASHNIK 

 especially useful as a tool in the study of ship behavior. A drawing 

 of the SPLASHNIK appears in Figure 1. 



OPERATING PRINCIPLES 



The general operation of the complete system of sensing and record- 

 ing is shown in Figure 2. An accelerometer consisting of a mass and a 

 flexible arm is attached to the base of the float unit. Part of the mass 

 is an eddy current damper attached near the outer end of the accelerometer 

 arm. As the float moves up and down on the waves, the displacement of 

 the mass in reference to the base causes a radio transmitter to change 

 frequency. The change in frequency is proportional to the acceleration 

 being experienced by the buoy. The output of the transmitter is fed to 

 an antenna mounted on the wave-height buoy float. The signal transmitted 



■'■References are listed on page 16 



3 



