mum installation on the ship. In particular there shall be no re- 

 quirement for ship drydock availability to install the gear. It is 

 highly desirable that the instrument be capable of being moved from 

 one ship to another with a mini:num of effort. 



e. In high waves considerable spray is to be expected. The in- 

 strument is to be so designed to withstand and minimize the effect 

 of the spray. The instrument should be able to withstand total im- 

 mersion. 



f. Amplitude: The instrument is to be capable of measuring the 

 relative displacement of the sea surface from mean sea level with an 

 allowable error of not more than *5%. It must be able to do this 

 continuously with minimum phase lag and small time constant. 



g. Wave Height Range : The instrument must be able to sense 

 displacements from mean sea level of ±20 feet, giving a total wave 

 height of 40 feet. Resolution should be such that wave heights of 1 / 2 

 foot or greater will be measured. 



h. Period -Length: The instrumient should be capable of sensing 

 all variations in relative sea surface height which have periods be- 

 tween 2 and 25 seconds. In terms of lengths, waves of from 20 to 

 2, 500 feet should be sensed by the instrument. Should the sensor use 

 as its operating principle one which averages readings over a small 

 area of sea surface, the area involved should be less than 5 feet in 

 diameter . 



i. Duration: The instrument should be capable of measuring the 

 relative height of the sea surface as a continuing function of time. 

 Although measurements of 1/2 hour duration will be required ordin- 

 arily, special problems will require records of many hours duration. 



j. Recording and Analysis : 



(1) Visible: A visible, strip chart record of wave height, as 

 function of time, is required. This recording should be normalized, 

 and should be of such a scale as to permit manual digitizing to the 

 accuracy of the instrument at 1/2 second intervals. 



(2) In addition to visual recording, the wave data must be 

 amenable to spectrum analysis on board ship. 



(3) Electric or electronic sensor signals must be such as to 

 permit the Master Shipboard Data Logging and Processing System 



364 



