(d) Printed-Circuit Gage . Advantages are low cost of wave 

 gage construction (constructed of printed-circuit board on For- 

 mica grade FF-91, selected because of a low moisture absorption 

 characteristic), good linearity and dynamic response, and neg- 

 ligible obstruction to wave fronts. Disadvantages are the 

 necessity to electroplate the surface of the rod with silver 

 and the difficulty of maintaining clean surfaces during opera- 

 tion. Deposits on the rods cause a shift in the null point of 

 the bridge and a distortion of the calibration curve. 



The above characteristics of wave height measuring assemblies reflect 

 the experience of instrumentation engineering during the period 1952 to 

 1964. Since that time, many improvements have been made in electronic 

 circuits and the use of different materials. Thus, the design of wave 

 gage instruments has changed considerably in recent years; the best 

 method of obtaining up-to-date information concerning the best designs 

 of the instruments is to contact the electronic design and development 

 engineers in the different laboratories that use the devices, such as 

 CERC, WES, Massachusetts Institute of Technology (MIT) , University of 

 Iowa, National Research Council, Ottawa, Canada, and the manufacturers 

 of commercial instriomentation. 



The prototype wave data needed for the basis of model design and 

 operation, and the analysis of test results, are obtained by hindcasting 

 techniques and the direct measurement of the wave heights and periods. 

 CERC has used wave gages since 1948 to obtain prototype wave data. Two 

 basic types of gages are used in the field; the step-resistance staff 

 gage and the underwater pressure-sensitive gage. Three step-resistance 

 gages that have been developed are a series type for use in freshwater, 

 a parallel type for use in saltwater, and a relay type for use in water 

 where wide ranges of salinity occur. The pressure gage can be used in 

 water of any salinity. Details of these gages, including theory of opera- 

 tion, techniques of fabrication, calibration, installation, and mainte- 

 nance, are discussed by Williams (1969). 



(2) Measurement of Wave Forces . Breakwaters and other coastal 

 structures were designed and constructed long before reliable information 

 was available concerning the magnitude and distribution of the forces that 

 occur on the structures due to wave action. However, the tremendous forces 

 exerted on coastal structures by storm wave action was recognized by early 

 designers, as evidenced by descriptions in the literature of damages that 

 occurred and by atterapts to measure the magnitude of the wave forces on 

 structures. According to Gaillard (1904), Thomas Stevenson was the first 

 to measure wave forces in 1842 and continued the measurements for many 

 years. The first wave pressures measured at IVES were for a model study 

 to determine pressures on a vertical-wall breakwater subjected to non- 

 breaking waves (Hudson, 1942) . 



Measurement of the pressures exerted on coastal structures by breaking 

 waves requires pressure transducers with characteristics matched to the 

 characteristics of wave pressure phenomena. The extremely short duration 



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