3. PROCEDURE 



The study was divided into separate consideration of deep-water 

 and shallow-water waves, with the distinction between wave types 

 made on the basis of the commonly employed criterion cited by 

 Gaillard; deep-water waves are those propagated in depths greater 

 than half the wave length, shallow-water waves are those propagated 

 in depths less than half the wave length. It may be noted that while 

 this division of wave types is arbitrary, it is sufficient for the purpose 

 of this study. 



Twelve deep-water and twenty shallow-water waves, covering the 

 -available range of wave characteristics were studied. 



4. EQUIPMENT AND METHODS 



The wave tank. — The concrete wave tank is 85 by 14 feet with a 

 depth of 4 feet. One side is fitted with six glass windows each 24 by 

 40 inches. Each window has etched scales graduated to hundredths 

 of a foot. 



The . wave generator. — The wave generator is a counter-weighted 

 wooden plunger with the forward face set at 51° with the vertical. It 

 is driven by a variable speed, three horsepower direct current motor. 

 Wave heights are varied by setting eccentrics, adjustable by quarter- 

 inch increments to 7K inches, and plunger connecting arms, adjustable 

 in l)2-inch increments. 



Wave absorber. — A 6-inch layer of ){ to % inch commercial gravel 

 placed at an angle of 12° with the horizontal is constructed in the end 

 of the tank opposite the wave generator to serve as a wave absorber. 

 A screen consisting of one thickness of number 16 screen wire laced 

 to a thickness of )^-inch wire mesh is stretched four inches above and 

 parallel to the top of the gravel slope. A wave absorber of similar 

 design but of greater slope is placed behind the plunger. 



Wave height measurement. — Three sets of point and hook gages 

 were used to determine still water levels and to measure wave heights. 

 A point gage was adjusted to the top of the wave crests and a hook 

 gage to the bottom of the troughs ; the wave height being the distance 

 measured between point and hook. 



Wave length measurement. — Each of two point gages, one fixed 

 and the other movable horizontally, were connected in an electrical 

 circuit with a neon bulb and ground in the tank. The gages were 

 adjusted to just touch the wave crests, the passage of a crest com- 

 pleting the electrical circuit, and causing a short flash of the neon 

 bulb. Adjustment of the movable gage, to secure synchronous 

 flashing of the neon bulbs, indicated that the points were set on a 

 wave length or its multiple. 



408321—41 2 



