regularly in order to maintain linearity in their recording. The wave 
heights thus measured were recorded on paper tape by means of a Brush 
recorder, The heights of ten waves for each eccentric setting were read 
directly from the recording paper, averaged, and converted to prototype 
heights. (For convenience, prototype dimensions are used throughout this 
report.) Whenever it was noted that reflection would distort the dimen-' 
sions of the recorded waves, less than ten waves (but no less than five) 
were taken as being more truly representative. 
In order to determine the effect of the offshore structure on the 
waves transmitted over it, the wave gage was moved from its initial loca- 
tion on the centerline of the offshore structure, without the structure in 
place, to a point slightly more than one wave length shoreward from the 
structure in place. The depth of the bottom profile at this point was the 
same as that at the offshore breakwater location so that any noted changes 
in wave characteristics could be directly attributed to the presence of 
the structure. This location was approximately 195 feet (prototype) shore- 
ward of the breakwater. As both the rubble-mound and vertical-face types 
of breakwater fitted quite snugly against the sides of the wave tank, the 
leakage of water at effective velocities around the barrier was very small; 
hence this factor is considered negligible as a source of error in the test 
series, 
Figure 3 shows the results of the wave height measurements made 195 
feet shoreward of the offshore breakwater, without a shore structure in 
the model. The full heavy line at 45-degree slope on the graph in Figure 
3, of course, represents the line of f effect; i.e., in the zone above or 
to the left of this line, the offshore breakwater had no effect relative 
to the dissipation of wave energy. The data points, connected by the 
dashed curved line in Figure 4 represent actual measurements of wave 
heights at the intersection of the bottom profile of the model with mean 
sea level, the measurements taken relative to the undisturbed incident 
wave height, with neither the shore structure nor the offshore breakwater 
in place. Other curves in Figure 4 show the measured wave heights, rela- 
tive to the undisturbed incident wave height taken for each of four con- 
ditions for the offshore breakwater in place. Although reflection at this 
point was considered negligible due to the presence of an effective ab- 
sopber beach landward from the intersection of the bottom profile with the 
test water level (15 feet above mean sea level), it is quite possible that 
some slight amount of reflection from the bottom slope was responsible for 
the crossing of the curves in Figure 4. 
The main results of the study are shown in Figures 3 and 4. Figure 3 
shows the wave height in the protected area immediately shoreward of the 
proposed offshore tripper which wotild be observed for various incident 
wave heights and structure conditions. For example, for a water level of 
+15 feet MSL, an incident 10-foot wave would be reduced to approximately 
a 9-foot wave just shoreward of the tripper if the crest of the wave 
tripper is at +2 feet MSL; and to a 7.6-foot wave if the crest of the off- 
shore tripper is at +6 feet above MSL. It may be noted that essentially 
56 
