8 COLLAPSE OF TEXAS TOWER NO. 4 
six-tenths of a nautical mile from where it was thought to be all 
that time; and 
(6) The water depth was actually found to be 185 feet instead 
of the 180 feet as thought at the time of marking the spot by 
buoy. This error could be attributed to either the error in posi- 
tioning as placing it within a deeper fathom line or because of 
bottom sand ripples 5 feet in height, the highest point in roughly 
an acre of coverage being the return received by the echo sound- 
ing equipment. 
Other aspects considered in the feasibility study included the con- 
figuration, or size and shape, of the towers, which would be governed 
in large measure by the prevailing environment of natural forces. 
The aspects of configuration most immediately affected by these en- 
vironmental forces were the height of the platform above mean sea 
level, the number and size of the legs, and braced legs as opposed to 
unbraced legs for a water depth of 185 feet. 
(a) Platform elevation — 
The maximum intensity of a wave force occurs close to the maximum eleva- 
tion of the wave crest. If these large intensities of wave force should be applied 
to large areas such as the platform, excessive total forces would result. There- 
fore, safety and integrity of the platforms requires that the platforms themselves 
always be definitely above the crests of any waves. 
This criterion is confirmed by the loss of two oil-drilling rigs in the 
Gulf of Mexico which succumbed to waves striking the platforms.® 
The Woods Hole Institution also made a study of the weather re- 
ports for the preceding 20 years and found that the maximum wind 
velocity of 128 miles per hour occurred during a hurricane in 1938 and 
that the computed average height of the 10-percent highest waves was 
66 feet which occurred during an easterly storm in November 1945. 
According to theory, the height of one wave in every thousand waves 
will be 114 times higher than the average 10-percent highest waves. 
This theory has been fairly well substantiated for waves up to 20 feet 
in height but not for waves in excess of that height, because of the diffi- 
culty of observing and measuring waves of greater height. However, 
the theory is presumed to hold true for waves of greater heights than 
20 feet. The measurement is from trough to crest which, as a rough 
rule of thumb, means that approximately 60 percent of the wave would 
be above and approximately 40 percent below mean sea level. 
A large and unresolved uncertainty remains concerning the maximum height 
of waves that may strike the platform supports during its useful life. While the 
maximum possible height is uncertain, there seems to be a definite probability 
that one such wave (gigantic) may strike the platform supports within a pe- 
riod of 20 years. Our design has proceeded on the basis that the occurrence of 
one such wave may cause stresses in the structural elements of the platform 
supports into the plastic range of stress for the structural materials. However, 
if the platform itself is not struck by such a wave, the ultimate safety of the 
platform and the personnel on it will not be endangered and it is believed that 
repairs or replacements of overstressed elements can be made if such a wave 
occurs.” 
After conisderable study, it was decided that the probability of 60-foot waves 
occurring several times during a period of 20 years at any of the locations 
definitely exists. * * * Such waves are associated with northeasterly or easterly 
storms rather than with hurricanes and the wind velocities associated with such 
waves are those of storms. * * * Under hurricane conditions with high wind 
5“YDesign and Construction Report on the Texas Towers Offshore Radar Platform,” 
Moran, Proctor, Mueser & Rutledge, September 1959, p. 23. 
6 Ibid., pp. 20, 21. 
