Table 7 (Concluded) 



Return Per 



iod 





Significant 



years 





Extremal Type I (Continue 



Wave Height, m 







d) 



50 







12.17 



60 







12.35 



100 





Weibull, C = 2.0 



12.84 



5 







9.86 



10 







10.37 



20 







10.84 



40 







11.26 



50 







11.39 



60 







11.50 



100 







11.78 



13. The concept that we refer to as "return period" has been shown to 

 be prone to misinterpretation (Borgman 1963). The statement "50-year wave" 

 may be taken to mean that waves of magnitude greater than or equal to the 

 50-year value occur on the average of once every 50 years. The phrase "on the 

 average" is the key to interpreting this concept. As was seen in the discus- 

 sion of nonencounter probabilities, the chance of encountering a 50-year wave 

 in any given 50-year interval is about 63 percent. The nonencounter probabil- 

 ities given in Table 8 are defined to be the probabilities for any given de- 

 sign life L that an R year wave is not encountered. These values can be 

 used to give further meaning to the return periods and associated significant 

 wave heights reported in Table 6. 



Table 8 

 Estimated Nonencounter Probabilities 





for the 



Extremal 



Type I 1 



Model 

















Design Life, 





Return 



Period, 



years (R) 





years (L) 



20 



40 



50 



60 



100 



20 



0.37 



0.61 



0.67 



0.72 



0.82 



40 



0.14 



0.37 



0.45 



0.51 



0.67 



50 



0.08 



0.29 



0.37 



0.43 



0.61 



60 



0.05 



0.22 



0.30 



0.37 



0.55 



100 



0.01 



0.08 



0.14 



0.19 



0.37 



16 



