HEIGHT 



17 



Table 3. — Probable maximum heights of waves with winds of different strengths, 

 combined from various observations at sea 



[Adapted from Krummel] 



The theoretical relationship between heights of waves and strengths 

 of winds agrees fairly closely with the relationship between wave 

 heights and winds of different velocities, up to 40 miles per hour, that 

 have actually been observed. (See table 3.) But we may point out 

 that the statement, sometimes made, that the heights of storm waves, 

 in feet, average 0.6 to 0.8 of the velocity of the wind, in nautical miles 

 per hour, is not borne out by either tabulation. And the heights of 

 waves, as observed, differ considerably from the theoretical values for 

 stronger winds. Thus the theoretical height of waves for a 56-mile 

 wind is 63 feet, whereas it has been the repeated experience of observers 

 at sea that the upper limit for the average run of waves that accompany 

 winds of 50 to 60 miles per hour, such as are not infrequently en- 

 countered during severe gales, is not more than about 40 feet at most. 

 And waves higher than this are unusual, no matter how high the wind, 

 unless indeed two large waves chance to unite (p. 25) . 



This discrepancy results in part from the fact that the theoretical 

 values, given in tables 4 and 5, are for the highest waves, and these 

 have seldom been actually measured. But the chief reason why waves 

 are seldom as high as should theoretically be possible during severe 

 gales is that winds stronger than 40 to 50 miles per hour seldom blow 

 in a uniform direction far enough for them to produce waves more 

 than 30 to 40 feet high or so. Thus the effective fetch (p. 19) for 

 winter gales in the North Atlantic is not often more than 500 to 600 

 miles, or enough for the waves produced by a 40-mile gale to rise to 

 only about 32 feet, or three-fourths of the height possible with a wind 

 of that strength over an unlimited fetch. And a fetch of even 800 

 miles, such as develops occasionally in the North Atlantic with a pro- 

 longed gale, is no more than is needed for a 50-mile wind to produce 

 50-foot waves. But the effective fetch is longer still in Atlantic gales 

 on rare occasions, as it more often is in the North Pacific, and the 



