LENGTH 



27 



crease in the length of the wave continues not only as long as its 

 height is increasing rapidly, but even after it has attained the maxi- 

 mum height to which the particular wind in question can raise it. 



Table 10, abbreviated from one already published, gives at least a 

 rough picture of the average lengths of the waves to be expected 

 out at sea with winds of different strengths. 



Table 10. — Average lengths of waves, observed at sea, according to the strength of the 



wind 



[Adapted from Kriimmel] 



The averages presented in table 10, which were based on a large 

 number of observations made in different regions, show that ocean 

 waves are usually more than 100 feet long from crest to crest, unless 

 the wind is very light. A similar tabulation (table 11), based on 

 other published measurements of waves from 4 to 46 feet high and 

 more than 60 feet long, also shows that storm waves are not ordi- 

 narily longer than 450 to 550 feet in the North Atlantic or North 

 Pacific, and perhaps a little longer, though not averaging so, in high 

 latitudes in the South Atlantic and South Pacific. To find really 

 long storm seas, w r e must turn to the so-called "Southern Ocean," on 

 the route from South Africa to Australia, where the seas are com- 

 monly as much as 600 to 800 feet long in heavy gales. An average of 

 775 feet has, in fact, been recorded there for an entire day, with 

 occational waves 1,200 to 1,300 feet long. 



The lengths just quoted are for waves either still gaining height 

 or at least near the maximum heights to which the wind in ques- 

 tion can be expected to raise them. Old swells may be much longer 

 still. And the North Atlantic yields nothing, in this respect, even 

 to the Southern Ocean. Swells as long as 1,320 feet (calculated from 

 their periods, as explained on page 35) have, for example, been ob- 

 served by French officers in the Bay of Biscay; swells 866 to 1,481 

 feet long on the west coast to Ireland; others averaging 1,850 feet, 

 and with a maximum of 2,594 feet (by similar calculations), on the 

 south coast of England following a severe Atlantic gale; and still 

 others with a length of 1,914 feet off the Cape of Good Hope many 

 years ago. Swells of 2,719 feet, reported for the equatorial Atlantic, 



