20 



WAVE DIMENSIONS 



but refers to the extent of ocean over which the wind has been blowing 

 in a comparatively uniform direction, strongly enough to have pro- 

 duced the waves in question. 



Table 7. — Maximum wave heights theoretically possible with various wind strengths, 

 and the fetches and durations required to produce waves 75 percent as high as the 

 maximum with each wind velocity 



The proverbial rapidity with which the waves rise when a violent 

 squall strikes is not a guide to the rate at which the heights of the 

 waves in question have actually increased, because the squall may have 

 been acting on them for many hours during its advance before reaching 

 the observer. Such no doubt was the case in one recorded instance in 

 the North Atlantic on the 22d of December 1906, when a violent squall, 

 lasting only 4 minutes, resulted in an apparent increase of 7 feet in 

 the height of the waves (Cornish, 1934, p. 9.) ; and in a second, off 

 Cape Horn on the 23d of January 1926, when an increase in the 

 strength of the wind from four on the Beaufort Scale (23 miles per 

 hour) to about nine (56 miles per hour) between early morning and 

 midafternoon, was accompanied by an increase in the heights of the 

 largest waves from about 2 or 3 feet to about 26 feet. 1 



Waves generated by storms have risen close to their maximum 

 heights by the time they have travelled 600 to 700 miles from the place 

 where they were generated. And a fetch of 900 miles probably is 

 sufficient for the development of the largest of storm waves that have 

 been reliably reported anywhere, no matter how strong the wind. 



Thus the waves may be nearly 30 feet high during the most severe 

 blows in the Gulf of Lyons on the south coast of France, where the 

 fetch is only about 400 nautical miles; 29 to 30-foot waves, and higher, 

 have been recorded south of Newfoundland, where the fetch (upwind) 

 was about 600 miles; and 40-foot waves in a heavy swell in the north- 

 eastern Atlantic, west of Ireland, where the distance upwind was about 

 1,100 sea miles to Greenland, or about 1,200 sea miles to the Newfound- 

 land Banks, though the effective fetch may not have been as long 

 as this. 



Observations made many years ago on the west coast of Scotland, 

 where the contour of the coast with its off-lying islands makes it fea- 



' Schumacher, Arnold. 

 Atlantischen Expedition. 



1928. Die stereogrammetrisctae wellenaufnahmen der Deutschen 

 Z. Ges. erdk. ergiinz. vol. 3, pp. 117-119, figs. 52, 54. 



