8 The Sea 
in almost complete mathematical detail the motions of fluid 
particles in a water wave simply by starting with such funda- 
mental notions as Newton's laws of motion and the principle 
of the indestructibility of matter. However, in cases of turbu- 
lent motion, such as in a breaking wave or surf, ordinary 
methods of mathematical analysis are powerless. As a result 
it is impossible to give tables about breaking waves, or “un- 
dertow.” 
HOW BIG CAN A WAVE GET? 
Landlubbers are often paralyzed with fear at the size of 
ocean waves. Sea stories make a point of describing “moun- 
tainous’ or “towering” seas. During a severe storm at sea, 
ocean waves often do seem gigantic, and it is true that they 
can—and do—inflict terrible damage. However, it is a fact 
that the heights of waves at sea are often exaggerated. Ob- 
served wave heights seldom exceed 40 feet from trough to 
crest. In a severe hurricane, reports have been made of 
waves up to 100 feet high. Such exceptional heights are prob- 
ably due to the sudden piling up, atop one another, of sey- 
eral wave peaks, building up for an instant into one huge 
mountain of water. Waves of this size, fortunately, are rarely 
encountered. | 
A strong wind, blowing for many hours, may build up a 
considerable sea. It is important to remember that the size of 
ocean waves depends not only upon the strength of the wind, 
but also upon the “fetch,” that is, the distance to the wind- 
ward shore. 
WAVES AS AIDS TO NAVIGATION 
After the wind has died down, the swells generally proceed 
in long parallel rows in a very orderly fashion. Their shape is — 
