Chapter 2- The Diving Environment The Diving Environment 35 Water waves develop under the influence of newly formed winds (figure 2-3). The air pressure changes on the surface of the water and the frictional drag of the air develops ripples on the surface. These ripples evolve into waves which increase in size with the wind velocity, duration, and fetch. Fetch is the distance the wind blows over the water. Energy is transferred directly from the air to the water. Waves pushed by the wind will continue to grow until the wind subsides, or until their steepness increases and they break to form whitecaps. In a steady wind, waves of various dimensions develop with progressively increasing heights and periods until a steady state is reached in which the surface is fully developed for the prevailing wind speed (table 2-1). This steady state, known as seas, is maintained as long as the wind remains constant. Wind Ripple Chop Wind Waves Sea Swell Wave Development Energy Traveling in Waves FIGURE 2-3. WAVE DEVELOPMENT AND MOVEMENT As Used at sea As Used on land Beaufort Wind Nautical feet per indications Wind standard mph indications Interna- miles per second at sea Recorded at on Land tional hours 33 ft. above Number (Knots) ground level 0 Calm <1 <2 Sea mirror smooth Calm <1 Smoke rises vertically 1 Light Air 1-3 2-5 Sm.scale wavelets, Light Air 1-3 Direction shown by no foam crests smoke but not by wind vanes 2 Lt. Breeze 4-6 6-11 Waves short and more Lt. Breeze 4-7 Wind felt on face; pronounced; crests ordinary vanes move 3 Gentle Breeze 7-10 12-18 begin to break; foam leaves rustle has glassy look Gentle Breeze 8-12 Leaves and small twigs in motion; wind extends flag 4 Mod. Breeze 11-16 19-27 Waves are longer Mod. Breeze 13-18 Raises dust and waste paper, small branches moved 5 Fresh Breeze 17-21 28-36 Waves Pronounced & Fresh Breeze 19-24 Sm.Trees in leaf begin long white foam crest to sway 6 Strong Breeze 22-17 37-46 Larger Waves; white Strong Breeze 25-31 Lg.Branches in motion foam crests more whistling heard in extensive telephone wires 7 Strong Wind 28-33 47-56 Sea heaps up,wind Mod. Gale 32-38 Whole trees in motion blows foam in streaks difficult to walk against wind 8 Fresh Gale 34-40 57-68 Height of waves& crests Fresh Gale 39-46 Breaks twigs off trees, increases visibly; foam greatly impedes progress 9 Strong Gale 41-47 69-80 blown in denser streaks Strong Gale 47-54 Slight structural damage 10 Whole Gale 48-55 81-93 High waves with long Whole Gale 55-63 Seldom experienced overhanging crests; inland; trees uprooted, great foam crests considerable structural damage 11 Storm 56-65 94-110 Waves that hide ships Storm 64-75 Very rarely experienced; within the troughs; sea widespread damage covered with streaky results 12 Hurricane >65 >110 foam; spray fills air. Hurricane >75 TABLE 2-1. THE BEAUFORT WIND SCALE
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