Page 62 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

50 CHAPTER 2 The Ocean Environment
Table 2.5 Beaufort Scale (Thurman 1994)
Beaufort Surface Winds in Seaman’s
No. m/s (mph) Description Effect at Sea
0 ,1 (,2)
1 0.3
1.5 (1
3)
2 1.6
3.3 (4
7)
3 3.4
5.4 (8
12)
4 5.5
7.9 (13
18)
5 8.0
10.7 (19
24)
6 10.8
13.8 (25
31)
7 13.9
17.1 (32
38)
8 17.2
20.7 (39
46)
9 20.8
24.4 (47
54)
10 24.5
28.4 (55
63)
11 28.5
32.6 (64
72)
12 32.7
36.9 (73
82)
Calm Light air
Light breeze Gentle breeze Moderate breeze Fresh breeze Strong breeze Near gale
Gale
Strong gale Storm
Violent storm
Hurricane
Mirror-like sea
Ripples with appearances of scales; no foam crests
Small wavelets; crests of glassy appearance,
no breaking
Large wavelets; crests beginning to break; scattered whitecaps
Small waves, becoming longer;
numerous whitecaps
Moderate waves, taking longer to form;
many whitecaps; some spray
Large waves begin to form; whitecaps everywhere; more spray
Sea heaps up and white foam from breaking waves begins to be blown in streaks
Moderately high waves of greater length; edges of crests begin to break into spindrift; foam is blown in well-marked streaks
High waves; dense streaks of foam and sea begins to roll; spray may affect visibility
Very high waves with overhanging crests; foam is blown in dense white streaks, causing the sea to appear white; the rolling of the sea becomes heavy; visibility reduced
Exceptionally high waves (small- and medium- sized ships might be for a time lost to view behind the waves); the sea is covered with white patches of foam; everywhere the edges of the wave crests are blown into froth; visibility further reduced
The air is filled with foam and spray; sea completely white with driving spray; visibility greatly reduced
Described here are the basic components of ocean waves in an idealistic form to allow the anal- ysis of each component individually. As described in Thurman (1994):
As an idealized progressive wave passes a permanent marker, such as a pier piling, a succession of high parts of the wave, crests, will be encountered, separated by low parts, troughs. If the water level on the piling were marked when the trough passes, and the same for the crests, the vertical distance between the marks would be the wave height (H). The horizontal distance between corresponding points on successive waveforms, such as from crest to crest, is the wave- length (L). The ratio of H/L is wave steepness. The time that elapses during the passing of one