Ch 08.qxd 8/25/04 11:27 AM Page 8-2 Sea surface smooth and mirror-like Scaly ripples, no foam crests Small wavelets crests glassy, no breaking Large wavelets crests begin to break, scattered  whitecaps Small waves becoming longer, numerous whitecaps Moderate waves taking longer form, many whitecaps,  some spray Larger waves whitecaps common, more spray Sea heaps up white foam streaks off breakers Moderately high, wa ves of greater length, edges of crests  begin to break into spindr ift, foam blown in streaks High waves sea begins to roll, dense streaks of foam,  spray ma reduce visibility Very high waves with ov erhanging crests, sea white with  densely blown foam, hea vy rolling, lowered visibility Exceptionally high w av es , f oam patches cover sea,  visibility more reduced Air filled with foam, sea completely white with driving  spray, visibility g reatly reduced Calm, glassy 0 Calm, rippled 0 — 0.3 Smooth, wavelets 0.3-1 Slight 1-4 Moderate 4-8  Rough 8-13 Very rough 13-20 High 20-30 Very high 30-45 Phenomenal 45 and over 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 10 11 12 Less than1 1-3 4-6 7-10 11-16 17-21 22-27 28-33 34-40 41-47 48-55 56-63 64 and over Beaufort  Number Wind  Velocity  (Knots) Calm Light Air Light Breeze Gentle Breeze Moderate Breeze Fresh Breeze Strong Breeze Near Gale Gale Strong Gale Storm Violent Storm Hurricane Wind  Description Sea State Description Term and  Height of  Waves (Feet) Sea State Condition Number BEAUFORT WIND SCALE WITH CORRESPONDING SEA STATE CODES Figure 8-1. Beaufort wind scale. the waves is the  height-to-length ratio [Figure 8-2]. This ratio is an indication of the amount of motion a seaplane experiences on the water and the threat to cap- sizing. For example, a body of water with 20-foot waves and a swell length of 400 feet has a height-to- length ratio of 1:20, which may not put the seaplane at risk of capsizing, depending on the crosswinds. However, 15-foot waves with a length of 150 feet pro- duce a height-to-length ratio of 1:10, which greatly increases the risk of capsizing, especially if the wave is breaking abeam of the seaplane. As the swell length decreases, swell height becomes increasingly critical to capsizing. Thus, when a high swell height-to-length ratio exists, a crosswind takeoff or landing should not be attempted. Downwind takeoff and landing may be made downswell in light and moderate wind; however, a downwind landing should never be attempted when wind velocities are high regardless of swell direction. When two swell systems are in phase, the swells act together and result in higher swells. However, when two swell systems are in opposition, the swells tend to cancel each other or “fill in the troughs.” This provides a relatively flat area that appears as a lesser concentra- tion of whitecaps and shadows. This flat area is a good touchdown spot for landing. [Figure 8-3] Figure 8-2. Height-to-length ratio. 8-2 400 Feet 150 Feet 20 Feet 15 Feet Height-to-Length Ratio 1: 20 Height-to-Length Ratio 1: 10