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AI.II.L.K1hFAA-S-ACS-25 · Nov 2023Knowledge

h. Direction and height of waves

ACS element text (the applicant demonstrates understanding of)

Characteristics of a water surface as affected by features, such as: h. Direction and height of waves

Bottom line

Wave height is measured from the bottom of the trough to the top of the crest. Wave height depends on windspeed, the length of time the wind blows over the water, and the distance over which the wind acts on the water. Waves are perpendicular to the wind direction, while wind streaks on the water are parallel to the wind.

Key numbers

Key numbers for h. Direction and height of waves
NumberWhat it means
about 2 knotsRipples form
4 knotsSmall waves
above ~8 knotsWind streaks
12 knotsBreaking crests
lower than 12 to 15 feetMost ocean swells

FAA references

  1. SEA ch. 3 (p. 3-1) — FAA-H-8083-23
  2. SEA ch. 3 (p. 3-2) — FAA-H-8083-23
  3. AIM 6-3-3 (Ditching Procedures) — AIM Basic 2/20/25 w/ Change 1 (8/7/25) & Change 2 (1/22/26)
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