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spray may reduce visibility
Very high waves, with overhanging crests, sea white with
densely blown foam, heavy rolling, lowered visibility
Exceptionally high waves, foam patches cover sea,
visibility more reduced
Air filled with foam, sea completely white with driving
spray, visibility greatly 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.
400 Feet
150 Feet
20 Feet
15 Feet
Height-to-Length Ratio 1: 20
Height-to-Length Ratio 1: 10
Figure 8-2. Height-to-length ratio.
Ch 08.qxd 8/25/04 11:27 AM Page 8-2
8-3
5. To determine the swell length or distance
between crests in feet, multiply the square of the
swell period by 5. For example, using a 6-second
swell period, 62 multiplied by 5 equals 180 feet.
[Figure 8-4]
LOW RECONNAISSANCE
Perform the low reconnaissance at 500 feet to confirm
the findings of the high reconnaissance and obtain a
more accurate estimate of wind direction and velocity.
If the direction of the swell does not agree with the
direction noted at 2,000 feet, then there are two swell
systems from different directions. The secondary swell
system is often moving in the same direction as the
wind and may be superimposed on the first swell system.
This condition may be indicated by the presence
of periodic groups of larger-than-average swells.
The wind direction and speed can be determined by
dropping smoke or observing foam patches, whitecaps,
and wind streaks. Whitecaps fall forward with
the wind but are overrun by the waves. Thus, the foam
patches appear to slide backward into the direction
from which the wind is blowing. To estimate wind
velocity from sea surface indications, see figure 8-1.
SELECT LANDING HEADING
When selecting a landing heading, chart all observed
variables and determine the headings that will prove
the safest while taking advantage of winds, if possible.
Descend to 100 feet and make a final evaluation by
flying the various headings and note on which heading
the sea appears most favorable. Use the heading that
looks smoothest and corresponds with one of the possible
headings selected by other criteria.
Consider the position of the sun. A glare on the water
during final approach might make that heading an
unsafe option.
Use caution in making a decision based on the appearance
of the sea. Often a flightpath directly downswell
appears to be the smoothest, but a landing on this
heading could be disastrous.
SWELL SYSTEM EVALUATION
The purpose of the swell system evaluation is to determine
the surface conditions and the best heading and
technique for landing. Perform a high reconnaissance,
a low reconnaissance, and then a final determination of
landing heading and touchdown area.
HIGH RECONNAISSANCE
During the high reconnaissance, determine the swell
period, swell velocity, and swell length. Perform the
high reconnaissance at an altitude of 1,500 to 2,000
feet. Fly straight and level while observing the swell
systems. Perform the observation through a complete
360º pattern, rolling out approximately every 45º.
Fly parallel to each swell system and note the heading,
the direction of movement of the swell, and the direction
of the wind.
To determine the time and distance between crests, and
their velocity, follow these directions:
1. Drop smoke or a float light and observe the wind
condition.
2. Time and count the passage of the smoke or float
light over successive crests. The number of
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