User manual

Part B Section Appendix A.1
08 WIND STRENGTH
It is not likely that PBY will operate on or off the water in high wind conditions or rough
water and with all operations it must be remembered that the operating limit for wave
height is two (2) feet only. This will normally mean operating in winds no stronger than 10-
15 knots. For example:
l
l
09 WIND DIRECTION
Wind vanes on the water, wind "shadows" along the up wind shore, smoke, flag
orientation, sails, and the direction moored boats face are all indicators of wind direction.
Take Off, approach and landing out of wind will introduce a cross wind component and
reduce the head wind component as occurs on land. Reference should be made to the
crosswind component graph
10 VISIBILITY
Calm No wind glassy water
Light Air 1-3 Knots ripples on the water
Light Breeze 4-6 Knots Small wavelets, crests glassy, waves <6’
Gentle breeze 7-10 Knots Large wavelets, crests may break, waves <10’
Moderate breeze 11-15 Knots small waves, frequent white caps, waves <16'
Fresh breeze 16-20 Knots Larger longer waves, some spray, waves < 24'
The atmosphere over the water surface and the refraction of light by the water surface
commonly produces optical illusions. The commonest are the poor and often dangerously
inaccurate depth perception associated with glassy water conditions and the occurrence of
"mirage" images particularly in hot conditions.
Water
11 WAVES
Waves are the product of wind action over the water surface. Waves may be described
according to their wavelength, speed of propagation through the body of water, period, and
height. The wave moves in the direction of the wind that created it but the water itself does
not need to be moving the same way.
Wave size depends on the wind strength, and the distance over which the wind has acted
to produce the wave (called the wave fetch). Thus waves caused by the same wind get
bigger with duration of wind action and will be bigger in larger bodies of water. Waves
produced by a wind that is no longer with them gradually weaken but may travel great
distances producing swells. Frequently, waves of different form travelling in different
directions may be present in the same body of water at the same time.
Some people refer to the waves with the currently occurring wind as "primary” or "live"
waves and those that have moved from their area of origin or were caused by a previous
wind as "secondary" or "dead" waves.
Waves will break whenever they reach a height of about 1/7 of their wavelength so this
can occur as wind strengthens and wave height increases (part of the formation of
whitecaps), or as the water depth decreases and the wave comes into "ground effect".
Here the wave height is increasing as the water depth decreases and the water in contact
with the bottom is slowed allowing the surface water to continue. Eventually the surface
Stichting Catalina PH-PBY Rev No: 02
01 April, 2006 Page: 3