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Wind, Continued
Calculating
Once the relative wind direction and speed have been observed and the
True Wind
ship’s course and speed recorded, the true wind can be computed. The
Using the True
True Wind Computer (CP 264/U) is the quickest and easiest method.
Wind
Detailed instructions on the use of the True Wind Computer can be
Computer
found in Chapter 10 of the Manual for Ship’s Surface Weather
Observations, NAVOCEANCOMINST 3144.1C.
Calculating
True Wind
Using the
Maneuvering
Board
The use of the maneuvering board (MB) is by far the most accurate
method of determining true wind. The MB uses exact vectors to
establish apparent wind and own ship’s speed. The use of vectors
makes this method more precise.
Information on calculating true wind can be found in Pub 217
Maneuvering Board Manual, therefore it will not be duplicated here.
Pub 217 also contains solutions for finding desired wind, closest point of
aproach, and several other vector solutions that are invaluable to the
Quartermaster assisting the officer of the deck.
Computation
Check
No matter which method of computation is used to derive the true wind
direction and speed, the observer should check the results by applying
the following rules:
Rule 1: The true wind direction is always on the same side of the ship
as the apparent wind direction, but farther from the bow than the
apparent wind direction.
Rule 2: When the apparent wind direction is abaft the beam, the true
wind speed is greater than the apparent wind speed.
Rule 3: When the apparent wind direction is forward of the beam, the
true wind speed is less than the apparent wind speed.
10-25
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