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BY: Gian Gabriel P. Ibo
Deck Cadet
*
*If an instrument for
measuring the speed and
direction of the wind is
mounted on shore, then the
readings obtained are those
of the speed and direction
of the true wind.
*If we take this same
instrument, and mount it on
a boat that is moving
through the water, then the
reading will be quite
different from those taken
on shore. These readings
show the speed and
direction of the apparent
wind relative to the boat.
*
For Example
If true wind is blowing easterly
@10kts then a vessel is traveling
easterly @20kts
TO UNDERSTAND TRUE
AND APPARENT WIND
We can say that apparent wind speed
Will be @30kts
10kts
20kts
TRUE WIND AND DIRECTION
CALCULATION
A ship is heading at 025 with a speed of
12.5 kts
Ship’s wind indicator reading is at -030 with a speed of
20kts
TIP: If wind is
in Port side (-)
If wind is in
Stbd side (+)
Ships Wind
Direction
Indicator
To Get apparent
Wind direction
360
025(+) Heading
030(-)
355- Apparent wind
USING A TRIANGLE AND A COMPASS DIVIDER MARK THE
HEADING OF THE SHIP AND ITS CORRESPONDING SPEED
BY THE USE OF THE COMPASS DIVIDER ON THE SPEED
SCALING
10
5
Ships heading 025
@12.5kts
AFTER THAT MARK ALSO THE APPARENT WIND
DIRECTION AND ITS SPEED
Ships heading 025
@12.5kts
20
15
10
5
Ships heading 025
@12.5kts
20
15
10
5
Ships heading 025
@12.5kts
20
15
10
5
Apparent Wind
355
@20kts
NEXT IS YOU NEED TO MAKE A LINE FROM THE
TIP OF THE SHIPS HEADING AND THE APPARENT WIND
THEN DRAG IT INTO THE CENTER POINT USING A TRIANGLE
IN ORDER TO GET THE TRUE WIND DIRECTION
Ships heading 025
@12.5kts
20
15
10
5
Apparent Wind
355
@20kts
Ships heading 025
@12.5kts
20
15
10
5
Apparent Wind
355
@20kts
NOW MEASURE THE VECTOR OF THE TRUE WIND
BY USING THE COMPASS DIVIDER
IN ORDER TO GET THE TRUE WIND SPEED
Ships heading 025
@12.5kts
20
15
10
5
Apparent Wind
355
@20kts
Ships heading 025
@12.5kts
20
15
10
5
Apparent Wind
355
@20kts
True wind
Direction: NW
Speed @ 12KTS
SO WE CONCLUDE THAT THE TRUE WIND DIRECTION IS
AT NORTH WEST AND THE TRUE WIND SPEED IS AT 12KTS
IN ORDER NOT TO BE CONFUSE IN GETTING THE DIRECTION
OF THE TRUE WIND JUST FOLLOW THIS SIMPLE GUIDE
H-HEADING
A-APPARENT
T-TRUE
T-TRUE
A-APPARENT
H-HEADING
Ships heading 025
@12.5kts
20
15
10
5
Apparent Wind
355
@20kts
True wind
Direction: NW
Speed @ 12KTS
T
A
H
THANK YOU AND GODBLESS

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True wind speed and direction calculation and plotting