WIND 27 



EXAMPLE: 



3331.1. APPARENT WIND IS OFF STARBOARD BOW 



(a) Ship's heading 270° true 



(b) Apparent wind (relative to ship's bow) ...... 040 ° 



(c) True bearing . . . 310° 



3331.2. APPARENT WIND IS OFF THE PORT BOW 



(a) Ship's heading 270° true 



(b) Apparent wind (relative to ship's bow) - 040 ° 



(c) True bearing. . . 230° 



3332. The procedure for computing true wind direction and speed with 

 the aid of a plotting board follows: From the center of the board or from the 

 pin, a scale is ruled off equal-distant on top and bottom of the scale, from 

 to 50. Should the apparent windexceed 50 knots, the scale may be doubled 

 and the computing procedure carried on as described. At the top of the 

 board is a red arrow. In this discussion when referring to the top of the 

 board, it will be with reference to this arrow. An example of how the 

 method is used is outlined below: 



(a) Ship's course and speed 270° - 15 knots 



(b) Apparent wind (wind relative to ship's bow) 040° - 20 knots 



(c) Apparent wind converted to a true bearing 310° 



3332.1. Set 270 degrees at the index on top of the plotting board; using 

 any convenient linear scale, measure vertically downward from the center 

 peg of the plotting board a distance equivalent to 15 knots. Mark this spot 

 "S" (for ship). Rotate the protractor disk of the plotting board until 310 de- 

 grees is at the index (red arrow) at the top of the plotting board. Using the 

 same linear scale as for ship's speed, plot vertically downward from the 

 center peg of the plotting board a distance equivalent to 20 knots. Mark this 

 point "W." Rotate the protractor disk until the "S" is vertically above the 

 "W," using the vertical lines on the plotting board to line up the two points. 

 Read the true wind direction at the TOP of the plotting board. The distance 

 between points "S" and "W" is the true wind speed, using the same scale as 

 in plotting the points "S" and "W." The true wind direction is 357 degrees 

 and the speed is 13 knots. 



3332.2. Anemometer equipped vessels may obtain a plotting board by re- 

 quest in accordance with J 1301. 



