26 



MANUAL OF MARINE METEOROLOGICAL OBSERVATIONS 



3330. PLOTTING BDARD METHOD FOR COMPUTING TRUE WIND 

 AT SEA, Ships that are not equipped with wind transmitting and indicating 

 instruments should estimate the apparent wind direction and wind speed in 

 accordance with instructions contained in 3F3310.1. True wind maybe 

 computed with the aid of a plotting board. Anemometer equipped vessels 

 should obtain apparent wind direction and speed from wind indicators. 

 The true wind may be determined from the apparent wind relative to the 

 ship's bow, and from the course and speed of the ship. 



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Figure 3. -- Shipboard Wind Plotter 



3331. The apparent wind is a resultant of the true wind direction and 

 speed or movement of the ship. The apparent wind relative to the bow of 

 the ship is converted to a true compass bearing by adding the apparent wind 

 direction to the ship's heading if the wind is off the starboard bow and 

 subtracting the 5.pparent wind direction if the wind is off the port bow; 



