Wind Data at Sea . The wind direction is observed in relation to the ship's bow so that the wind direction in relation to true north is affected by the ship's direction. The wind speed and direction, with the affect of the ship's speed and direction, is the apparent or relative wind. The wind speed and direction, minus the affect of the ship's speed and direction, is the true wind. 2.8.1.2 Units of Measure .
Wind direction is observed to the nearest whole degree and computed to the nearest ten degrees.
2.8.1.3 Accuracy . Since true wind must be computed, the chance of committing an error is increased. True wind or estimates are one of the most important observations made by ships at sea since the data reported in the ship synoptic code is used as criteria for issuance of wind, storm, high seas warnings, and ship routing forecasts. Therefore, care must be taken whenever computing true wind data. Observing Wind Data .