Understanding Wind Data on Raymarine Displays – Apparent, True, and Ground Wind for Sailing

Learn the difference between Apparent Wind, True Wind, and Ground Wind, why they are important, and how Raymarine displays calculate them.

Raymarine displays can show several different types of wind data, which sometimes causes confusion. Here we explain what each type means and what additional data is required to calculate them. We use English terms (AWA, AWS, TWA, TWS, GWD, GWS) as they are standard in sailing and reduce the risk of misunderstanding.

Angle or Direction?

Angle (e.g., Apparent Wind Angle, AWA) is relative to the boat's bow (0–180° port or starboard). Direction (e.g., Ground Wind Direction, GWD) is relative to north.

Apparent Wind

AWA and AWS are standard data on wind instruments like the Raymarine i60. These are measured directly by the masthead sensor and are affected by the boat's movement. Example:

• Sailing into a 15 kn breeze at 10 kn speed → AWS = 25 kn, AWA = 0° (wind on the bow).
• Sailing with the wind at the same speed → AWS = 5 kn, AWA = 180° (wind from astern).

True Wind

TWA and TWS are wind over water, not over ground. Calculated from AWA, AWS, and speed through water (STW). GPS speed (SOG) is not sufficient. For TWD (True Wind Direction), compass heading and STW are required. Multifunction displays and i70/i70S show these values.

Ground Wind

GWS and GWD are wind over ground, as you would measure from the dock. Requires AWA/AWS, GPS COG/SOG, and compass heading.

Why is Ground Wind less useful for sailing?

Sailing takes place in water, not on land. Ground Wind can differ greatly from True Wind in currents or tides. Therefore, sailing instruments show True Wind as standard.

Example: The difference between Ground Wind and True Wind

Scenario: You are sailing east from Sydney Harbour in an easterly breeze (Ground Wind 090° True) and a strong southerly current. The first image shows the situation without current:

With a 2+ kn southerly current, the difference becomes clear. If you steer by Ground Wind, you risk ending up in the no-go zone. Sailing by True Wind provides the correct course:

Summary

• Apparent Wind: Wind experienced on board, affected by boat speed.
• True Wind: Wind over water, calculated with STW and compass data.
• Ground Wind: Wind over ground, less relevant for sailing.

For best sailing performance: use True Wind for course and Apparent Wind for sail trim.