TWA (True Wind Angle) and TWS (True Wind Speed) are critical parameters for understanding wind conditions and optimising sailing performance. They form the foundation of polar diagrams – read more on this…

Here’s what they mean and how they differ:

True Wind Angle (TWA)

• Definition: TWA is the angle between the direction the boat is travelling and the direction the true wind is coming from. It is measured in degrees.
• Reference: Always relative to the boat’s heading (not the compass or a fixed direction).
• Range:
  • 0°: Sailing directly into the wind (impossible for most sailboats).
  • 90°: Sailing with the wind coming directly from the side (beam reach).
  • 180°: Sailing directly away from the wind (dead downwind).

Practical Use:

• Determines the boat’s point of sail (e.g., close-hauled, beam reach, broad reach, run).
• Used to choose the optimal sail configuration for given conditions.

True Wind Speed (TWS)

• Definition: TWS is the actual speed of the wind as it would be experienced if the boat were stationary in the water.
• Reference: Independent of the boat’s motion (as opposed to Apparent Wind Speed, AWS, which accounts for the boat’s speed).
• Units: Typically measured in knots.

Practical Use:

• Helps decide the sail trim and the type of sail to use.
• Critical for safety, as it informs decisions about reefing sails in high winds or deploying lighter sails in light winds.

TWA vs. TWS in Performance

• TWA (True Wind Angle): Focuses on the direction of the wind relative to the boat’s heading.
• TWS (True Wind Speed): Focuses on the intensity of the wind.

Example in Polar Diagrams:

• A polar diagram plots boat speed at different TWAs for various TWS values.
• For instance, at a TWS of 10 knots, the polar might show the boat achieves maximum speed at a TWA of 45° upwind and 135° downwind.

By combining TWA and TWS, sailors make informed decisions to optimise speed, efficiency, and safety.