In both cases, the curve shows the boat’s position over the next 12 hours with the forecast winds.
- Constant TWA (dark green). The wind angle does not change: if the wind shifts, the heading turns with it. It suits following a wind that changes.
- Constant heading (red). The direction does not change: if the wind shifts, the TWA changes. It gives a straight path, easier to check near coasts or when the forecast wind varies little.
If the forecast wind does not change, the two curves stay close. These are forecasts: look at where they go before sending an order.
Going further: Reading the constant TWA and constant heading curves.