When GNSS signals are suspected of being manipulated, the priority is to preserve a trustworthy navigation solution while the situation is assessed. Rebooting or power-cycling GPS receivers can cause them to re-acquire signals that may still be spoofed, reintroducing a misleading position and time fix. That’s why the recommended action is not to restart the GPS systems. Instead, rely on other navigation sources to maintain safety: use radar to verify relative positions to known objects, gyro or flux gate for heading, the ship’s speed log for motion, and perform dead reckoning to sustain a current track. Cross-check any GPS-derived data with these independent sources, and only resume full GNSS trust after confirming the spoofing issue has been resolved through proper procedures. If applicable, report the anomaly per ship’s protocols and engage the appropriate authorities.

High-pressure systems feature sinking air that spreads out at the surface, creating outward flow from the center. In the Northern Hemisphere, the Coriolis effect deflects this outward motion to the right, resulting in a clockwise circulation around the center. Because the pressure gradient is usually gentle for a broad high, the winds are typically light and slow-moving. This combination—outward and clockwise winds around the center, slow movement, and generally fair, stable weather—best describes a high-pressure system. By contrast, a low-pressure system draws air inward toward the center and tends to bring clouds and storms, and winds crossing isobars isn’t the defining pattern of a steady high.

Horizontal datum is the reference model that tells you where coordinates on a chart actually sit on the Earth. For nautical charts, the standard global reference used is WGS-84 because it aligns with GPS data and is adopted across modern charts to keep fixes and chart positions consistent worldwide. Using WGS-84 ensures that a position derived from GNSS matches the charted position without offsets. Other options like NAD83, ETRS89, or ED50 are regional or older datums and can introduce mismatches if used instead of the global standard.

Azimuth is the horizontal angle measured clockwise from true north. This north reference line provides a fixed baseline so directions can be expressed consistently; 0° points to north, 90° to the east, 180° to the south, and 270° to the west. In practice, you take the direction to the object and measure the angle clockwise from that north line. If you used a different reference line, the numbers would shift accordingly.