To verify position and measure distance off shore, mariners commonly rely on which navigation technology?

• A. GPS
• B. Radar
• C. Sonar
• D. AIS

Answer: (A)

Verifying your exact position and how far offshore you are relies on a system that provides precise, real-time coordinates. GPS does this by using signals from satellites to compute latitude and longitude, so you always know exactly where you are and can calculate distance from the shore by comparing those coordinates to a known coastline. Radar can show land in range and give you the distance to shore on the radar display, but it provides relative information unless you’ve already tied it to a fixed position, and it isn’t an exact geographic fix. Sonar measures depth beneath the keel, not your horizontal position or how far you are from shore. AIS transmits other ships’ positions and your own, but it depends on data from vessels and isn’t a primary independent position fix. So GPS is the most reliable way to verify position and measure distance off shore.