Sea Navigation Practice Test 2025 - Free Sea Navigation Practice Questions and Study Guide

To achieve a 3D fix in satellite navigation, a minimum of four satellites is necessary. This is because a 3D fix provides both positional information—latitude and longitude—and elevation. Each satellite contributes to calculating the ship's position and orbit through triangulation, which requires data from multiple satellites.

Three satellites can provide a 2D fix, determining latitude and longitude but not elevation. The fourth satellite is critical for calculating the altitude and correcting for any discrepancies caused by satellite clock errors. Without this fourth signal, the system cannot accurately pinpoint the observer's position in three-dimensional space. Thus, having four satellites allows for a comprehensive and accurate location fix in terms of latitude, longitude, and height above the reference point, such as sea level.