📘 This glossary brings together the main terms used in the Navimetrix application and its FAQs. It helps users better understand concepts related to navigation, routing, and marine weather.

Course Over Ground (COG)

The actual direction of the boat’s movement over the seabed, expressed in degrees relative to true north. It differs from the compass heading when there is drift caused by wind or current.

Speed Over Ground (SOG)

The boat’s actual speed relative to the ground (not the water). Calculated by GPS, it includes the effect of currents.

Heading (HDG)

The direction in which the boat’s bow is pointing, measured relative to true or magnetic north.

True Wind Angle (TWA)

The angle between the boat’s axis and the true wind direction. It is calculated from the apparent wind and the boat’s speed.

True Wind Speed (TWS)

The wind speed derived from the apparent wind and the boat’s speed. It represents the actual wind strength on the sea surface.

Apparent Wind Angle (AWA)

The wind angle felt on board, influenced by the boat’s motion. Measured relative to the boat’s centerline.

Apparent Wind Speed (AWS)

The wind speed felt on the boat, resulting from the combination of the true wind and the boat’s speed.

Velocity Made Good (VMG)

The useful component of the boat’s speed, indicating the effective progress toward the destination or upwind.

Closest Point of Approach (CPA)

The point at which two vessels will be at their minimum distance from each other, based on their current courses and speeds.

Time to CPA (TCPA)

The time remaining before reaching the CPA, used for collision avoidance and AIS alarms.

Bearing

The angle between north and the direction of an observed object from the boat. Used to determine the relative position of a target or coastline.

Depth

The water depth below the keel, measured by an echo sounder. A key parameter for safe navigation.

Waypoint (POI / Waypoint)

A geographic point used to define a route or a key position. In Navimetrix, POIs represent these waypoints.

GRIB File (Gridded Binary)

A standard file format containing numerical weather forecasts (wind, waves, pressure, temperature, etc.).

Isochrone

A curve connecting all possible boat positions at a given time according to the predicted weather conditions.

Routing

The calculation of an optimal route considering wind, waves, currents, and the boat’s performance.

Polar

A performance curve showing the boat’s speed as a function of wind angle and wind strength. It forms the basis for the routing engine.

Estimated Time of Arrival (ETA)

The predicted time of arrival at the destination, calculated from the remaining distance and the average speed.

Sea State

A description of the waves and swell (height, direction, period). Used to assess routing comfort and safety.

Swell

A regular train of waves formed by distant winds. It differs from the wind sea, which is generated locally.

Significant Wave Height

The average height of the highest one-third of waves, the main indicator of overall sea conditions.

Currents

Water movements caused by tides or ocean circulation. They affect the boat’s speed and trajectory.

Tide

Variation in sea level caused by the gravitational attraction of the Moon and the Sun. It influences depth and coastal currents.