SB - Water current detection and mapping

The SB-module lets the Olex detect and map water currents. By analyzing five NMEA data types - position, speed over ground, course over ground, true heading, and speed through water - the vessel drift related to ground is calculated and shown as a variable-size arrow pointing away from the ship. This drift is assumed to be representative of the water current.

In addition to vizualizing realtime water current, the SB module also allows the Olex to collect currents values and save them in a cell-like structure, much like the seabed database. The mapping takes the main tidal phase into account. Each calulated current detection is mapped in time slices synced to the moon's angle from the earth at the time of the detection (the so-called M2 tidal constituent).

Instuments

One can use surprisingly simple instruments for this current mapping. This is possible because Olex does a good job in calibrating the sensors, recognizing various short-term errors, and using GPS positions for prediction validation.

Calibration

Regardless of what water speed sensor is used, it has to be calibrated for nonlinear speed response due to water flow patterns. The Olex has a special mode where it asks the skipper to steer opposing straight lines at various speeds, automatically working out a graph of apparent water speed and correction factors. Same for the heading sensor. This procedure will likely only be done during initial water trials, but can be repeated by the skipper if deemed necessary.