[CA] [CA11] Speed over ground vs through water

[Chuck - Raymarine - Moderator]

Welcome to the Raymarine Forum Philip,

STW sensors must be calibrated via the instrument which they have been interfaced to (see the Calibration section of the ST60/ST60+ Speed/Tridata instrument's owner's guide). Calibration should be performed under slack conditions and will accordingly only equal SOG under such conditions. STW sensors have non-linear error. Accordingly, the reported speed value will be closest to SOG when the vessel is operating under slack conditions and at the speed of operation during calibration. Some more advanced STW instruments (ex. i70S/i70 MFIDs w/iTC-5 Analog Instrument Transducer Converter) support multi-point STW calibration.