Speed Through Water (STW) Sensor

Configuration and operation of the speed through water sensor (STW — Speed Through Water).

Configuration and Operational Features

Menu path
→ → Sensors → Add sensor → Speed Log

The sensor connection and setup are performed in accordance with the procedure.

Speed through water or speed over ground sensor: Speed Log or INS.

In the sensor settings, processing of received messages and checksum verification must be enabled.

Depending on the device type, speed logs transmit the following IEC 61162 sentence headers:

• VD — Doppler log (Doppler, other/general);

• VM — Induction log (speed log, water, magnetic);

• VW — Mechanical or hydrodynamic log (speed log, water, mechanical);

• IN — INS;

Recommended Sentence Set for the Speed Sensor

• VBW — dual ground/water speed (Dual Ground/Water Speed);

• VHW — water speed and heading (Water Speed and Heading).
  
  

Speed Sensor Operational Features

Vessel speed is displayed on the following interface elements:

• Navigational Panel

• Log book in the Standard Position (Track) section

No.	Field	Description
1	Speed	Speed received from the speed sensor. Received from sentences: $--VBW, $--VHW
	STW	Name of the navigational parameter — speed through water
	STW_Sec	Name of the sensor providing the data

Speed Discrepancy

When two or more speed sensors are connected to ECDIS, the discrepancy between the Primary and Backup sensors will be calculated.

No.	Element	Description
1		Primary Speed sensor with priority 0
2		Backup Speed sensor with priority 1
3	Discrepancy	Speed discrepancy between the Primary and Backup sensors

When speed through water (STW) data is received, ECDIS displays the water speed vector.

Important

When multiple speed logs transmitting $--VBW and/or $--VHW sentences are connected, it is recommended to:

• create each log as a separate navigational sensor;

• enable processing of only one $--VBW or $--VHW sentence per sensor.

When processing the $--VBW sentence, ECDIS calculates the water speed vector from the longitudinal and transverse components.

When a speed sensor is available, the following tasks are solved:

• total drift calculation;

• wind calculation;

• vessel motion with drift calculation;

• monitoring corridor construction.

Speed Sensor Warnings

TEXT	CATEGORY	CONDITION
STW error:	Warning	When data from the sensor ceases to be received beyond the configurable timeout.
STW sensor data invalid	Warning	In the $--VBW sentence, the Status field of the water speed contains the value V, meaning the data is invalid.