#### Configuration and Operational Features

| Menu path |
|-------------|
| {{ menu }} → {{ settings }} → Sensors → Add sensor → Speed Log |

The sensor connection and setup are performed in accordance with the {doc}`procedure </sections/sensors/navigation-sensors/index>`.

Speed through water or speed over ground sensor: **Speed Log** or **{doc}`INS </sections/sensors/ins/index>`**.

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

![STW Sentences](images/STW_2.png)

- **VBW** — dual ground/water speed (Dual Ground/Water Speed);
- **VHW** — water speed and heading (Water Speed and Heading).<br><br>
  
#### Speed Sensor Operational Features

Vessel speed is displayed on the following interface elements:
- **{doc}`Navigational Panel </sections/graphical-user-interface/navigational-panel/index>`**
- **Log book** in the **{doc}`Standard Position </sections/navigational-log/standard-position/index>` (Track) section**

![Navigation Panel](images/STW_1.png)

| 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.

![Speed discrepancy](images/STW_3.png)

| 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: <sensor name> | 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. |
