## Echo Sounder Operational Features

The echo sounder measured depth is displayed in:
- **{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**

```{important}
When changing the primary echo sounder (for example, if the current sensor fails), verify the correction settings in the **Echo Settings** window. Corrections may differ between sensors depending on the transducer installation location.
```

### Navigational Panel

The current measured depth value is displayed on the navigational panel.

```{danger}
Note that the echo sounder measures the actual depth, which may differ from the ENC depth.

Priority should be given to the measured depth.
```

![Navigational panel](images/ECHO_2.png)

| No. | Element | Description |
|---|---------|----------|
| **1** | Measured depth | The value of depth measured and corrected by echo sounder corrections. Received from sentences: `$--DBT`, `$--DPT` |
|  | **DPT** | Navigation parameter name — depth |
|  | **Echo_Bow** | Navigation parameter source name |
| **2** | Drop-down list | Sets the depth reference line displayed on the echogram. Options: **Waterline** — depth from waterline; **Transducer** — depth from echo sounder transducer; **Keel** — depth under keel.<br>![Depth reference line](images/ECHO_5.png)<br>Depth recalculation is performed based on the values entered in the echo sounder settings in ECDIS |

### Echogram (Echo)

When an echo sounder is added to ECDIS, the **ECHO** tab will appear in the multifunction window.

![Echogram](images/ECHO_3.png)

| No. | Element | Description |
|---|---------|----------|
| **1** | **Scale** drop-down list | Changes the echogram scale.<br>![Echogram scale](images/ECHO_4.png) |
| **2** | Drop-down list | Sets the depth reference line displayed on the echogram. Options: **Waterline** — depth from waterline; **Transducer** — depth from echo sounder transducer; **Keel** — depth under keel.<br>![Depth reference line](images/ECHO_5.png)<br>Depth recalculation is performed based on the values entered in the echo sounder settings in ECDIS |
| **3** | **Settings** | Go to [settings](#echo-sounder-transducer-settings) for **depth monitoring** |
| **4** | Echogram scale | In meters ({doc}`units of measurement </sections/system-settings/measurement-units/index>`) |
| **5** | Echogram | Graphical depth display |
| **6** | Current **depth** value | Current depth with corrections applied |
| **7** | Time stamp | The point in time at which the depth was measured |
| **8** | **Dangerous isobath** | Entered in {doc}`vessel dimensions </sections/vessel-settings/vessel-dimensions/index>` |
| **9** | Time marks | On the echogram |
| **10** | Water temperature | Received from the echo sounder, in degrees Celsius. Received from sentence: `$--MTW` |

```{note}
The echogram displays data in real time and allows visual assessment of the seabed topography beneath the vessel and the trend of its change. It is recommended to regularly review the echogram to monitor abrupt depth changes, especially when navigating in waters with numerous navigational hazards and in shallow waters.
```

```{important}
When interpreting echo sounder data, remember that the readings reflect the depth from the established reference point.

The reference line is set by the navigator independently, depending on prevailing circumstances: use **Keel** for monitoring under-keel clearance, use **Waterline** for comparison with the chart.
```

```{warning}
The echo sounder measures depth at the current moment in time. When the vessel is moving at high speed or in heavy sea conditions, echo sounder data may have delays or inaccuracies. Consider the dynamics of vessel movement and compare echo sounder readings with ENC data.
```

The echogram displays **15 minutes of echo sounder operation**. To view previous depth values on the echogram — press and hold the left mouse button (touch and hold) on the chart and move the cursor (finger) to the right.

To return to current readings: left-click (tap) the current time stamp indicator.

```{tip}
For more effective use of the echogram, it is recommended to set the echogram scale considering the expected depths on the upcoming route segment. This improves chart readability and provides better assessment of the seabed topography.
```

### Echo Sounder Transducer Settings

Go to **Echo Settings:**

| Menu path |
|-------------|
| {{ menu }} → {{ settings }} → Echo Settings |
| Echo → Echo Settings |

**Echo sounder** correction settings. Selection of the echo sounder transducer sentence for correct depth calculation.

The echo sounder can simultaneously transmit sentences `$--DBT` and `$--DPT`. After configuring the depth sensor, the NMEA sentence and the transducer position on the vessel hull must be configured.

#### Settings with `$--DBT` Sentence

![Echo sounder settings](images/ECHO_6.png)

#### Settings with `$--DPT` Sentence

![Echo sounder settings](images/ECHO_8.png)

When entering correction parameters, the following equality must be satisfied:

$$\Delta Z_{T} + \Delta Z_{K} = \text{Draught}_{WL}$$

where:

- $\Delta Z_{T}$ — transducer offset from waterline
- $\Delta Z_{K}$ — transducer offset from keel (element 6)
- $\text{Draught}_{WL}$ — vessel draught at the design waterline

If the equality is not satisfied, a message appears at the bottom of the window.

| No. | Element | Description |
|---|---------|----------|
| **1** | **Active echo sounder** | Primary echo sounder name |
| **2** | **Echo sounder data** | Data values from sentences transmitted by the active echo sounder |
| **3** | **For calculation use this sentence** (drop-down list) | Selection of the sentence (`$--DBT` or `$--DPT`) whose data will be used for depth calculations |
| **4** | **Calculated depth** | Depth value calculated with the entered corrections |
| **5** | **Transducer offset from WL** | Set in the range from 0 to 29.9 m, default 0. Constant value for a fixed echo sounder. The equality $\Delta Z_{T} + \Delta Z_{K} = \text{Draught}_{WL}$ must be satisfied |
| **6** | **Transducer offset from keel** | Set in the range from 0 to 29.9 m, default 0. Constant value for a fixed echo sounder. The equality $\Delta Z_{T} + \Delta Z_{K} = \text{Draught}_{WL}$ must be satisfied |
| **7** | **Depth from transducer (DPT)** | Measured depth value from transducer to bottom |
| **8** | **DPT Offset +** | Distance from transducer to keel |
| **9** | **Echo scale** | Echo sounder operating scale. Transmitted only in the `$--DPT` sentence |
| **10** | **Water temperature** | Water temperature. Transmitted only in the `$--MTW` sentence |
| **11** | **Depth from surface** | Calculated depth from the water surface |
| **12** | **Depth from transducer** | Depth from the echo sounder transducer |
| **13** | **Clearance (Depth from keel)** | Calculated depth under keel |

```{warning}
Echo sounder correction values affect all depth and under-keel clearance calculations in ECDIS. An error in correction settings may result in underestimation or overestimation of depth, creating a direct threat to navigation safety.
Always verify that the equality $\Delta Z_{T} + \Delta Z_{K} = \text{Draught}_{WL}$ is satisfied and compare readings with cartographic data.
```

#### Echo Sounder Warnings

| **TEXT** | **CATEGORY** | **CONDITION** |
|-----------|---------------|-------------|
| Echo sounder sensor malfunction \<sensor name\> | Alarm | When data from the sensor stops being received according to the configurable timeout. |
| Check depth \<sensor name\> | Warning | The measured under-keel clearance from the echo sounder is less than or equal to the check depth value set in the settings (element 4 of the "Alerts" table). |
| Dangerous under-keel clearance \<sensor name\> | Warning | The measured under-keel clearance is less than or equal to the sum of the minimum under-keel clearance from vessel dimensions (section 6.2) and the value from the "Approaching under-keel clearance" field (element 2 of the "Alerts" table). |
| Minimum under-keel clearance \<sensor name\> | Alarm | The measured under-keel clearance is less than or equal to the under-keel clearance value set in vessel dimensions. |
| Depth less than dangerous isobath: \<sensor name\> | Alarm | The measured total depth is less than or equal to the dangerous isobath value set in the settings. |

### Echo Sounder Usage Recommendations

```{important}
The echo sounder is an auxiliary navigation tool and should be used in combination with other sources of depth information: ENC, visual observation. Do not rely solely on echo sounder readings when making decisions.
```

```{warning}
Echo sounder readings may be distorted under the following conditions:
- High vessel speed (measurement inertia)
- Heavy sea conditions
- Presence of seaweed, soft bottom, gas bubbles in the water column
- Low water temperature (possible changes in sound speed)
- Improper transducer operation due to fouling or mechanical damage
```
