## Dead Reckoning

**Dead Reckoning** — *the process of continuously and sequentially accounting for the elements of vessel movement — course and distance travelled — relative to an initial point, for the purpose of determining and predicting the vessel position at any given time*.

**Dead Reckoning** *is based on the continuous accounting of the direction and magnitude of vessel displacement over time.*

| Menu path |
|-------------|
| {{btn_DR}} |

### Transition to dead reckoning mode

ECDIS transitions to **dead reckoning mode** in the following cases:

- Automatically when GNSS receiver data is unavailable
- When an {doc}`observation </sections/instruments/manual-observations/index>` performed by manual methods is accepted for dead reckoning

### DR mode operating features

ECDIS automatically switches to **dead reckoning mode** without applying set and drift — **DR**. Dead reckoning starts from the last valid position; COG/SOG calculation is discontinued.

If speed (STW) and/or heading (HDG) sensors are available, coordinates are calculated from compass and log data.

```{important}
When navigating by dead reckoning, errors accumulate. To correct the growing error, it is recommended to correct the coordinates using manual and other backup position-fixing methods.
```

![DR/Manual Input window](images/DR.png)

| № | Element | Description |
|---|---------|----------|
| **1** | **Dead reckoning** | Dead reckoning elements |
| **2** | **Drift** | Drift elements |
| **3** | **Correction** | Entry of permanent corrections to navigational parameters |

![DR/Manual Input window](images/DR_2.png)

| № | Element | Description |
|---|---------|----------|
| **1** | **Dead reckoning coordinates** | Dead reckoning coordinates. When dead reckoning mode is off, data from the primary position sensor is fed to these fields. To shift the vessel position to entered coordinates (for example, after determining coordinates by astronomical methods) — press **Apply** |
| **2** | **Apply** | Applies the entered coordinates. Available when DR mode is on |
| **3** | **Forced DR mode activation** | Toggle for forced activation of dead reckoning mode |
| **4** | **Go to Manual Observations** | Go to {doc}`Manual Observations </sections/instruments/manual-observations/index>` for vessel position correction |
| **5** | **Manual course input** | Manual course input. When selector (6) is off, data from the heading sensor is fed to this field |
| **6** | **Enable manual course input** | Selector to enable manual course input |
| **7** | **Manual speed input** | Manual speed input. When selector (8) is off, data from the speed sensor is fed to this field |
| **8** | **Enable manual speed input** | Selector to enable manual speed through water input |

![DR/Manual Input window](images/Correction.png)

| № | Element | Description |
|---|---------|----------|
| **9** | **Latitude correction** | Enter latitude correction |
| **10** | **Longitude correction** | Enter longitude correction ![Position correction](images/Corr_POS.png)|
| **11** | **Course correction** | Enter course correction ![HDG correction](images/Corr_HDG.png)|
| **12** | **Speed correction** | Enter speed correction ![STW correction](images/Corr_STW.png)|

![DR/Manual Input window](images/Drift.png)

| № | Element | Description |
|---|---------|----------|
| **13** | **Set and drift speed** | Set the set and drift speed |
| **14** | **Set and drift direction** | Set the set and drift direction. In ECDIS, the set and drift direction is **directed from the compass** |
| **15** | **Set and drift timer** | Set and drift timer. Maximum set and drift accounting time is 3 hours. The timer starts when selector (16) is enabled and when set and drift parameters are changed. **5 minutes** before the set and drift accounting time expires, ECDIS displays a notification with a countdown: ![Set and drift timer warning](images/drift-timer-warning.png) When the set and drift accounting time expires, ECDIS discontinues set and drift accounting and generates a notification: ![Set and drift timer expired](images/drift-timer-expired.png) |
| **16** | **Set and drift enable selector** | Toggle to enable set and drift accounting |

### Simple dead reckoning mode

When ECDIS transitions to **Dead Reckoning (DR)** mode, the navigational indicator displays the data source — **DR**, and the values are highlighted in yellow.

![Chart in dead reckoning mode without set and drift](images/dr-mode-map.png)

| № | Element | Description |
|---|---------|----------|
| **1** | **Dead reckoning vessel position** | Dead reckoning vessel position without set and drift; in dead reckoning mode, the coordinates field is orange |
| **2** | **Vessel speed vector** | Vessel speed vector |
| **3** | **DR mode indicator** | **DR** — indicator of dead reckoning mode without set and drift |

### Set and drift accounting

When set and drift accounting is enabled, ECDIS calculates the course over ground vector and the track line relative to the ground.

![Chart in dead reckoning mode with set and drift](images/ep-mode-map.png)

| № | Element | Description |
|---|---------|----------|
| **1** | **Dead reckoning vessel position with set and drift** | Dead reckoning vessel position with set and drift; in dead reckoning mode, the coordinates field is orange |
| **2** | **Position by alternative source** | Position by an alternative coordinate source. For example, from a GNSS receiver |
| **3** | **EP mode indicator** | **EP** — indicator of dead reckoning mode with set and drift |
| **4** | **Manual input indicator** | **MAN** — indicator of manual course and speed input |
| **5** | **Set and drift indication** | Indication of set and drift direction and speed on the navigational panel |
