3.8.7 Chart Symbology

Chart symbols used on ENCs differ from traditional paper chart symbols.These symbols may change or be added from time to time. Manufacturers require to adhere to IHO guidelines and changes must be notified by manufacturer. Officers must be familiar with these symbols and any updates. The attached ‘Admiralty Quick Guide to ENC Symbols’ is a good reference document.

3.8.8 Ecdis Display a) Day / Night Modes

N avigating officers must familiarise themselves with the different colour schemes used to distinguish between different depths of water and land. The night palette may cause confusion for those who are unfamiliar with the alternative colour scheme used to distinguish between different depths of water.

Left: Day display.

Left: Night display.

B) Display Modes

Electronic Navigation Charts (ENCs) are constructed from different layers of information. Much of this information can be selected by the user. It is crucial that sufficient information is displayed to allow safe navigation of the vessel. ENC layers include:

• Base – Coastline, Traffic routeing systems, scale, range, orientation and display mode, units of depth and height, own ship safety contours, indication of isolated dangers which lie within the safe waters. ECDIS display modes that are set-up in ‘base’ display mode may remove vital information.

• Standard – Base plus, Drying line, Fixed and floating aids to navigation, boundaries of fairways, visual and radar conspicuous targets, Prohibited and restricted areas, Chart scale boundaries, Indication of cautionary notes.

• All Other Information – Standard plus, Spot soundings, Submarine cables and pipelines, Ferry routes, Details of isolated dangers, Details of aids to navigation, Contents of cautionary notes, ENC edition dates, Geodetic datum, Magnetic variation.

• Custom/Other– Standard plus user defined selected others from ‘All Other Information’.

Owing to the sophistication of ECDIS, potential problems with the planned route may not be immediately apparent, and can be heavily influenced by displaying either too many or too few layers.

The International Hydrographic Office have alsoissued a circular warning that ECDIS may not display some isolated shoal depths when operating in ‘base’ or ‘standard display’ mode. As a result, route planning and monitoring alarms may not always be activated when approaching such dangers and may result in groundings.

Mariners must ensure their ECDIS display is set-up appropriately to the prevailing circumstances and conditions so that it includes all information necessary for safe navigation. As a minimum, when using ECDIS in route planning and route monitoring mode, the display must be set in custom mode with spot soundings and isolated dangers. At all times, spot soundings must be displayed to a depth at least equal to the value of the Safety Contour.Additional layers of information must be added depending on the situation. For example, when the vessel is preparing to anchor submarine cables and pipelines, as well as any other applicable navigation hazards, are to be displayed on the screen.

The mariner must, however, bear in mind the risk associated with cluttering-up the screen unnecessarily. This can lead to ‘information overload’, particularly if the ECDIS display is also populated with radar overlay, ARPA and AIS information.

Masters are to prescribe their absolute minimum requirements for the information to be displayed on the ECDIS during each stage of the voyage. This list must be specific to the particular ECDIS equipment fitted onboard and should not be considered exhaustive; additional layers can be added to suit the prevailing circumstances. Form NAV 17 has been provided for this purpose, which is to be conspicuously posted on the Bridge.

Example

Scenario	Standard Display plus additional layers:	Other considerations:
Deep Sea	Spot Soundings to a depth of 2000m Details of isolated dangers	Max XTE 3704m (2nm)
Coastal	Spot Soundings to a depth of 100m Details of isolated dangers Ferry routes Details of aids to navigation Contents of cautionary notes	Max XTE 926m (0.5nm)
Anchoring	Spot Soundings to a depth of 50m Details of isolated dangers Submarine cables and pipelines Contents of cautionary notes	Max XTE 1852m (1nm)
Pilotage	Spot Soundings to a depth at least equal to the value of the Safety Contour Details of isolated dangers Contents of cautionary notes	Max XTE 185m (0.1nm)

• Colour mode setting: Colour Mode is to be set to 4 colours mode in order for the navigator to be able to distinguish the depth gradient of the waterway. The 2-colour mode does not allow the user to distinguish shallow patches which may be lost when navigating in the Safety contour area.