ENC

An Introduction, Definition and Details:

Electronic Navigational Charts are vector charts that conform to IHO S57 specifications. They are compiled from a database of individual items of digitized chart data which can be displayed as seamless chart. ENC’s are far superior to Paper or Raster Charts, and are intelligent vector database that can be queried for information for displaying selected feature, object or layer containing the navigational information. The systems using them can be programmed to give warning of impending danger in relation to charted information, and the vessel’s position and movement.

The official definition of ENC is that it is a database, standardized as to content, structure and format, issued for use on an ECDIS, on the authority of government –authorized hydrographic offices. The ENC contains all chart information necessary for safe navigation, and may in fact contain supplementary information in addition to that contained in the paper chart (for example sailing directions) which may be considered necessary for safe navigation. Any other vector data is unofficial and does not meet chart carriage requirements.

All ENC’s are based on the World Geodetic System 84 (WGS84), and are organized in so called Cells.

The cells are allocated to defined scale ranges with a different degree of generalization or usage bands. Each usage band has a special number, and depending on the navigational situation, the following cells are available:

There are two types of electronic charts: Raster and Vector.

A Raster chart is a scanned and passive image of a paper chart, whereas a vector chart corresponds to a digital analysis by object (points, lines, areas etc.)

• Evolution of ENC’s
• What is an official ENC?
• ENC’s - Its distinct advantages in navigation
• Equipments required for a vessel to install and implement ENCs
• The main advantages of ECDIS
• ECDIS components

Evolution of ENC’s

1. The concept of digital Chart was evolved over a period of twenty years since 1970’s.
2. Initial efforts were focused on generating charts using computers and plotters for paper chart production.
3. 1980’s saw an enhancement of graphic capabilities which provided impetus to develop shipboard systems for use of digital charts for navigation.
4. Due to a variety of formats and systems of navigation proliferating ships, regulatory bodies such as IMO and IHO that set standard for sea going vessels, set up specific committees to look in to standardizing such systems.
5. IHO set up the Committee of Electronic Chart (COE) to interact with various Hydrographic Offices and the user community, to finalize a standard now known as IHO S57, Edn.3.1.1
6. Simultaneously IMO looked into various aspects of shipboard systems for displaying Digital Charts and went on to define the standard for such systems in collaboration with IEC, enabling equipment manufacturers to design systems in compliance with IMO specification for use onboard ships.
7. The IHO standard defines the database for use on such systems.

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What is an official ENC?

ENC’s are charts issued by or on authority of a government authorized hydrographic office, or other relevant government institution, and may be used to fulfill carriage requirements, provided they are kept up to date.

The salient features being:

1. ENC content is based on source data or official charts of the responsible hydrographic office.
2. ENC’s are compiled and coded according to international standards.
3. ENC’s are referred to World Geodetic System 1984 Datum.
4. ENC content is the responsibility of the issuing hydrographic office.
5. ENC’s are issued only by the responsible hydrographic office, and,
6. ENC’s are regularly updated with official update information distributed digitally.
   

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ENC’s - Its distinct advantages in navigation:

ENC contains all chart information necessary for safe navigation plus supplementary information in addition to that contained in the paper chart for a safe navigation. Its distinct advantages include:

1. Increased Safety at Sea Oeration
2. Immediate and accurate updating
3. Electronic overlays
4. Radar Integration
5. Immediate chart access
6. OOW Assistance in close quarters
7. Real time positioning
8. Automatic Data Logging.

ENC’s automate the process of integrating real-time positions with chart displays that effectively allows the navigator to continuously assess the position and safety of the vessel.

The use of ENC’s also allows the integration of other operational data, such as ship’s course and speed, depth soundings and radar data into the display. Further they allow automation of alarm systems to alert the navigator to potentially dangerous situations weel in adavance of the disaster.

The information on Chart can be linked to specific points. It allows the user to display the information that is necessary for the ship’s current mission.

And finally it conveys real time information of all chart hydrographic objects or entities.

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Equipments required for a vessel to install and implement ENCs

A navigational electronic chart system is a general term for all electronic equipment that is capable of displaying a vessel’s position on a chart image on a screen.

There are two classes of navigational electronic chart systems: the first is an Electronic Chart Display and Information System (ECDIS), which meets IMO / SOLAS chart carriage requirements; the second is and Electronic Chart System (ECS) which can be used to assist navigation, but does not meet IMO / SOLAS Chart carriage requirements.

Meeting Carriage Requirements:

Only a type approved ECDIS operating with up to date ENC’s and with appropriate back up may be used to replace all paper charts on a vessel. Where ENCs are not yet available, IMO regulations allow Flag States to authorize the use of RNCs (together with an appropriate folio of paper charts), and that in all other cases the vessel must carry all paper charts necessary for its intended voyage.

From the regulatory perspective, the most important statement about the legal status of ECDIS is contained in the amended Chapter V of the SOLAS Convention set into force on July 1 2002, and IMO ECDIS Performance standards (IMO Resolution 19) - “Carriage Requirements for ship borne navigational systems and equipment”

However, in order to replace paper charts, such systems must fulfill considerable technical requirements laid down in ECDIS Performance standards:

• The chart data in use must be official ENCs where they are available;
• The graphic display on the screen must meet the requisite equipment – independent specification; and
• The equipment must support the full range of navigational functions that can be performed on traditional paper charts.

Equipment requirements:

• If the ship is using an ECDIS, then it must meet IMO/SOLAS chart carriage requirements.
• The range of other interface with ECDIS are ARPA, Radar, DGPS, NAVTEX, AIS and GYRO.

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The main advantages of ECDIS:

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ECDIS components:

1. Computer Processor and Network
2. Chart Data Base
3. System Display
4. Planning Station
5. Control System
6. Sensors

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