This portion of an electronic navigational chart shows mud and clay areas, and an entrance point. ENCs are now available from NOS's Office of Coast Survey for download.

Mariners now have a choice about the types of navigational tools they use. NOS’s Office of Coast Survey (OCS) recently offered electronic navigational charts (ENCs) as official navigation products for mariners. The ENCs, which had been in provisional use for the last two years, are the next generation of nautical charts. They improve on traditional paper (raster) nautical charts and support all types of marine navigation. Such integration and automation of navigational tools will help reduce human error on the seas.

What They Are

Often called “smart charts,” ENCs provide the nautical data that mariners need, plus vector map features and hydrographic data. They also include electronic compatibility features that paper charts lack. For instance, a mariner can integrate global positioning system (GPS) data—which tells a mariner his or her precise latitude and longitude—with ENC data. The mariner can also integrate data from geographic information systems (GIS), real-time tide and current data, and wind data to enhance the capabilities of the ENC. This information is especially important to large commercial vessels that must navigate through narrow areas.

ENCs were developed using several sources. OCS used NOAA hydrographic survey data; large-scale paper charts; U.S. Army Corps of Engineers’ surveys, drawings and permits; Notices to Mariners; and other primary sources to compile the charts.

Aerial photographs like this one are used to develop ENCs. Other tools used include hydrographic survey data, drawings and permits, and paper nautical charts.

How They Work

ENCs are structured and formatted in the International Hydrographic Organization S-57 standard, which is a nonproprietary, publicly available format. This means that anyone with an electronic charting system, such as the popular Electronic Chart Display and Information System, can use ENCs. The navigation system software uses the ENC data to draw an electronic display resembling a traditional nautical chart. Specific and unique navigational features are highlighted on the screen display with an identifying mark such as a color or shape.

These charts incorporate GPS and GIS information to create a fuller, more accurate picture of the marine environment. Thus, a vessel using NOAA ENCs can detect an obstruction ahead and check planned travel routes to avoid crossing hazardous areas. The system displays warnings and regulations that pertain to areas in which a vessel transits, and can sound an alarm if the vessel’s projected course veers too close to a dangerous feature.

In addition, a mariner can control the ENC display by turning features on and off, depending on the needs of the vessel. This helps to eliminate clutter on the computer screen, allowing the mariner to see only what is essential. Users also can query the ENC data to obtain specific information.

In addition to navigational purposes, ENCs can be used as a background layer for GIS applications. They also are useful adjuncts to vessel traffic observation systems, which monitor ship movements in rivers, harbors and bays.

Harbors like this one are becoming increasingly populated and harder to navigate, especially for larger commercial vessels. ENCs will help vessels navigate these areas safely.

How to Get Them

Mariners can download the new ENCs free of charge via OCS’s online database. Many mariners are already doing so. Between July 2001, when they were first introduced online provisionally, and May 2003, more than 500,000 ENCs were downloaded. Users continue to access ENCs at brisk rates.

Two versions are available. Version 2 ENCs are the official products and include all the information contained on their corresponding paper charts, with a few land-based exceptions. These official ENCs will be updated regularly. Older versions—Version 1 ENCs—were essentially test products and do not contain complete information. Now that Version 2 charts are available, Version 1 charts will be revised and made available on an ongoing basis.