Navigation that uses charts housed in an electronic device such as a computer, chart plotter or a GPS largely has replaced navigation with paper charts; handheld GPS units are commonplace, while chart book sales are declining.
Most boaters using electronic navigation systems depend on proprietary technology, such as Garmin's BlueChart system. Proprietary technology and charts have a variety of potential advantages, depending on the brand selected, but this type of system can be expensive; a new Garmin GPS76MAP CSx, for example, costs around $400, and a BlueChart data card likely will add another $150 or more to the total, depending on the coverage area selected.
But it's possible to get a basic marine navigation system for free, by downloading the free electronic charts available from the National Oceanic and Atmospheric Administration (NOAA), along with a free chart viewer or navigation program such as SeaClear. If a boater already has a notebook computer, especially a ruggedized computer designed for daylight viewing, this free system provides many of the same features as proprietary navigation systems.
NOAA offers two different types of digital charts -- vector and raster -- and it's important to understand the differences between the two before jumping into the marine electronic navigation world.
Raster Charts: Pictures of NOAA Charts
Downloaded raster charts look exactly like traditional NOAA paper charts, and with good reason: NOAA creates raster charts as digital pictures of paper charts. Marine store outlets that sell print-on-demand nautical charts use these same NOAA raster chart files to print their charts.
Most boaters who have used paper nautical charts will find that NOAA raster charts look very familiar and are simple to understand. The digital raster charts are geo-referenced, which means they can take GPS coordinates produced by a GPS sensor connected to a USB port and translate those coordinates into a position on the chart.
NOAA raster charts also have another significant advantage over older paper charts, vector charts, and proprietary marine navigation charts: NOAA updates them once a week with data from the U.S. Coast Guard's Local Notices to Mariners service.
Notices to Mariners includes important information about such potential navigational changes and hazards such as a moved or missing buoy, or a shifting channel. Having the most up-to-date chart, with Notices to Mariners data included, can mean the difference between a pleasant day's run and an expensive tow and repair bill after hitting a sand bar.
Raster Charts Have Some Disadvantages, Too
However, NOAA's raster charts have some disadvantages when they're used on a computer screen instead of on paper. Because they're digital images of a chart originally designed to be viewed on a large piece of paper (traditional paper charts range from three feet to five feet in length and can be up to 42 inches wide), boaters sometimes find it difficult to navigate when they can see only a small portion of the chart on a computer screen at one time.
In addition, because the charts are digital images, the depths and buoy light characteristics printed on the chart doesn't resize when a boater zooms in or zooms out, so the print becomes fuzzy. Often, at the point when it's possible to see about a third or half of the chart at once, the printing on the chart becomes unreadable. That means a boater plotting a course would need to zoom out to get a sense for the overall route, and then zoom back in repeatedly to see exactly where to navigate.
Vector Charts Include Tides, Currents
NOAA Electronic Navigation Charts (ENCs) aim to solve these problems while adding critical information that's not available on paper or raster charts.
ENCs are vector charts, designed to provide both real-time navigation information along with tide and current data. They're built out of digital data sets, and depending on the software used to display the charts, various information (such as tides, depths or buoy light characteristics) can be suppressed to unclutter the chart or selectively shown at different zoom levels and in various configurations.
NOAA vector charts don't look exactly like NOAA's paper charts; instead, they look like the computerized versions of marine charts found on many common marine mapping GPS and chart plotter systems. In fact, proprietary marine chart systems often use NOAA's free vector charts to create their chart products.
Because NOAA ENCs are electronic, they don't have the viewing disadvantages of raster charts; when the chart zooms in or out, the print resizes and remains legible.
However, NOAA does not update its ENCs as frequently as it updates its raster chart catalog, and the federal agency hasn't finished converting all its paper charts to the digital vector format. But it has converted charts for most major ports throughout the U.S. and many charts of waterways that connect these ports. Most boaters will find the charts they need in ENC format.
RWC101
Jane Anderson - Jane M. Anderson spends as much time as possible on the water, working and sailing on boats. She grew up sailing Sunfish and Rhodes 19s on ...
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