EDITOR'S NOTE: This is part two of a weekly series on computer-based navigation and electronic charting. For more about this series and why we wrote it, please see our Room 13 blog.
When the U.S. government released its electronic chart library for free in 2005, it was greeted by a cheer in the boating community. Charts would be available free for the taking by anyone with an Internet connection-who could complain?
But the reality is that many boaters still don't know where to start. They freeze when they see the dizzying list of thousands of charts, the cryptic file names, and the unfamiliar file extensions served up on the National Oceanic and Atmospheric Administration website. Do you need Chart 11448 or not? And who knows what BSB, KAP and PTC file extensions mean?
Begin by making a list of charts you need using the Catalog of Charts and Publications or on the NOAA website (below). With list in hand, you then enter the ChartServer database (above). Instructions guide you to select and order as many as 100 charts at a time, which are bundled for download in a single compressed folder.
It is problems like this that led Mad Mariner to launch its weekly series on navigation software and electronic charting. Throughout the rest of the year, we will cover what you need to set up a laptop-based electronic charting system, including hardware, software, external devices and charts.
In this installment, we look at how to take advantage of NOAA's system-yes, there is a system-including finding the charts you need, understanding the file names and content, and downloading them over the Internet.
Remember that in order to download and use NOAA charts you need a computer that is loaded with navigation software. Just like you cannot view a PDF document without Adobe's Acrobat Reader, you cannot view charts without navigation software from Nobeltec, Rose Point or some other vendor. There are more than a dozen to choose from, ranging from free minimally-featured options to richly-featured and highly configurable options costing thousands of dollars. (For a story on setting up a basic system, see link below).
FINDING WHAT YOU NEED
Unfortunately, NOAA's site does not have a "New England" button that intelligently downloads all the charts you need to cruise New England. Instead, you must do the work, consulting a NOAA Catalog of Charts & Publications, available for free at retail chart sellers or downloadable on the NOAA website. There are five editions: Atlantic Coast, Pacific Coast, Alaska, Great Lakes and Gulf Coast. These catalogs list all charts visually by their NOAA designator number. For example, the chart covering Martha's Vineyard to Block Island is Chart 13218. Cape Cod Canal and Approaches is Chart 13236. For complete chart coverage of New England you would need to look up all the charts, then download them. That's 107 chart folders, 209 charts, and 734 files!
Once you've identified the chart numbers you want to obtain, the next obstacle is the download itself. NOAA and the U.S. Army Corps of Engineers (USACE) both use web-enabled software, called ChartServer, which currently is limited to 100 charts per download. If you're on a pay-per-minute dial-up connection, think before you click. The New England example, with 209 charts and 734 files, involves a 501.5 megabyte download-half a gigabyte! With a common 56 Kbps dial-up connection, the download time would be more than 20 hours. Even with a high-speed DSL connection, it would still take more than two hours!
If you are willing to take the time or only want to download a handful of charts, use a download calculator to plan your time. An interactive calculator is available on the web at Intel's site (see link below). If downloading chart files seems cumbersome, you can purchase electronic charts in CD or DVD formats. These chart sets are relatively inexpensive, especially compared to the proprietary chips or cartridges used for chartplotters.
Interestingly, the price difference is not in the media-a plastic chip doesn't cost much more than a plastic disc-but in the source of the charts. Chip-stored charts are typically vector charts, which are rendered on screen from a database, rather than an image of a paper chart (those are called raster charts). Vector charts are not available yet for all regions through NOAA. The result is that you are not paying for the chip, but the manufacturer's cost of converting the original paper chart information into their proprietary vector format.
THE GREAT LOOP
Longer passages that cross maritime jurisdictions may require obtaining charts from several different government agencies. The popular "Great Loop" circling through the U.S. inland river system and the U.S. and Canadian canals and Great Lakes is a perfect example.
When downloading charts, it pays to keep track of download times, which can be hours. An online calculator like this can help you manage your download session time more effectively.
Many boaters are confused about electronic charting for the Great Loop-and their confusion is warranted. A Great Loop traveler needs to obtain charts from multiple agencies, both within and outside the U.S. Furthermore, some regions are available only in raster or only in vector format (while NOAA has a full catalog of raster charts, the agency is still creating vector charts for much of the country). An important rule of thumb is that vector charts are only available for "first-phase" areas, including ports and commercial connections. Fortunately, both the Great Lakes and the major inland river systems are considered commercial transit routes, and they were a priority in NOAA's program to create vector charts.
To understand the different sources and formats it's easiest to "armchair sail" the Great Loop circuit. Leaving Mobile, the Gulf of Mexico has free NOAA raster coverage. The Intracoastal Waterway, Chesapeake and Delaware Bays and the Atlantic Seaboard are also covered by NOAA, so free raster charts are available for their entire lengths. However, free vector charts are only available for areas deemed important to commercial traffic, such as major ports and coastal transit areas.
The Hudson River is also charted by NOAA, so the same rule applies: free raster charts for its entire length and free vector charts for the ports of New York and Albany. At Troy and the Waterford Locks, you enter the New York State Canal System and the so-called "Erie Canal." Although technically within the jurisdiction of the New York State Canal System, NOAA produces both paper charts and free raster charts for these waterways. However, future vector conversion, if deemed necessary, would be the responsibility of New York State.
Approaching Oswego, both raster and vector charts are available through NOAA. Beginning at the port of Oswego, the U.S. Great Lakes have complete raster and vector coverage. However, NOAA's charts, whether raster or vector, only cover U.S. waters. The only exceptions are small-scale charts that show a large region and may include portions of Canadian waters. The result is that the transit from Oswego to Chicago requires a mix of Canadian and NOAA charts.
The charts for the Canadian Great Lakes ports or canals are not free, either in raster or vector format. These charts must be purchased through authorized Canadian chart distributors. Recently, the Canadian Hydrographic Service (CHS) and Nautical Data International (NDI) ended their exclusive arrangement in a split similar to the one that took place in the United States between NOAA and Maptech in 2005, leading NOAA to offer its catalog of charts for free. Unfortunately, Canadian charts did not become available for free. Complete details of the CHS plan and a list of resellers are available online (see link below).
CORPS OF ENGINEERS
At the port of Chicago, you enter waters surveyed and charted by the U.S. Army Corps of Engineers (USACE). Corps charting efforts focus on shallow draft inland waters, meaning 14 feet or less at minimum maintained depth. The Corps distributes its charts only in vector format. Inland Electronic Navigation Charts, called IENCs, are available for free on the USACE website (see link below).
"The Illinois, Mississippi, Black Warrior, Tombigbee, and Mobile Rivers are all completed, comprising 90 percent of inland river system usage," said Anthony Niles, IENCs Project Manager. "Over time, we'll complete work on an additional 2,500 miles of lower traffic areas, with a current priority of the Missouri and upper Tennessee Rivers."
From Chicago to the Gulf of Mexico, vector charts are the only electronic chart option. There are no government raster charts for this stretch. Raster charts may be purchased, but with a caveat. Since these files are not government-produced, they are created by scanning outdated paper chart books, making them expensive and of questionable accuracy.
Fortunately, the Canadian Government, NOAA and the USACE work together using what is called an edge match system. For example, NOAA produces a chart to the head of Mobile Bay. Their cell for that region, "Mobile Bay Alabama," abuts the USACE chart running from Mile 0 to Mile 88 of the Tombigbee River, "Mobile Bay to East Bassetts Creek." The two charts are relatively seamless.
So, practically speaking, the biggest hurdle for Great Loopers and other long-distance cruisers is not the availability or alignment of electronic charts, but gathering them from multiple agencies and sources. It can be frustrating, but having charts for your entire trip in one laptop, where you can experiment with routes and anchorages, will make planning much easier. You can then take that laptop onboard, interface it with your instruments and have a sophisticated navigation system that is capable of making onboard life easier.
ACCURACY ISSUES
Despite the high-tech format, electronic charts are no more precise or accurate than a chart printed on paper. Because electronic charts use the same data transcribed from ink to bytes, they are only as accurate as the paper charts from which they were created.
Ironically, GPS technology has leapfrogged electronic chart accuracy, creating a potential mismatch of information. In the past, a fix using visual bearings, radar or Loran C gave an approximation of your position. This position estimate was good enough, particularly given the survey accuracy of the charts. Now you can get a GPS fix of your vessel's position to within three to five meters but, depending on the region, that position may be plotted on digital charts based on old survey data.
This "discrepancy of accuracy" between the chart image and your GPS fix can result in some strange screen displays. Boaters who zoom in and expect to see their vessel in more detail on their screen may experience the "ship on the pier" problem: your vessel icon appears on land, but you're in plenty of water. Remember, the image on the screen is only an electronic image of a paper chart-not the real world!
These differences in the accuracy of your position and your chart also underscore a common mistake when setting up waypoints and routes. Never place a waypoint too close to a charted navigation aid. The aid you see on your screen may not be exactly where you think it is.
USING ELECTRONIC CHARTS
So, how do you use electronic charts? In order for navigation software to display charts, you must tell it where the files are located. This task is called loading the chart and is separate from downloading the files and copying the charts to your hard drive. Charting applications typically use one of two systems for locating and recognizing charts: a smart folder system or a directory system.
Smart folder applications, such as Coastal Explorer or GPSNavX, have a designated folder on your hard drive. Any chart dropped into this folder is identified as a new chart. Each time you start the application, it scans that special folder, says, "Aha, those are the charts I have," and loads those charts as its database.
Directory-based applications, such as Marine ENC or MacENC, build a directory of charts and chart folders. You can have multiple charts in multiple folders, but you need to actively tell your software where those charts are located. Every application accomplishes this differently, and the process is usually described in detail in the application's manual or help files. The terminology varies, but the idea is the same: after the first set of charts that came with your software, you must direct it to the location of new chart files.
Smart folder applications are easier to manage, but they are not a panacea. Because everything is automated, they have a lot less flexibility and can cause problems.
A common problem with smart folders is the temptation to get sloppy with file hygiene. Becoming a "chart collector" and indiscriminately dropping chart files into this folder will severely bog down your laptop's performance. Furthermore, since every chart must first be read into the directory, a hefty smart folder will make your application significantly slower to open.
Directory-based applications require some attention to the manufacturer's operating instructions, but they are a precise chart management system that allows you to load and unload charts or regions as you need them. A little bit of time invested in learning your charting application's process will stop directory clutter and maintain optimal laptop performance.
Even if your laptop is a screaming demon, you should only load charts that you need. Selectively pre-load and unload regions as you travel. We have literally thousands of charts on our laptop, but rarely need access to more than a few hundred at a time.
Finally, although NOAA continually posts updated charts, these are targeted primarily for commercial vessels, which are required by law to carry the latest chart edition. Most recreational boaters are comfortable updating their entire chart catalog once a year or before a major cruise to a certain location.
NEXT WEEK: A Review of Free Navigation Software
Capt. Mark Doyle and Capt. Diana Doyle are authors of the Managing the Waterway cruising guide series, and their work has appeared in numerous publications. They also produce CDs and DVDs of NOAA and USACE charts.