EDITOR'S NOTE: Today begins 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.

Armchair travel has always been about imagination, but armchair navigation these days can actually get you somewhere, just fire up your laptop and go.

Take, for example, a cruise up the Potomac River in Washington DC. Type "Washington Channel" into a search field and a full-color nautical chart appears on your screen. You can see markers, marinas and depths as you scroll upriver setting waypoints. Mouse-click on the bridges and windows pop up showing the vertical clearance for each. Click again and you might see a satellite image of the Georgetown waterfront. Scroll to the anchorage at Three Sisters, zoom in and mark your destination. The entire trip can be planned without unfurling a chart or setting foot on the boat.

This is no futuristic scenario, it is navigation software today.

With large databases of electronic charts widely available, often for free, and more than a dozen vendors selling sophisticated programs to make use of them, computer-based navigation has never been more accessible. Boaters can gather more quality information and plan routes with more precision than ever before, all from a laptop that can be taken anywhere.The Georgetown waterfront in Washington DC, as seen using free Coastal Explorer trial software and a free NOAA raster chart. Both were downloaded easily.

Yet creating a computer-based system can still be frustrating. There are a bewildering range of products available that vary widely in quality and cost. There is also little about electronic charting that could be described as plug-and-play. Loading the software, configuring it to speak to the instruments on your boat and then coaxing it to deliver on its promises can leave even tech-savvy boaters scratching their heads.

Furthermore, navigation software is one area in which good advice can be hard to find. What worked well on your friend's catamaran may not be well suited to your trawler. The system your electronics dealer raves about may be too complicated for your tastes, or too limited. And buying a well-known brand name or paying a bit more does not necessarily yield a better product.

To help sort it all out, Mad Mariner is launching a weekly series dedicated to eliminating some of the mystery. Throughout the rest of the year, we will look at what you need to set up a laptop-based electronic charting system, including hardware, software, external devices and charts.

We will explain how electronic charting works, decipher some of the jargon and review the process of obtaining charts on the Internet. We will also explore the software used to work with these charts, including a full-length test and evaluation of every major product on the market. The result, we hope, will be a definitive resource that can help you make decisions about how to best harness the powerful resources now available.

FLEXIBLE AND FEATURE RICH

Getting started in computer-based navigation is far less confusing if you take the time to understand what is available in the marketplace, how those products are evolving and what you need on your boat to take advantage of them. In short, the "for dummies" approach works well here.

For starters, electronic charting is nothing new. Many of us have chart plotters onboard made by Garmin, Raymarine, Furuno or other manufacturers. These units draw upon charts, often provided by companies like C-Map or Navionics, that usually reside on a memory chip or an integral hard drive. The resulting system is a good one, time tested, easy to use and more than sufficient for many boaters.

Yet a new breed of system based on the personal computer has evolved in the last decade that is flexible, feature rich and often far cheaper than the boxes set in the dashboard. A standard laptop fitted with navigation software and a database of charts can replicate features found only on the most expensive in-dash units, and it can make navigation far easier. It may not replace your chart plotter, but it can be a powerful augmentation.

The obvious advantage of a laptop-based system is you can, quite literally, take it anywhere. You have the ultimate in portability, bringing your charts with you from helm to saloon to home. We even bring our laptop from boat to boat for delivery work or trading waypoints with fellow captains and cruisers.

Another primary advantage is that a computer-based system can make planning far easier. You can locate marinas, set waypoints, pre-build navigation routes and annotate your charts in a comfortable environment. Most computer screens are larger and have better resolution and color than their in-dash cousins. Most navigation software has the familiar click-through environment we are used to on the Internet. And you have the added benefit of a familiar keyboard and mouse. The result is that you are apt to spend more time navigating, and therefore be better prepared on departure day.

It is also easier to maintain navigation information because data entry can be easier. Laptop charting lets you visually select waypoint locations using your cursor instead of typing latitude and longitude numbers, an error-ridden process even for the most meticulous typist.

Many laptop-based systems have features that cannot be found on hard-wired installations, such as a ship's log, fuel calculator, maintenance schedule and vessel inventory. Add an Internet connection and real-time reports on weather and tides become available. Tie the computer into your boat's instrumentation and you can see the depth in your current location and track your true course. Medium-priced navigation software gives you the ability to call up aerial or satellite pictures and more expensive packages offer bathymetric charts, which show the topography of the sea floor.

Perhaps the most appealing aspect of a computer-based system is that it is flexible, with a wide range of options for boaters with different skills and budgets. Using a laptop you already have, a free software application and a set of free charts, you can setup a basic system at virtually no cost. You can also spend thousands of dollars on a dedicated machine, spend another thousand on software and rig a network to replace your boat's primary navigation system.

And there is much in between.

BUILDING A SYSTEM

All computer-based navigation systems have four main components: a personal computer (laptop or desktop), external sensors such as a GPS, a database of charts and navigation software to read them.

Many boaters agonize over the laptop, but this is probably unnecessary. If you have a fairly recent machine, it may do just fine. If you plan to buy one, the attributes you look for in a good family computer, speed and storage, will apply here as well. There are companies that sell "hardened" or "marinized" computers, but they are generally not necessary. A machine purchased from any number of brand-name vendors will work just fine.

Any computer, PC or Macintosh, that can run graphic-intensive games or handle large photos can display and manipulate large charts. Just remember that the screens are not easily viewed in daylight, and the machines are not waterproof. A reasonable setup would include at least one gigabyte of RAM (two gigabytes is better), an 80 gigabyte hard drive, a high-end graphics card, a screen that is 15 inches or larger and a DVD-drive. Because chart compilations are extremely large, more vendors are producing single DVDs rather than CD-sets and a DVD drive is highly recommended.

Also in the hardware department are external sensors, which link data from your boat to your laptop. There is all kinds of "Star Wars" potential here, including external sensors for sonar, radar and even video cameras to monitor your engine from the helm. But the most common application is a GPS sensor that costs about $100, connects to your laptop through its USB port and can display your boat's position as an icon moving over a chart.

Don't overlook the seemingly obvious fact that you must have navigation software to view electronic charts. Just as you can't open a PDF file without Adobe's Acrobat Reader and you can't open a DOC file without Microsoft Word, the same logic applies to an electronic chart: you can't open a BSB file without one of the navigation applications designed to display BSB files.

Navigation software comes in many flavors and this series will test and review each of the major products on the market in coming weeks. For now, we'll simply say that there are a wide variety of packages in many price ranges, including software from Nobeltec, Maptech, Raymarine, Rose Point and other companies, and that some of these manufacturers offer a trial version on their website. Trial versions, or demoware, are either time limited or have certain functions disabled, but they are a great way to test out products before you spend money. Another option is free software, such as CARIS Easy View and SeaClear II.

THE STORY ON FREE CHARTS

The last component is the charts themselves, and here we will drill down a bit. Changes in the availability and price of nautical charts have fueled the drive toward computer-based navigation, and understanding what is available and how it is evolving is essential if you plan to setup a system.

For starters, the data that we see on charts for U.S. waters is almost universally provided by the federal government, specifically the National Oceanic and Atmospheric Administration, known as NOAA (pronounced no-uh). You may be looking at a chart product purchased from a company, but the majority of the data on that chart was probably provided by NOAA. The reason is simple: the federal government is the only organization that has the resources to collect that much information and keep it reasonably current.

NOAA has made paper charts available for decades, but it wasn't until 1995 that it began offering charts in digital form. It did so through a partnership with Maptech Inc., which sold the charts in a trademarked format known as "BSB." Other companies had competing products, but Maptech was the only official supplier of NOAA charts.

One criticism of the arrangement is that the charts were relatively expensive, causing boaters to keep the same charts for years in order to avoid spending money for an update. When NOAA's agreement with Maptech expired in 2005, the agency made its catalog of roughly 1,000 charts covering all U.S. waters available for free via download from its website, and took other steps to get accurate digital charts into the hands of boaters. (For a story on how free charts came about, see link below).

Raster charts are scanned images of paper charts. They are popular because of their familiar appearance, but zooming in tight is problematic because the chart is a static image. Zoomed objects are subject to overscale and pixelization, as shown.

With free charts online, why isn't every boater carrying the latest up-to-date charts in electronic format? That is NOAA's goal, but a few hurdles remain before computer-based navigation becomes universal.

RASTER VERSUS VECTOR

The format of electronic charts, namely raster or vector,is an important distinction to understand, because it will affect what you see on your laptop screen and, more importantly, how you use the charts on the water.

Raster Navigational Charts, often called RNCs, are scanned digital images of NOAA paper charts. Each chart is basically a color copy comprised of millions of "picture elements" or pixels, saved as a large file.

Vector charts, known as Electronic Navigational Charts or ENCs, are a database that contains objects,points, lines, polygons, symbols and other data, that correspond to the features on a chart. Each data point is located by its latitude and longitude, and is linked to a list of attributes. For example, a navigational aid may be associated with attributes such as location, number, height and light color.

If you understand the fundamental difference between these formats, you may already foresee the implications for file size. In one case the chart is an image comprised of millions of saved pixels. In the other case the chart is a database of navigational objects linked to a chart position. Because raster charts are scanned pictures, and every pixel on the chart must be represented in terms of color and intensity, the files are huge. Vector charts are a database rather than an image, so the information is compressed into much smaller files, taking up less space on your hard drive.

Raster and vector charts look very different on your laptop screen. Raster charts look like traditional NOAA paper charts. Many boaters like raster charts for the simple reason that the chart "looks right." In contrast, vector charts only show land forms and some depths. In fact, they are so sparse that some boaters mistakenly think information is missing.

It's all there. Vector charts are simply displayed in layers. This format reduces chart clutter and lets you select only the information you'd like to view, which is very handy in large harbors and other areas where there is much to note. Simply click on the symbol for an object on the chart, such as the small square icon denoting a marina, and a data window appears with detailed information about that facility.

Because raster charts are scanned images, you cannot "zoom in" to see more detail. Zooming the display past the accuracy of the digitized image, called overscale, results in an unreadable mosaic of colored pixels. Vector charts, because they are created on-the-fly using a database, allow you to zoom in to see more detail.

A similar distinction occurs when you attempt to rotate electronic charts, as you might do to display a chart "course up." Raster charts are large image files and do not rotate quickly. Even worse, the text is fixed and therefore rotates with the image, giving you a course-up chart with depths and other information displayed upside-down or sideways. In contrast, vector charts have the ability to create a display independent of orientation, with text data on a separate layer. Rotating displays are not a problem.

Finally, the most important implication of raster versus vector chart formats lies in their "intelligence." A depth contour of 60 on a raster chart is simply a collection of black pixels to create the numeric characters six and zero. That same depth contour on a vector chart is a value in a database linked to its position in latitude and longitude. Because vector charts are databases of navigation items, they can be intelligently linked to navigation software, which can compute distances or sound an alarm if the vessel crosses a depth contour (say 60 feet).

Raster charts are only pictures, so navigation software is unable to differentiate between a buoy pixel or a water pixel.

FAMILIARITY AND AVAILABILITY

Although vector charts seemingly have the technological advantage, raster charts currently win on two counts: familiarity and availability.

Because they look familiar, raster charts are much easier to use for planning and general chart viewing. Most boaters still have trouble assimilating the sparse display of a vector-format chart. Fortunately, there is an effort underway to standardize paper chart symbols. When complete, there may be less visual discrepancy between paper and electronic chart formats.

Vector charts are based on a database and are organized in layers, that can be quickly drawn at any scale. They are becoming popular for their uncluttered appearance and intelligent storage and display of information. Clicking on a bridge or navigation aid displays a window, as shown.

Raster charts are also more plentiful. Because converting paper charts to raster format is infinitely easier than creating a vector database, a complete U.S. raster catalog is already available through NOAA for free. But only about 60 percent of NOAA's projected chart cells are available in vector format. Creating a vector database of all chart features is an enormous project and the priority for conversion is driven by the "professional navigator" and commercial ship traffic.

In 2001, NOAA initially identified 40 major ports for completion by 2003. After these were done, another 100 or so ports were identified for conversion. NOAA's priority is to begin with major ports, followed by the seaward connections between these ports for commercial shipping traffic. For example, the Intracoastal Waterway between the commercial ports of Norfolk and Charleston is not a priority. Instead, the seaward connection between these two ports, including Cape Henry and Cape Hatteras, is a priority. So far, NOAA has completed about 600 of its roughly 1,000 projected vector charts.

This huge task is hampered by government budgets and further slowed by the demands of simultaneously maintaining and updating an increasingly larger chart library. Alexandra Heliotis, Deputy Chief of NOAA's Marine Chart Division, points out that an average year produces 5,900 individual updates that result in corrections to 16,000 chart products.

Still, there are few who would argue with the idea that the vector format is the future of electronic charting. The files are smaller, more intelligent and make it easier to incorporate frequent updates. Oddly enough, NOAA's long-term vision is the reverse of what it has been doing for decades: the agency wants to print paper charts from an accurate and up-to-date vector database.

NEXT WEEK: How to locate, load and catalog electronic charts.

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.