Electronic charting and navigation
brings challenges and opportunities
to the maritime community.
Automatic Radar Plotting Aids (ARPA) display a ship's position and other nearby vessels, helping avoid collision in selecting a course.
And Long Range Tracking and Identification (LRTI) ensures a thorough international tracking system for ships around the world.
Onboard status sensors provide even more capabilities.
Rudder Angle Indicators (RAI) provide data to the bridge to help control rate of turn.
And Voyage Data Recorders (VDR) continuously capture vital information related to the operation of a ship.
Some technology advances are accessible to recreational boaters, particularly those operating larger vessels.
The Automatic Identification System (AIS) helps to pinpoint locations and other navigational statistics of other vessels.
Auto Pilot combines hydraulic, mechanical, and electrical systems to control steering from the navigation bridge.
And Radar helps determine the distance of a boat from land, other vessels, or floating objects in the water.
One innovation has become nearly ubiquitously available to recreational boaters:
The Global Positioning System (GPS) -- a navigation system developed by the U.S. Department of Defense.
GPS provides continuous, all-weather, three-dimensional location data.
GPS receivers display their current position accurate within fifteen-to-one hundred yards with the help of satellites orbiting the earth.
They typically also show local time,
direction of travel,
and speed over ground.
GPS is used by aviators,
mariners,
surveyors,
motor vehicle drivers,
bicyclists,
hikers, and others.
GPS receivers with special features for boating --
like chart-plotting --
are available in handheld units as well as fixed-mount installations.
Chart-plotting is important to recreational boaters because,
unlike GPS for automobiles,
there are no established roads, streets, or routes to follow.
Typically an electronic chart is embedded in the receiver
to synchronize and display in the background
under the boat's position icon.
To appreciate the value of GPS for boating, begin with latitude and longitude.
Latitude, measured as an angle from the center of the earth,
defines position in the north or south direction.
Longitude, measured as an angle from a meridian passing through Greenwich, England,
defines position in the east or west direction.
Every point on earth has a unique latitude and longitude address,
and this is displayed on a GPS.
These geographic coordinates can be selected to serve as waypoints,
which are used extensively in electronic navigation.
Waypoints can create boundaries between voyage segments
to mark turn points, destinations, and aids to navigation or ATONs.
GPS receivers enable waypoints to be entered and stored as user-created abbreviations
corresponding to their lat/long units.
Waypoints don't have to be located in the water --
a lighthouse can be set as a waypoint, so you'll know where and when to look for it.
Waypoints can also be used to mark hazards to navigation --
areas to avoid, as well as areas to visit.
A sequence of waypoints can be constructed to define a planned route,
and many GPS receivers can store routes as well as waypoints.
Start by plotting waypoints for your voyage on a large-scale paper chart.
Measure the distance and bearing between waypoints.
GPS receivers will accept waypoint definitions and descriptions.
They'll also show track and distance to any other selected waypoint.
Where possible, select waypoints with rounded-off coordinates to minimize transcription errors.
Verify by plotting on the chart that your voyage legs are in safe water before entering them into your GPS.
Practice using your GPS during ideal conditions to ensure familiarity with controls and procedures.
When a GPS receiver is booting-up,
bars in its display show the number and, by their height, the signal quality from satellites currently visible.
Most receivers have several display modes,
or pages,
such as lat/long of present position,
waypoint in use,
bearing,
and distance.
GPS receivers show heading -- the direction in which your vessel's bow is pointed;
course made good, the direction traveled from one fix to another;
distance made good, the same in terms of distance;
bearing, the horizontal direction from one point to another measured relative to true or magnetic north;
and track, the intended path of your vessel over the earth's surface, typically shown as a line between waypoints.
Distance off the selected track is shown as cross-track error.
Time-to-go and estimated-time-of-arrival at the next waypoint are also shown.
Sophisticated receivers have other functions including graphic displays and various alarms.
When underway, write down positions every few minutes to have your last known position in the event of receiver failure.
Periodically verify your GPS position using other methods, and check for malfunctions.
At each waypoint, check receiver indication of bearing and distance against those measured on your chart.
With practice, you'll find that GPS can be a valuable aid to recreational vessel navigation.