Owning A Boat: Equipment
GPS Overview: The Sky’s the Limit
What
is GPS?
GPS,
or Global Positioning System, is a satellite-based navigation system developed
by the U.S. Department of Defense to provide a consistent, accurate method
of simplifying navigation. It was originally designed for the military, however,
it provides both commercial and recreational users 24 hour, worldwide navigation
coverage with an accuracy between 15 to 30 feet. Like any other method
of navigation, you should not rely solely on your GPS. You should
use every method of navigation available and compare the results to make sure
that you are where you think you are.
What
are the Advantages of GPS Navigation?
For
centuries, mariners have been searching for an accurate method of traveling
the world's waterways. From celestial navigation to lorans and SatNav, each
system has had its problems with weather, range and reliability.
GPS
takes navigation to a higher level by providing accurate position and course
information, anywhere in the world, regardless of the weather or your proximity
to land. The accuracy and coverage of GPS navigation can help make your boating
safer, smarter and more efficient wherever you may travel.
The
GPS is a powerful tool. To better understand its operation and capabilities,
it may be helpful to review the basic terms and concepts explained below.
Navigation
is the process of traveling from one place to another and knowing where you
are in relation to your desired course.
Position
is an exact, unique location based on a geographic coordinate system. Marine
navigation is based on the latitude/longitude coordinate system.
Meridians
of longitude are a set of imaginary
circles around the earth that pass through the north and south poles. Longitude
describes position in terms of how many degrees it is east or west of the
Prime Meridian (0* Longitude which runs through Greenwich England).
Parallels
of latitude are another set of imaginary
circles that are perpendicular to the earth's polar axis. Latitude describes
position in terms of how many degrees it is north or south of the equator
(0* Latitude).
A
waypoint
marks an exact position fix so it can be recalled for future use. The GPS
lets you mark waypoints electronically, without physical landmarks.
Bearing
is a compass direction to a particular destination (waypoint) from your present
position.
Track
is a compass direction representing your course over ground or course made
good.
How
Does GPS Work?
GPS
Navigation uses orbiting satellite signals to determine your position. These
satellites continually send out radio signals containing precise position
and time information back to earth. By knowing the position of 3, 4 or more
of these satellites and calculating various time differences between the transmitted
signals, your GPS receiver can determine its present position anywhere on
earth. Once underway, your GPS continually updates your position and provides
speed and track information.
What
information do I get from a GPS?
Various
manufacturers make GPS's and some have more features than others but all give
basically the same information. Almost all of them have graphic displays and
some even have a cartographic feature which allows you to see your location
on an electronic chart. If you are going for a fixed mounted GPS rather than
a handheld portable, I would vote for a model that does support electronic
charts. This provides yet another way of checking your position, especially
if you are in site of land or an object on the chart.
You
should expect your GPS to accept waypoints (where you want to go) and routes
(a series of waypoints leading to your final destination). Once you have input
a waypoint the GPS will calculate your current position and give you, at minimum,
the following information:
- A course
to steer to the waypoint (continually updated)
- The distance
to the waypoint (continually updated)
- Once underway,
your speed (continually updated)
- The time
it will take to get to the waypoint at your current speed (continually
updated)
- Turn, Steer
or Off-Course Error -- the GPS should tell you when you are off course
and what direction to turn to get back on course.
- Various
alarms should be available such as:
- an
arrival alarm which sounds when approaching a waypoint
- a proximity
alarm which sounds when you come within a preset distance of any of
several waypoints, regardless of whether they are your destination
- an
anchor alarm which sounds when you travel more than a preset distance
from a waypoint
- an
off-course alarm which sounds whenever you are exceeding a preset
distance from your intended course
With
all this information could I share it with other electronics?
The
ability of a GPS to share information with an autopilot, radar, or plotter
adds to the utility and power of the device. Just think of having the ability
to feed your autopilot information on a multi-leg route to a favorite diving
spot and having your boat guide itself safely there, leaving you free to ready
the equipment, monitor the radar, and stand watch.
Should
I buy one?
It
is my opinion that GPS receivers are like your American Express card (don't
leave home without it). You can get a portable GPS receiver for under $200.00
and fixed mounted models start at under $300.00 and can go up from there if
you get into electronic charts. Is it worth $200.00 to know your position
in any weather, anywhere on earth, within just a few feet? Like the computer
revolution, the GPS revolution is a great example of increasing features,
increasing user friendliness, and decreasing costs.
Once
again: You should never rely on only one method of navigation, especially
if you will be out of sight of land.
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