Humans have traveled the oceans for eons. Unlike roads and paths, the water is a vast and open place, where finding your way entails creativity and knowledge. For centuries, we've been relying on star charts, compasses, and latitude and longitude numbers to navigate the seas and waterways. These techniques have constantly been refined and updated, but the main premise has remained intact.

All of this has changed in the most revolutionary way when the GPS technology has entered the scene. Sailors were now able to pinpoint their location with astounding accuracy, and figure out their way through the waters with unparalleled efficiency.

A good GPS unit has since turned into the norm. And for good reason. A marine GPS unit is an indispensable piece of equipment preventing boaters from getting lost at sea and assisting rescue teams in locating vessels in distress.

As the technology improved, so have the devices. Currently, the market offers quite a variety of units and devices. The following paragraphs will be outlining the most common and detailing their contents and features, thus enabling you to get a better understanding of what they have to offer thereby assisting you in choosing the one that's right for you and suits your needs best.

When shopping for your marine GPS device, you'll find several different types, with each of them offering different features and capabilities. Most of the common types -- Chartplotters, fishfinder combos, and standalone navigators -- have the necessary navigation capabilities, while some of them will combine other functions to enhance their performance and utility.

Chartplotters. A Chartplotter is a device that integrates GPS data with an electronic navigational chart (ENC). The chartplotter displays the ENC along with the position, heading and speed of the ship, and may display additional information from radar, automatic information systems (AIS), or other sensors. Like you'd expect of a typical GPS unit, a chartplotter features a display and comes equipped with an antenna, which is installed on top of the boat. 

The antenna picks up GPS signals and transmit latitude and longitude numbers to the display unit. A graphic will then display on the screen, indicating the boat's location with the precision of a few feet. Additional relevant data, including depth contours, surrounding buoys, potential hazards, and land masses, is also included on the display screen.

Most chartplotters offer the option for creating waypoints and routes. Some Chartplotters come with an option for being connected to a computer, or even with their own keyboard, which extends the functionality and ease of use.

Fishfinder Combos.

Contrary to what the title implies, the use of Fishfinders is not exclusive for fishermen, and "civilian" sailors can put a chartplotter-fishfinder combo to good use. With the integration of a sounder supplying depth and bottom composition information, the chartplotter-fishfinder combo turns into a more advanced, 3D-like navigator that provides even more information, in greater depths.

While these devices typically come with rather small screens, which is somewhat of a limitation, the combo units do offer an affordable, functional, and practical alternative to single-function GPS devices.

Standalone Navigators.

This section deals with your typical GPS navigation system, which has become so commonplace among vehicles, drivers, and even walkers, which utilize the Global Positioning Service provided by a host of Apps designed for smartphones.

Chances are that your boat has already been outfit with a standard GPS unit, as a large number of them come with permanently installed navigation systems. But yours isn't, a standalone navigation unit would make do -- even if only for the sake of serving as a backup in case, you know, stuff happens.

Smartphone-size with an App-lookalike GPS is also a viable option. A decent one will be able to accurately track your boat's position and location, as well providing speed and course information. Keep in mind that those handheld GPS units should be meant for marine use, which is to say they should be water-resistant and protected against the elements. Some of these units may also provide lunar, solar, and tidal data, but with their small screen, handheld units generally lack the ability to display easy-to-read charts.

In summary, your choice of GPS device comes down to what you're trying to use it for and how well versed you are in the functions and content provided by the various devices. Sailing on a local lake or other small bodies of water for light recreational purposes doesn't require anything more advanced than a typical marine GPS with the basic functions, while a seasoned fisherman should opt for a sophisticated multi-functional device, complete with a fishfinder, that will provide electronic charting, weather reporting, and alerts for dangers such as shallow reefs.

Further reading:

http://www.brighthub.com/electronics/gps/articles/46957.aspx

http://sailing.about.com/od/navigationseamanship/a/basicchartplotter.htm