Combination Marine ChartPlotter and Car Navigator
By Richard S. Wilson
Release 2,  May 30, 2004


The Garmin GPS276C is a nice evolutionary step in GPS technology for the Marine user.  If you would like to have a GPS receiver for automotive use and another for marine navigation, you can get both with the GPSmap 276C.  You can switch modes easily and have separate setups for each.  Set up the page layouts and parameters for your car trip: data fields, statute miles for distance, speed in MPH, page sequence, etc.  Then switch to marine mode and set it up for different data fields, nautical miles, speed in knots, more pages, etc.  When you switch back and forth the unit will retain the options you selected for each mode.  Even the maps will switch from the road map to the marine map.   It really is having two units in one.


The GPSmap 276C is a 12 channel marine chartplotter/car navigator unit which includes WAAS capability (Wide Area Augmentation System).  It is housed in a black case about 5 3/4 inches wide by 3 1/2 inches high.  There is a removable mounting bracket included which increases the total width to about 6 1/2 inches.  The unit has a 256 color TFT display that is very readable in direct sunlight.  This is unlike the GPSmap 176C which practically loses its visibility in sunlight.  The viewing screen is about 3 1/8 wide by 2 1/4 high (3 7/8 diagonal).  The G276C supports the autorouting feature found in many Garmin MapSource products, and in automotive mode will create a route following the roads, rather than a series of straight lines.  We were disappointed to find that the GPS-276C uses the older Garmin memory card.  Though a 256 megabyte (maximum size)  Garmin memory card is now available,  these are considerably more expensive "per megabyte" than the CF memory card used in the new StreetPilot 2610 series.

The packaged unit comes with a rechargeable Lithium battery, mounting bracket to fix the unit to a solid surface, data cable for programming from a computer USB port, a power and USB data cable to use with external power and other devices which can accept Garmin's USB data format (i.e. depth finder, water speed and temperature indicator, autopilot), a 110 volt power supply which powers the unit and charges the battery, and MapSource Trip & Waypoint Manager.  (A serial port for NMEA-0183 output is available and requires an optional cable, not included with the package. List Price for the optional cable is US$38.09)  Although listed as a marine unit, the GPSmap 276C is quite suitable for using in an automobile when programmed with the MapSource CityNavigator highway maps.  With three swivel joints on the mounting bracket, the unit can be fixed to about any angled surface and still be adjusted for easy viewing.  Also available is an automotive mounting bracket for using it in a car.

The basemap, which is permanently installed, is Americas AutoRoute 1.00.  It shows the countries and major cities around the world, and major highways in North, Central, and South America.  It contains information about businesses, service stations, restaurants, lodging, marinas, and many other points of interest.  If you load another map in the data card memory that doesn't support auto routing, the GPSmap 276C will still create a route following the roads of the basemap.  Since this map doesn't have all the detail of some of the other maps, you may see some parts of the route that don't follow the roads of your data card maps.

A cable included with the unit can be connected to a DC source of  11 to 35 volts DC for external power.  If it loses external power, it will sound an alarm and display a message that it will shut down in 30 seconds.  Pressing any key will switch it to internal battery power.  If the external power is restored before the 30 second timeout, it will resume operating on the external power.

The antenna is attached to the back of the unit and can be rotated down out of the way when not in use.  It can be removed and an external antenna can be attached if it is desirable to have the unit located in such a place that it cannot receive data signals from the GPS satellites.  While the unit's antenna is reasonably robust, care should be used in removing it to avoid damage. See the details on this later in this review.

This particular unit has internal system software version 2.60, the latest available at the time of writing.  Any future updates can be obtained from the Garmin web site at no charge and loaded into the device.

There is no internal memory for maps other than the base map, which can't be changed.  Other maps are loaded into a removable data card.  It uses either pre-programmed maps such as BlueChart, or Garmin blank data cards into which MapSource maps can be loaded by use of an external IBM compatible PC.  These cards are available in 8 Mb to 256 MB (Street prices for the 256meg memory card are now under $150.  Check prices HERE.)  and must be purchased from Garmin or one of their dealers.   The list of maps and the information about them is too vast to be included as part of this review, but descriptions and details of these various data cards, CD's and the MapSource programs can be found under cartography on the Garmin Web site HERE.

If you don't already have a Garmin MapSource program, the MapSource Trip & Waypoint Manager that comes with the unit allows the user to set up waypoints and routes on a PC and download them into the unit.  The disc also contains the drivers needed for programming the unit via the USB port.  There are no downloadable maps in this program, but you can get started right away without the need for a data card since waypoints and routes go into the unit's internal memory and do not require the optional memory card.  (Note that NO memory card is furnished with the equipment.)  You can enhance the details with a mapping program such as CityNavigator for automatic car navigation or Fishing HotSpots for Marine use as the need arises.  Although the GPSmap 276C supports the automatic routing feature which follows the roads, the Waypoint & Trip Manager creates straight-line routes from waypoint to waypoint.  Once loaded into the unit, you have the option of having it follow the roads on the basemap.  For downloadable maps which contain much, much more detail and information, you must buy a MapSource mapping program and a data card.  Garmin recommends MapSource CitySelect for the GPSmap 276C but CityNavigator will also work.  If you already own CN or CS for use with another Garmin unit,  you can use either of these programs in TWO Garmin GPS units without purchase of another license.  These mapping programs provide  automatic routing and will generate automatic car navigation routes within the GPS.  Of course, in the marine mode it will show straight line courses between waypoints.  For marine maps the BlueChart navigation charts work well in this unit.  For combination automotive, marine, and hiking or off road exploring, the US Recreational Lakes With Fishing Hot Spots is excellent.  These maps not only show the details of selected fishing lakes, but show the small streams, trails, back roads, and recreational areas, as well as highways.

The GPSmap 276C will store 3000 waypoints, 50 reversible routes of 300 waypoints each, and 15 tracks.  Routes can be inverted for following it back after you get to your destination.  Note: Reversing routes in car navigation mode is not advisable as one way streets and expressways can generate strange results.  In general,  for best results with car navigation,  you should let the built in automatic route generation do the work.

The Acquisition times posted in the manual are: warm start, 15 seconds, cold start, 45 seconds, auto-locate, 5 minutes.  The evaluation unit bettered those specifications.  However, the unit had a location in Taiwan when received and initially obtaining data from the satellites took nearly 8 minutes.  This was probably due to the heavy tree cover.  Position accuracy specification is 15 meters (49 ft.) at 95% confidence and 3 meters (10 ft., 95% confidence) with  WAAS turned on.  Both specifications are for operation with a CLEAR SKY VIEW.   With a clear view of the sky and WAAS enabled the unit estimated an accuracy as low as  6 ft. (less than 2 meters).  (Note: This "estimated accuracy" is just an estimate and should not be relied upon.)  When the unit first starts searching for WAAS, it searches for all the WAAS satellites, even though there are only two at this time.  It may take several minutes or longer to finally locate the one available (shown on the screen as number 35 in most of the US) and get it's location.  This Eastern USA positioning satellite is geostationary (remains in a constant location with respect to earth) and is about over the east coast of Brazil above the equator.  If you can get a clear, unobstructed view in that direction it will locate it much quicker.  After that, it will more  quickly locate  it.  See sample of position measurements made with a similar receiver at a fixed location and out in the clear away from trees, etc. HERE.  Note that WAAS may not be satisfactory everywhere and there is nothing that can be done until the FAA gets more  than the current two WAAS satellites available.  The unit should also operate with the European WAAS equivalents but this was not tested.

The list price of the GPSmap 276C is US$747.00.  Click (HERE) for latest prices.


All the control keys are located on the front, just to the right of the display.  The control keys include OUT, IN (zoom), PAGE, QUIT, ENTER/MARK, MENU, NAV/MOB, FIND, POWER (Also used for backlight level, speaker volume, battery condition, and battery time left), and the ARROW Keypad.  They are lighted for easy viewing in the dark.  These keys and their function will be described below.

When the Power key is pressed or external power is supplied, the unit comes on with a picture and backlighting set to the same level as when it was turned off.  By pressing the ENTER key it will continue through the Welcome screen (you have the option of inserting text such as your name and phone number on this page), again press ENTER to a disclaimer screen, and again press ENTER to the Main Menu.  If the ENTER button is not pressed, it will time out in about 30 seconds and go through the screens anyway. The GPS status screen will appear at this point and the unit will be searching for GPS satellites.

When data is received from three satellites it goes into 2-D location and will switch to the MAP page.  Data from a fourth satellite will put it in 3-D location mode, which will include altitude.  Your location on the map will be indicated by an arrow in the center, pointing in the direction of travel.  As you move, the map will scroll keeping your location in the center so you can see where you are at that instant relative to surrounding roads, cities, or even states.  Pressing the IN or OUT KEYS will zoom in or out to change the map scale which is indicated in the lower right corner of the screen.

The backlighting can be adjusted by pressing the Power key from any page or screen location.  Since holding this key in for more than a second will turn the unit off, quickly press and release the key.  The first press will bring up the Backlight window.  Further presses of the Power key will cycle the backlight through last mid-range setting, full, off, and then repeats.  With the window displayed, the ARROW key up or down will control the backlight setting, and left or right will control the speaker volume, if you have that accessory.  Pressing QUIT will close the window, or it will close itself in about 30 seconds.  This window also shows if the unit is on internal or external power, battery level, and time of use remaining at the current backlight level.

Navigation is the term used when the receiver is programmed with a route to direct you to a certain location either in a single straight line, a series of straight lines connecting waypoints, or by following a route along roads and highways.  The GPSmap has two modes for navigation: Automotive and Marine.  Either can be selected by holding down the PAGE key until the menu shows.  The map colors and details are different, navigation pages are different, and you can set the parameters for each without changing the other.  For instance, in the automotive mode you can select statute miles for distances, and in marine select nautical miles.  When you switch back and forth the numbers change as well as the page setup you selected.   There are seven pages used for navigation, but two are for automotive only and two are for marine only:  They are: MAP page, COMPASS page, HIGHWAY page, ACTIVE ROUTE (marine) or CURRENT ROUTE (automotive) page, and POSITION DATA (marine) or TRIP COMPUTER (automotive)  page.  The page sets are automatically selected when you switch from Automotive Mode to Marine.  By default the COMPASS and HIGHWAY pages are not shown in the automotive format, but can be turned on if desired.  Likewise, they can be turned off in the Marine Mode.  Also by default, only the MAP and TRIP COMPUTER pages are shown when not navigating a route since these are the only two you need.  The available pages are brought up in sequence by pressing the PAGE key, and will go in reverse sequence by pressing the QUIT key.  The description of these navigation pages will assume that we are navigating a route that has been entered into the units memory.


The MAP page displays the map you are using, either the base map or a map from a data card that has been programmed into the unit.  A map from a data card will override the basemap unless that map is turned off from the main menu.  The waypoints will be shown and the route will be indicated by a magenta ribbon.  The appearance of these features can be modified or turned off if desired.  By default, there are five data fields on the right of the screen showing speed, distance to next waypoint, estimated time enroute to the next turn, estimated time of arrival at destination, and a pointer showing which way to turn to follow the route.  This display can be customized to your own tastes or needs.  You can choose a full screen map with no data fields, or change the number, size and position of the data fields.  You can also change what's in the data field to many items including odometer, average speed, maximum speed, time of day, and others.  You can measure the distance between any two points on the map, and change the map setup.  The setup includes many things such as orientation of the map either North up, track up, or course up; turn the various installed maps on or off; change the size of text for the various items on the map; turn on or off the accuracy circle around your position; plus other details on the map display.  On the MAP page you can use the map panning feature by pressing the ARROW key in any direction.  A pointer appears on the map that you can move to any location in the world.  Press the OUT key to increase the scale of the map so you can move quickly to a distant location, then press IN to zoom in for more detail.  This will allow you to see details of other locations, find services at Interstate exits, see facilities at points of interest, or create waypoints.  See Additional Features later in this review for more information.



   Automotive Mode (City Select)                          Marine Mode (Fishing Hot Spots)
(Note that route follows the roads)                         (Note that route is straight lines)

The COMPASS page displays a compass which rotates to show your heading or track at the top, and an arrow on the compass to show the bearing to the next point in navigation, the name of which is shown at the top of the screen.  There are five data fields which can be deleted or modified in the same manner as those on the MAP page.  If the arrow is straight up, you know you are heading straight for the next point.


                        Compass Page (Automotive)                            Highway Page (Automotive)

The HIGHWAY page displays what looks like a highway leading to your next points which are shown as a road signs in the distance.  You can turn these on or of, or only show the next, as shown above.  As you head for the next point you can see graphically how well you are on course, as well as viewing the five data fields.  Again, these data fields can be modified just as in the MAP page.  There is a compass ribbon that shows the heading or track in the center and also shows a vertical bar indicating the bearing to the next point. Keeping these lines together indicates a heading directly towards the next point.  The scale of the highway can be changed to suite your needs by pressing the IN or OUT key.  The highway display can be set up to show or not show the active route, active leg, saved tracks or track log, as well as other waypoints that are not included in the active route.

The CURRENT ROUTE page displays a list of the turns on your route, which way you will turn, the distance to each one from your present position, the street name, the estimated time to the turn, and the estimated time of arrival.  By highlighting a turn and pressing ENTER you  can see the detail of the turn on a map.

The TRIP COMPUTER page displays your direction, time of day, speed, odometer, trip odometer, moving average speed, total average speed, max speed, moving time, stopped time, and total time.


The MAP page in Marine mode is similar to Automotive, with different colors and data fields on the page.  Of course, these can be changed. (see examples above).

The COMPASS page and HIGHWAY page are also very similar, with data fields suited more for boating.

The ACTIVE ROUTE page displays a list of the waypoints on your route, the course between each point, and the distance to each one from your present position.  A fourth column is selectable using the ARROW key.  Pressing the MENU key gives you an option of Plan Route, which then lets you select your desired speed, fuel flow, and depart time and date.  The fourth column on the page will then show the distance of each leg of the route, the fuel used for each leg, the time of each leg, the sunrise and sunset at each point, the time to each point, ETA at each point, and the total fuel used.  This page can be used to show each waypoint on the map, move, insert or delete waypoints, and rename the route or waypoints.

The POSITION DATA page contains a lot of data with respect to your navigation.  It can best be shown with the screen example below.  As with other screens, the data fields can be changed.



 When the GPSmap 276C is turned on and the warning screen is acknowledged (by pressing ENTER), it switches to the main menu with the GPS screen displayed.  This is not one of the main navigation pages and when the unit determines a 2-D location it switches to the MAP page and the GPS page is no longer shown in the page sequence.  Pressing enter will keep the unit at the Main Menu with the GPS screen displayed if desired.  Pressing the MENU key twice will bring up this Main Menu from any screen.  The tabs at the left of the screen let you select different sub screens.  The tabs are GPS, Route, Points, Track, Alarms, Celestial, Message, Display, Sound, and Setup.

The GPS tab, after acquiring data, shows a sky view with the number and location of the satellites with respect to the current location.  If WAAS is enabled it will show the location of the WAAS satellite(s).  At present there are two geo-stationary satellites (Inmarsat IIIs: POR (Pacific Ocean Region) and AOR-W (Atlantic Ocean Region-West).  More WAAS Information HERE.  The default  satellite view is shown with North at the top of the screen, but can be changed to show the direction of travel at the top.  It shows a bar chart of the satellite status: A white bar indicates it has located the satellite and is gathering data, a solid green bar indicates it now has the data and is being used in the calculations, and the letter D on the bar indicates that the satellite information is being corrected, either by a DGPS receiver or from a WAAS satellite.  This screen also gives the date and time, the battery condition, the accuracy of the location, and the differential status, if any is being used.  By noting where the satellites are from your location, you can tell if there is a clear view in that direction, or if you should move to get better reception.  There is a small red dot located on the outer ring of the sky view (the horizon) which indicates the current direction of travel.  If the view has been changed from North up to track up the dot is not present since the direction of travel is straight up.  From the GPS menu, you can start and stop the simulator, turn WAAS on or off, and set the unit to a new location or altitude.  The unit did not have a clear view of the WAAS satellite in the picture below.  Number 35 is the WAAS satellite available from this location.


  GPS Status Tab                                                Route Tab

The Route tab displays a list of the routes stored in the unit.  Some of the routes are marked with a small auto icon (see above).  The manual does not mention this, but these are routes that were generated in MapSource MetroGuide with autorouting.  At this tab you can review a route and the waypoints or turns, delete it, copy it, or make a new route.  You can activate it to start navigating or just show the route on the map.  You may have to activate it to see the turns and waypoints.  Reviewing a route shows a list of the times and fuel data as mentioned on that page.  A route can be created by using the pointer on the map to select points in sequence, or by selecting waypoints from the waypoint list.  You can start navigating a route from this page by highlighting the route and pressing the NAV/MOB key.  This brings up a menu that will allow you to navigate the route, make a new route, make a detour (if you know there are delays ahead due to construction), add or edit vias (places not on the route that you want to visit enroute).  You can Invert the route if you want to follow it back after you get to your destination.

The Points tab shows two other tabs, user and proximity.  The User tab shows a list of all the waypoints in numerical/alphabetical order.  You can use the down arrow to go through these one by one, or the right arrow to advance a page at a time to get to the desired waypoint more quickly.  You can add waypoints, delete them, or edit them from this list.  The proximity tab allows you to set a radius around a waypoint to sound an alarm when you get within that distance.  This would be useful for warning of a shallow spot or some dangerous area.

The Track tab allows you to manage the track, which is the path you have actually taken during your trip, regardless of waypoints or routes.  This is a "breadcrumb trail" that normally can be seen on the map.  If the record mode is on, this Active Track will be saved in memory.  You can then save it permanently to use in the TracBack feature which allows you to follow it back or to use it again later.  You can save up to 15 tracks.  The record mode can be set to Off, Wrap (continues recording when memory is full and deletes the beginning of the track), or Fill (records to fill the memory and quits recording).  This Active Track can be cleared from memory which is what would be done before recording a track you're interested in saving.  Otherwise the track would cover a lot more distance than you want.

The Alarm tab controls the settings for the various alarms.  For navigation these are: Next Turn and Arrival, which you can set for either time or distance, Off Course and Anchor Drag which you set for distance.  For the System, you can set a Clock alarm for a particular time of day, External voltage loss, DGPS loss, and Accuracy below a certain value.  The alarms can be turned on or off.

The Celestial tab has three other tabs for Tide, Sun & Moon, and Hunt & Fish.  The Tide tab will list the tide stations nearest your present location and show a graphical display of the tides as well as give the time and level of high and low tides.  You can change the date and location to see other tide data.  The Sun & Moon tab has data fields for Sunrise, Sunset, Moonrise, and Moonset.  There is a graphical representation of the current phase of the moon, and a sky view to show the location of the sun and moon.  The date, time, and location can be changed to show information for those parameters.  The location can also be selected from the map.  The Hunt & Fish tab predicts the best times of the day for hunting and fishing.  Again, the date and location can be changed.  (We make no comment on the accuracy of the best times to hunt & fish predictions.)

The Message tab has a log of the messages that you would see on the screen during use, such as Batteries Low, Transfer Complete, Approaching Turn, etc.  You can filter these messages so that only certain ones are kept in the log, and all others are ignored.  They will still show up on the screen, however.

At the Display tab you can change the display color mode to Night (with darker colors), Day (with normal colors), and Auto, which will automatically switch at sunset and sunrise.  You can set the Main Menu to show icons (see screen shot of GPS Page above), or just text, set the backlight to stay on or time out and turn off, set the level of backlight, and turn on or off the Highway and Compass pages in the navigation page sequence.

At the Sound tab you can set the beeper on or off, or for alarms only.  The GPSmap 276C has an optional 12 volt power cord with a speaker that will give voice guidance: tell you which way to turn, warn you of upcoming points, etc.  At this tab you can set the language, including American English or British English, and set the speaker volume.

The Setup tab brings up another set of tabs for setting the system parameters.  The System tab lets you select the System Mode: Normal, Simulator, or Battery Saver.  The simulator turns off the GPS receiver and the GPS screen appears to be receiving signals.  It cannot be used for navigation in this mode, but uses less power and is convenient for using indoors to set up maps, waypoints, and routes.  The battery saver mode turns off WAAS to use less power.  You can switch the usage mode from Automotive to Marine, but you can also change it at any time by holding down the PAGE key.  There is a Speed Filter that averages the speed over a period of time to filter out extremes.  This can manually set, turned off, or Auto.  The text language can be set on this tab in any of 15 languages.  The Road Routing tab lets you select the route preferences, calculation method, type of vehicle from bicycle to emergency, or even pedestrian.  You can set it to avoid U-turns, highways, toll roads, or unpaved roads.  On the Guidance tab you can set the way it notifies you of re-calculating a route if you get off course or miss a turn.  By default the unit will zoom in when you get close to a turn to show road detail in that area.  You can turn this off, or set it to show only when you press the NAV key.  The Timer tab has a timer set by the user to count up, down, or off.  This tab also tells the amount of time the unit has been turned on since midnight.  The Time tab is where you set the time format (12 or 24 Hr.), set the time zone, and automatically change time for daylight savings time.  The Units tab is where you set the measurement units for English, Metric, or Nautical.  You can have one type of measurement indicated when navigating in Automotive Mode and a different type for Marine.  The Location tab sets the format for latitude and longitude, the map datum, and direction reference for heading information.  If you select auto magnetic, it will show the magnetic variation for that location.  At the Welcome tab, you can enter a text message that comes up on the screen at startup.  This is a good place to put your name, address, and phone number in case the unit is found by an honest person.  The COM 1 and COM 2 tabs let you set up the input and output format for external devices, such as a depth finder or autopilot.


Garmin's proprietary data cards  (up to 256megs currently) are inserted into the GPSmap 276C to provide storage for detailed map data.  These can be BlueChart or other cards which are pre-programmed with map data, or blank data cards for programming from the MapSource maps.  Using the MapSource programs and associated map data on CD-Rom with a computer  makes it possible to select maps and download them into the data card using the PC data cable supplied with the unit.  This uses the USB port for loading maps as well as the waypoint and route data.  An optional serial cable is available if necessary.

The screens shown below are from MapSource US Recreational Lakes with Fishing Hot Spots, East, V5.  This shows the bottom contours and fishing information for many lakes east of the Mississippi.  Other programs cover the Central US and Western US.  If you get these maps on CD ROM the maps show not only major highways and roads, but most of the back roads, trails, small streams, recreational areas, and on and on.  It is a great map for the hiker and automobile traveler as well as the fisherman and boater.


US Recreational Lakes with Fishing Hot Spots, East, V5


If you want to locate the antenna remotely from the device for better reception, the antenna can be removed by turning it 45 degrees down from horizontal and GENTLY pulling it out.  There is a small tab on the antenna that you can see through a slot on the GPS base.  It is located 45 degrees clockwise from the top of the unit when looking at the back.  The tab must be aligned with the slot for the antenna to come out.  This antenna can be connected with a cable which can be obtained from a local electronics store.  Other external antennas can also be used to connect to the unit.

The ENTER/MARK key can be used to quickly mark your present location as a waypoint by holding it until the waypoint screen comes up..  It will automatically be given a 4 digit number as a name (or the name of the place  at your location) and can be edited later.  By panning the map with the ARROW key, you can make a waypoint at any location.  Pressing the ENTER button quickly will mark the spot as a waypoint.  Pressing the ENTER key for a second or two will mark your present location as a waypoint, not the location of the panning arrow.

The NAV/MOB (Man OverBoard) is used in a similar fashion.  When in the Marine Mode, pressing the key for a second marks the current location as a waypoint called MOB and brings up a screen that asks "Do you want to store and begin navigation to the MOB waypoint?"  "Yes" is highlighted, so simply pressing the ENTER key will start navigation back to that point.  If there is already an MOB waypoint it's coordinates are changed to the current location.

The FIND key is used to find waypoints, cities, map features such as interstate exits and rest areas, hotels/motels, restaurants, and on and on.  It will usually give addresses and phone numbers of businesses.  You can select them by name or by nearest, and the map panning feature can be used to find the items nearest another location.  Most of these are contained in the map set loaded into the unit, so the type and detail of the search items depends upon the map program.  This is very handy when traveling and you want to find the nearest McDonald's for the kids, or a Hampton Inn for the night.  You can select from many categories, and then sub categories to narrow down the search.

The GPSmap 276C can be put into a Simulation mode to see how the pages appear under actual navigation.  By selecting a route and activating it it the unit will appear as though you were actually traveling .  As you sequence through the navigation pages you can see the movement on the map and the updates to the Active Route page.


I found the GPSmap 276C quite easy to use and it's many features very helpful.  The map redrawing process is very fast.  This is important when zooming in or out or when using the map with track up.  The compact size makes it ideal for use in a car and I will use it for automobile travel probably more than boat navigation.  The ability to find rest areas, restaurants, and gas stations way ahead is a handy thing to have.  By attaching a cigarette lighter plug to the power cord you won't have to worry about battery drain and can leave the backlight on for better visibility or night use.  All in all I was very satisfied with the operation of the GPSmap 276C.

Things I would change are:

1. When changing from Automotive Mode to Marine, the map switches to a marine map.  If you don't have one, the map disappears and you're on the basemap, which is not accurate.  When navigating a river, you will be over dry land half the time.  Although you can turn the map back on, it will go off the next time you switch back and forth.  I would like to set the the maps on or of for Automotive or Marine, and have them stay as I switch back and forth.  Fortunately, I have MapSource Roads & Recreation which it must consider a marine and automotive map as it stays on in Marine Mode, but comes back on when switching to automotive, even if I turned it off.

2. When going back to Automotive Mode, the Lock to Road turns back on.  I like to leave this off, and have to go in and manually turn it off.  The map is not very accurate around my home, and my indicated location hops around from road to road.

3. The only battery that will fit into the unit is the re-chargeable Lithium battery.  If the battery dies while you're out traveling and you don't have the optional cigarette lighter cord and 12vdc, you can't just go to the local drug store and buy new ones.  You are out of luck until you get somewhere that has a 110 VAC outlet.  You could buy an extra battery, but the list price is US$60.  An option would be a snap in pack that holds 8 AAA batteries.

4. If you want to follow a route backwards in marine applications, you must select the route, then invert it.  I would like to see the option of "Activate" or "Reverse and Activate" for ease of following a route back after you get where you're going. 

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