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Garmin GPSMAP 840xs

ProductDisplay SizeSonarMax. Depth
GPSMAP 840xs

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2,700'10 Hz,
US LakeVü HD,
BlueChart g2,

In this post, we’re going to address the Garmin GPSMAP 840xs, the newer 2017 model, part number 010-01181-02. This unit is typically sold without a transducer, but the one we’re covering here does come with the classic GT20-TM. The unit has ClearVü and 2D CHIRP sonar, and comes pre-loaded with the LakeVü and BlueChart g2 HD charts, offering quite a consistent bundle of features and functions.

Technical Details and Specifications

  • Display: 8″ diagonal WVGA color multi-touch display, 800H x 600V pixel resolution, with LED backlight
  • Sonar: CHIRP 2D, CHIRP ClearVü
  • Frequencies:
    • 2D: 50/77/200 kHz
    • ClearVü: 260/455/800 kHz
  • Depth capability:
    • 2D: 1,900 ft (579 m)
    • ClearVü: 750 ft (288 m)
  • Transducer: GT20-TM (8-pin)
  • Power Draw: 12 VDC, 1.1 Amp
  • Power Output: 1 kW
  • GPS: 10Hz, Internal
  • Charts: LakeVü HD and BlueChart g2 HD
  • Routes, Waypoints, Tracks: 100; 5,000; 50,000 points (50 saved tracks).

Sonar and transducer

The Garmin GPSMAP 840xs offers an impressive array of sonar capabilities. To begin with, it has traditional 2D CHIRP sonar and ClearVü sonar, which are ready-available with the included GT20-TM transducer. However, the unit is SideVü capable with an external GCV™ 10 scanning sonar module (which is not included). Also, this unit is Panoptix sonar capable, if paired with a Panoptix Down transducer (also not included), making available LiveVü Down, RealVü 3-D Down and RealVü 3-D Historical sonar views.

The unit itself is capable of three main operating frequencies for 2D and three for ClearVü, these being 50/77/200 kHz, and respectively 260/455/800 kHz. With the included transducer it will only be able to use the 77/200 kHz modes, and 455/800 kHz, though. Differently put, this Garmin fish finder will make available Medium CHIRP and High CHIRP modes for 2D, and a CHIRP pulse modulation between CHIRP 435-475 kHz and CHIRP 800-840 kHz for ClearVü. CHIRP sonar is superior to single-frequency sonar as it modulates the pulse over an entire range of frequencies, which results in clearer images with less clutter, and targets contoured better with a clearer separation from one another.

The included GT20-TM transducer features 20′ (6 m) of cable; it has an 8-pin connector and an internal temperature sensor. The unit itself can display water temperature, having Temperature Log and Temperature Graph functions.

With the included GT20-TM transducer, this Garmin fish finder offers a depth capability of 1,900 ft (579 m) for the 2D CHIRP sonar and 750 ft (228 m) for ClearVü. However, with a 50 kHz capable transducer, such as Airmar B260, the unit can scan depths up to 2,700 ft (823 m). Also, the transducer should be able to maintain a decent bottom reading at speeds up to 35 MPH, but the recommended speed for the best quality imaging and a maximum of targets detected is trolling speed (up to 10 MPH).

This Garmin fish finder offers several standard sonar functions, among which we can count Fish Symbols, A-Scope, Bottom Lock, Temperature Graph, Sonar Recording, Sonar Rewind, Depth Alarm, Fish Alarm etc.

Sonar Recording and Sonar Rewind are functions that require the unit to have a blank microSD card inserted in one of its slots. As a general idea, 15 min. of recording will take approx. 200 MB on the card. The sonar recordings can also be played on a PC via the HomePort free application.

The Fish Symbols function replaces the fish arches or the suspended targets, with fish symbols. It’s usable only with the 2D sonar, and also displays the depth of each fish target next to it.

A-Scope is a vertical flasher view, which is typically attached to the 2D sonar view. It displays the information caught by the most recent sonar echo. It can be useful if you want to know exactly when the sonar beam hits a fish or a group of fish. Bottom Lock is a function that allows the sonar image to maintain a specified distance from the bottom, focusing directly on the bottom and the water in that selected depth range. It’s a function great to use if you’re looking for fish that are feeding on the bottom.

Navigation features

As opposed to other Garmin fish finders, such as the echoMAP CHIRP 74cv or echoMAP CHIRP 73cv, the GPSMAP 840xs includes two sets of cartography: LakeVü HD and BlueChart g2 HD.

The Bluecharts are best used for off-shore fishing as they cover the U.S. coastal waters and the Bahamas. These charts offer information and navigational aids including spot soundings, depth contours up to 1-foot, tides, currents, harbors, and marinas. They also offer the Multi-Depth Range Shading function which allows you to color code up to 10 depth ranges in order to view them at a glance.

BlueChart g2 Charts

The LakeVü charts cover more than 17,000 U.S. lakes, rivers, and reservoirs, out of which 13,000 are shown in HD, with 1-foot contours shoreline to shoreline. These charts offer excellent support for inland fishing. They have the Shallow Water Shading function, similar to the Multi-Depth Range Shading, function that allows you to designate a minimum depth. Interstates, highways, general roads and bridges, fishing areas and other points of interest, such as docks, boat ramps, marinas, and campgrounds are also included with the LakeVü charts.

LakeVü HD Charts

Evidently, the unit’s charts can be upgraded to LakeVü HD Ultra and BlueChart g2 Vision. These are premium charts that offer much more detail and information. For example, the BlueChart g2 Vision offer two types of 3D chart views including Marinerseye View and Fisheye View. They also include high-resolution satellite imagery. Conversely, the LakeVü HD Ultra offer 3D lake imagery, dynamic lake levels and custom depth shading. Both Ultra and Vision charts have the Auto Guidance function, which calculates a suggested safe route or path to follow,

Needless to say, the unit is equipped with an internal high-sensitivity 10 Hz GPS/GLONASS receiver, which refreshes your position 10 times per second, showing the boat movement in real-time without jumps from one point to another. The unit also uses the GPS data to calculate the speed of your boat.

The QuickDraw Contours function is also available with this unit. This function uses the sonar depth measurements to add depth contours to your maps. In other words, if a certain body of water isn’t covered in detail by the charts of your unit, you can re-chart that particular body of water, and get the most up-to-date contours.

In terms of navigation, this Garmin unit can support various external modules such as AIS and RADAR unit, and also allows you to see data from various NMEA 2000 sensors, such as engine data, wind data or live XM weather data.

Last but not least, the unit offers several special sailing features. The supported sailing features include laylines, enhanced wind rose, heading and course-over-ground lines, true wind data fields, and tide/current/time slider. Gauge displays are designed to provide important information at a glance, including true and apparent wind angle, true or apparent wind speed, set and drift, horizontal or vertical graphs, and a data bar with customizable data fields.

Control unit features and functions

The Garmin GPSMAP 840xs features an 8-inch display, SVGA color, with a pixel resolution of 800 x 600 and integrated LED backlight. The backlighting properties make the display readable even in direct sunlight and from sharp angles. As opposed to the GPSMAP 741xs unit that we’ve previously reviewed, this one has keypad navigation; it’s not touchscreen.

In terms of connectivity, the unit offers NMEA 2000 support. It has two inputs and two outputs for NMEA 0183, and an SD card reader (not microSD) with two card slots, for chart upgrades, blank cards for data backup etc.

It also has wireless connectivity. Garmin Helm allows you to view and control your unit from an OS or Android tablet or smartphone. You can record the streaming on your tablet and use the recording to show your friends, or re-examine later, etc. Also, the BlueChart Mobile free app gives you the possibility to plan marine routes on your OS or Android device and transfer them to your Garmin unit.

The unit supports DSC (displays position data from DSC-capable VHF radio). It’s compatible with Garmin Meteor Audio Systems and FUSION-Link radios. It also supports AIS units.

Last but not least, the unit comes with two mounts, bail and flush, and a protective cover.

The Pros

  • CHIRP technology offering superior clarity, target separation and target definition, for both HD-ID and ClearVü;
  • Transducer included;
  • Supports SideVü sonar, via the GCV™ Black Box external module;
  • Supports Panoptix sonar if paired with a Panoptix Down transducer;
  • Dual-frequency sonar;
  • Compatible with a wide selection of transducers from Garmin and Airmar, including 1 kW models;
  • Sonar recording and rewind;
  • Fast and accurate 10 Hz internal GPS;
  • Preloaded with the U.S. LakeVü HD and BlueChart g2 coastal charts;
  • Quickdraw Contours function, for the possibility to add contours and customize your maps;
  • Multiple Depth Range Shading;
  • Compatible with the Garmin premium charts, such as BlueChart g2 Vision or LakeVü HD Ultra;
  • Tide tables information;
  • Data graphs and information from other NMEA 2000 sensors;
  • Supports AIS and DSC-capable VHF radio;
  • Garmin Meteor™ Audio System compatible;
  • Supports FUSION-Link™ compatible radios;
  • NMEA 0183 connectors and NMEA 2000 support;
  • Dual SD card reader;
  • Wireless connectivity;
  • Bail and flush mounts included;
  • Unit cover included;
  • Easy to install;
  • Straightforward, comprehensive operation.

The Cons

  • Manual may not apply directly to this unit but to all the 500 and 700 GPSMAP units.


The Garmin GPSMAP 840xs is a fish finder and chartplotter unit equipped with CHIRP 2D sonar, ClearVü sonar, and an extra fast 10 Hz internal GPS. It includes the GT20-TM transducer. It comes preloaded with the BlueChart g2 coastal charts and the LakeVü charts for the U.S., and also has the QuickDraw Contours function. It offers an impressive array of connectivity possibilities, including wireless connectivity. These being said, it’s an excellent unit for freshwater and saltwater fishing, and for fishing boats of all sizes, except maybe small kayaks and inflatable boats.

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