Garmin GMR 18 HD 4KW Radar

Garmin GMR 18 HD 4KW Radar review. Details of this review are courtesy of Tom Schubert who let us look at his yacht a Grand Soleil 47ft. Tom spends lots of time cruising around the east Coast and Caribbean and races as navigator on long distance races. Tom notes that with the present setup of the GMR18 and the Garmin 3210 chartplotter he does not use his PC and Nobeltec software anymore.

Tom told us the gamins HD radar is the best he has used and he is an ex Merchant marine navigator, so he should know. He also likes the intuitive soft keys and moving around the Garmin 3210 display and is glad he added the radar package to his marine electronics system. Discussing the detail of radar images he notes that an open array would yield better clarity but at higher cost and size.

The Garmin HD radar is shown here on a scanstrut radar mount with additional antennas

Garmin’s Description.

Sharpen your radar picture with high definition performance. The GMR 18 HD marine radar offers a whole new level of radar scanning capability. Get Powerful Performance The GMR 18 HD features high-powered Digital Signal Processing, providing sharper radar imagery and improved target separation. This 18-inch, 4-kilowatt high definition radar has a 36 nm range, bringing radar images into even clearer focus. Combine that with the antennas 5.0 degree beam width, and you are looking at the best weather penetration and target definition in its class.

To help you avoid traffic on the water, the GMR 18 HD provides MARPA target tracking when combined with a multi-function display and an optional heading sensor. MARPA tracking allows you to track the bearing, course, speed and predicted closest approach of up to 10 targets. In addition, like all Garmin radars, the GMR 18 HD has self-contained signal processing, which provides you with a more precise, easy to read signature. Connect to the Garmin Marine Network The GMR 18 HD transmits data over the Garmin Marine Network, a 100-megabit plug-and-play proprietary network that gives you the ability to expand your boats system as needed. Once connected to the network, you can use any network-compatible Garmin chartplotter as your radar screen. And as an aid to location awareness, you can overlay the GMR 18 HD digital radar image on the chart plotters map page. You can also split the on-screen display so that you can view the map and the standard radar page simultaneously.

Garmin have brought much of the processing within the radar dome, which allows for all the conveniences of radar with your Garmin Marine Networked Plotter and not too much installation hassles. External plug in cables for data and power make installation quick and easy.

Cost of a Garmin HD radar GPSMAP setup

The GMR 18 marine radar priced as low as $1,000 online while the GPSMAP 3210 costs around $1,400 – 1,500. You will need to get a radar mounting unit like the scanstrut and include installation time, but this is a very reasonable radar package.

You could use any of the Garmin GPS MAP displays and maybe the 5000 series touch screen is one option.

HD radar features & benefits

When looking at choosing a radar what are the features you should be looking at?

Beam width for a radar dome like the Garmin GMR18 is around 5 degrees. You can upgrade to the Garmin 24 HD and get 3.6 degrees but at almost double the cost. To get a smaller beam width you need to go to an open array. Open arrays are twice the size of a the GMR18 dome in terms of diameter and can cost 2 or 3 times more money. In this case the 18 inch dome is a good size for this 47ft yacht.

BEAMWIDTH, as the name suggests, is the width of the radar beam, and ranges from 7 degrees for the smallest sets down to less that a degree for a large ships set. You can appreciate its significance if you imagine yourself looking for a narrow harbour entrance. If the entrance is to show up as a gap, the radar beam has to pass straight through it with out being reflected from either side. If it is 0.1 wide, for instance, a 1 degree beam will pass straight through when you are 6 miles away, but if the beam width is 6 degrees, you will need to be within a mile before it will show up. The British Marine Electronics Association has provided this information on Radar and beamwidth.

HD (High definition) digital; radar images help define targets and as they are sharper and more clearly defined. Picking out targets be they land, buoys, boats markers.

Digital Signal Processing (DSP); is a feature available to digital radar signals and helps with details of the radar image. Digital radars can apply DSP to the return echoes, which preserves the signal strength for better signal to noise ratio (SNR). Check to see if the radar offers DSP as it will increase the clarity of the images.

Radar scanner Power; Radar works by line of sight. Marine radars range may be quoted as 36 miles but if your radar is 10 feet above the water and a target is just 15 ft off the water, your actual range will be closer to 9 miles. In most cases you are looking a objects much closer such as local traffic and land masses. One reason to look further will be weather.

In most cases, a 4KW system will provide plenty of range for you when you are out at sea. 4KW is a mid range device, and for a larger boat may want to invest in a 6KW system, particularly if you looking for a wider range of sight.

MARPA tracking; Because the targets are easily defined you can pick out potential hazards and acquire them as targets and track them with MARPA.


Connect radar to Chartplotter

After Installing the boats radar and connecting the radar to the chartplotter, you should detect the radar and the radar page is added to the menu.

In the case of the Garmin radar scanner installation was easy with only two plugs to contend with.

Now you can access the radar pages


Controlling the Garmin 18 Radar Features

To get to the radar adjust menu press ADJ/MENU form the soft keys on the right.

Garmin 18 Radar Features
Garmin 18 Radar Features

Once in the menu you can access settings for Gain, Sea Clutter, Rain Clutter, FTC, Zoom, Target Expansions, Trails, Guard Zone, VRM/EBL, MARPA and hide show navigation features.

Guard Zone can be set and any vessel entering the zone will set of an alarm.


Garmin GPSMAP 3210

The Garmin GPSMAP 3210 is a full featured Chartplotter that costs around upwards of $1,400 online.

Understanding the Display

Garmin GPSMAP 3210
Garmin GPSMAP 3210

Rings let you know how far targets are away from you, you are the center.

You can position the center in the center of the display or move to the bottom so you can see more ahead of you.




Mini Automatic Radar Plotting Aid (or MARPA) is a radar feature for target tracking and collision avoidance. Targets must be manually selected, but are then tracked automatically, including range, bearing, target speed, target direction (course), CPA (closest point of approach), and TCPA (time of closest point of approach), safe or dangerous indication, and proximity alarm. MARPA is a more basic form of ARPA (Automatic Radar Plotting Aid).

*Garmin suggests the KVH 1000 heading sensor for MARPA tracking

MARPA tracking is probably the biggest benefit of a radar system for your boat. The Garmin allows you to track up to 10 targets and if any of them get inside your pre set guard Zone an alarm will go off.

chart radar overlay

this chart radar overlay @ 1/4 nm range with Chart details hidden
this chart radar overlay @ 1/4 nm range with Chart details hidden

this chart radar overlay @ 1/4 nm range with Chart details hidden

The Gamin comes with US charts and Tom only had to by Caribbean and Bermuda Charts to complete his cruising requirements. He also notes how easy it is with Garmin to upgrade with a card reader he had to purchase and then download from the Internet.

The red bar across the top of the screen is showing a MARPA target inside of alarm range


VRM/EBL soft keys

VRM stands for Variable Range Marker. It is an electronic mark or ring that can be placed over any target on your radar display. An on-screen digital readout will let you know the precise range, in nautical miles, between the target and you

EBL is the Electronic Bearing Line.

Top line shows; One radar target acquired showing bearing and distance as well as course and speed. You can use this to calculate CPA. (Closest Point of Approach.)



Radar w MARAPA or AIS

Simrad HD Radar
Simrad HD Radar

Tracking all vessels in your local waters on your chartplotter is a benefit of radar and AIS.

So Which is best for navigation, Radar or AIS?

Radar Radar can show all vessels in your vicinity, it can also show weather and land masses.

These are the good features, however a Ship may not see you as passive radar reflectors (carried by small vessels) are not that efficient. If you do not show on a ships radar you better keep out of their way.

Other negatives to Radar are that its complicated to read and takes skill to use, Also weather and rain can clutter the screen. You can use rain clutter or FTC, but this may weaken representation of other targets.

AIS AIS is a message sent over VHF frequencies indicating course, speed, and position of commercial shipping. As a recreation boater you can receive this signal with an AIS receiver and have the target automatically show up on your chartplotter, you can also send your own signal.

AIS is a requirement for all vessels over 300 gross tons. However not all traffic will be sending AIS signals, so you won’t get a complete picture.

It is similar to MARPA in that you can see a target on your chartplotter, but with AIS you will get a message on the screen indicating the vessels name destination and call signs, so you can call them on the VHF radio.

AIS has the capability to see around a bend also. See diagram in the newsletter below. This also translates to bad weather. Squalls and rain storms can produce a lot of clutter on a radar screen, while the AIS plot will still be clear.

The negatives to AIS is that not all vessels are not required to transpond. Fishing vessels are one example and they may like to keep their location secret.

Bottom line both AIS and radar have their merits. They also have their downsides, so there is no one choice. You can use both and some systems allow you to overlay AIS and radar on your chartplotter.

This Video from Motor Boat & Yachting demonstrates this

Map and radar overlay

By using the chart radar overlay the less skilled radar reader gets to understand the blips and targets much easier.



This section provides further reading and information on how to install radar and how to use and read a Boats Radar display.

Garmin 3210 manual in PDF form can be found here which includes the radar operation

Marine RADAR
Marine RADAR

Marine RADAR

The USPS recommend this book This seminar covers how radar functions, radar selection, operation of the radar under various conditions including setting of controls, display interpretation, basic navigation, and collision avoidance using radar. The kit includes The Radar Book written by Kevin Monahan ($25 retail) and Student Notes with copies of slides.