Small-Screen Plotter/Sounders: Lowrance Bests Garmin and SI-TEX

High-resolution and fine sounder detail give Lowrance the win.

Small-Screen Plotter/Sounders: Lowrance Bests Garmin and SI-TEX

Four years ago, we concluded that it made little sense to buy an ordinary depth sounder when, for the same price or slightly less, you could buy a decent fishfinder that shows the bottom contours, wrecks, fish, and more. This becomes all the more obvious as you stray off the beaten path. Anyone who’s tried to keep their anchors free of the wrecks that litter the bottom of foreign ports with long histories (Penang, Malaysia, comes to mind) or the reefs of the deepwater anchorages (The Society Islands in French Polynesia qualify here), will vouch for the advantages of a graphic representation of the bottom. And with today’s color sounders, experienced users have been able to tweak the gain settings so that they can distinguish between soft and hard bottom by the color of the return.

Now the argument for fishfinders takes a new twist. Why buy just a plotter, when for less than the cost of a dedicated depth sounder you can add fishfinding capabilities to the plotter? Aside from avid divers and fishermen, these combo plotter/sounders will appeal to two types of sailors who’ve no inclination to catch supper or play Jacques Cousteau:

Sailors of small boats (particularly tiller-steered boats, or others with no binnacle pods) who have neither plotter or sounder and would like both without spending a fortune. Though they can be flush-mounted, these compact units will fit nicely on a swing-out bracket at the companionway, where you can check your position from the cockpit or belowdecks. Key data boxes (speed over ground, course over ground, depth, bearing to waypoint) are viewable from more than five feet, so you can still monitor this from the helm of most small boats, even when the unit is mounted at the companionway.

Cruisers on tight budgets who want a compact plotter/sounder combo for their binnacle pod, enclosed helm, or below a hard dodger. For bigger spenders, the cheaper units could also serve as inexpensive back-ups for black box plotters and sounders.

Two caveats to consider before opting for a combined plotter/sounder approach. The main argument against integrating the plotter and sounder functions—this also pertains to other key electronics—is that if the unit fails, you’ve lost at least two essential functions. But it’s getting harder and harder to find dedicated single-function electronics these days, and most boats still have a working sounder that can serve as a backup. Which leads us to the second caveat: Operating two sounders on the same frequency can cause neither to function properly. The units we tested can be switched between 200 kHz (the standard for most stand-alone sailboat sounders, good for shallow-water definition) and 50 kHz (better for deepwater probing). You could operate these units on the 50 kHz frequency while your stand-alone pinged at 200 kHz, but the 50 kHz may become ineffective in less than 12 feet of water.

What We Tested
We limited this plotter/sounder combo test to units with color displays 6 inches or smaller (measured diagonally). Next month, we review color combos with screens from 6 to 7 inches.

Garmin supplied two units, the 178C and the 198C. We used a BlueChart map card of South Florida in these machines. Lowrance sent us its LMS-337C DF and the NauticPath Coastal electronic chart. SI-TEX loaned us a ColorMax 6 and black box sounder, the ES502. We used a C-MAP NT card covering South Florida in the ColorMax 6. All display units tested are waterproof.

How We Tested
The Garmin 198C, Lowrance LMS-337C DF, and the SI-TEX ColorMax 6 were mounted on a portable base for side-by-side review. The trio was temporarily affixed to our 16-foot test power boat just above the fourth unit, the Garmin 178C, which is permanently installed for long-term testing. We rated the viewability of each unit under a variety of light conditions, from bright sunshine to nighttime darkness. In the daylight, the tester looked at the screen from various angles, with and without polarized sunglasses, and from differing sun angles. During night testing, we paid particular attention to the quality and adjustability of the unit’s backlighting. The tester viewed the displays from a distance of 2 to 3 feet.

Sounders were evaluated over known bottom structure in depths from 2 to 35 feet. We used the transom-mount transducers that were shipped with each unit. All sounder testing was done in 70-degree salt water. Sounders were judged on their ability to show bottom detail, their ease of use, and features.

We rated each chartplotter for user interface based on the unit’s buttons, cursor pad or joystick, and—most importantly—its software. The easier and more intuitive a unit was to operate, the higher we rated it. We used each unit’s supplied GPS antenna to receive satellite position signals. Three units used external antennas; all were mounted in close proximity to minimize variations in position data. We placed them in an unobstructed location just behind the display units to provide the best satellite signal reception. As we cruised, we used each unit’s course predictor, entered waypoints, edited them, deleted them, and checked the man-overboard function. We also set up a 15-waypoint route from a nearby creek mouth to the Gulf of Mexico to access route building.

Power usage was measured with a Sperry multimeter, with the sounder pinging away and the screen set at maximum daylight brightness.

Installation of any of these units requires mounting the display head, the transducer, and, if so equipped, the external antenna, plus running the necessary wiring.

Garmin 178C
Our Garmin 178C, the smallest unit tested, was equipped with an internal GPS antenna, an integral sounder, and a dual-frequency transducer. Other models of the 178C are available with an external GPS antenna and single-frequency transducer.

All wiring for power, interface, and transducer leads hooks to the back of the unit with a single multi-pin twist-lock connector. The transducer branch connects to the transducer with a twist-lock connector. For us, wiring the 178C was simply a matter of connecting the power wires to the source. If you were planning to interface the 178C to another electronic instrument, like an autopilot, you’d have to make several connections with some very small wires. Overall, installation of the 178C is the easiest of the bunch.

Thirteen levels are available for screen brightness and contrast adjustment. The brightness control range is adequate and the contrast control is effective. Two color palettes, sun or dark, can be selected from the map tab on the main menu.

In daylight, the 178C was easy to see, though we did note some tendency to reflect. It showed almost no screen darkening when the tester wore polarized sunglasses. The screen does have an occasional problem with overheating when it is exposed to long periods of direct sunlight. Once the overheating starts, the screen begins to lighten and eventually goes blank. The screen will come back on if you shade it for a few minutes to help it cool down. We rated the screen Good for daytime and nighttime viewing. Pushbuttons and the cursor pad are backlit.

Most functions on the 178C are manipulated through multi-layered menus. Hitting the Menu key twice brings up the main menu with a long list of items in tabular format on the left side of the screen. Selecting a tab opens another menu page where you can execute selections.

Press and hold the Enter/Mark key to get a waypoint of the boat’s current position. This brings up a data box with waypoint information that includes a symbol (there are 68 choices), a name that can be up to 10 characters long, a 20-character comment line, latitude/longitude, and a few other tidbits concerning the waypoint. The information can be modified. To change the name, you’ll need to scroll through numbers and letters, a slow and tedious process, but common in machines of this size. Symbols are chosen from a table on the screen.

Route entry can be accomplished using a text listing of waypoints or by selecting points on the map page. We used the map method to enter our test route. Once a new route is selected via the main menu route tab, the cursor and zoom function are used to compile a list of points that make up the route. Each time the cursor is placed and the Enter key is pressed twice, the unit makes a new waypoint and places it in order in the route list.

An easier way to enter a route, especially for a long trip, is to download Garmin’s free software from its website, build the route on your PC, then transfer the data to the 178C via a memory card.

Unless the map page data boxes are turned on, Garmin’s MOB function involves several steps and is not quick or easy to use.

One other noteworthy feature in the Garmin 178C’s bag of tricks is its ability to choose between north-up and course-up for the map page orientation; both worked well in our tests. It also features easy control of sounder functions like gain, zoom, depth range, and frequency through the use of an active cursor. We rated the Garmin 178C plotter/sounder Good for presentation and Excellent for ease of use.

Small-Screen Plotter/Sounders: Lowrance Bests Garmin and SI-TEX

Bottom Line: Gobs of functionality, first-rate screen resolution, and a simple-to-use sounder all in a compact unit that is easy to wire and install. The one caveat is the occasional screen overheating.

Garmin 198C
The 198C is new from Garmin. Standard equipment includes an external GPS antenna/sensor, an integral 500-watt sounder, and a dual-frequency transducer. The 198C has an internal world map and Garmin BlueChart cartography for the entire continental U.S., meaning U.S. operators need not spend extra money on a chart card.

The case is just over 6 inches high and wide and nearly 4 inches deep. Mounting and installation are similar to the 178C. However, one difference is the wiring for the external GPS antenna. A factory-installed connector on the display unit end of the antenna cable makes connecting it a snap but could hinder running the wire through a tight spot like stainless-steel tubing for a radar arch or binnacle. The 198C has tapped holes in the back of the case for flush mounting.

Our tester noticed slightly less detail on the 198C screen, which has a lower resolution than its little brother. The brightness control range (13 levels) was adequate and the contrast control was effective. Two color palettes, sun or dark, can be selected from the map tab on the main menu. In daylight, it showed some screen darkening when viewed with polarized sunglasses. Some intermittent screen fogging was noted in the center of the screen. We rated the screen Good for daytime and nighttime viewability. Pushbuttons and the cursor pad are backlit.

Function control, waypoint and route input, and manipulation on the 198C are the same as the 178C. The 198C, however, has fewer waypoint symbols (40), and they are displayed in a scroll-down list, not a table.

The map can be oriented north-up, track-up, or course-up. We tried them all. On one occasion while following, a course reversal in the course-up mode, the map failed to flip around and follow the boat path. Every other time it worked properly.

Comments found above in the 178C section about page display options apply to the 198C as well.

Sounder capability and functionality on the two Garmin’s are identical. We rated the 198C sounder Good on presenting data and Excellent for ease of use.

Bottom Line: You get more for your money with the Garmin 178C, in our opinion. We’d like the MOB process on both Garmins to have fewer steps and provide more useful information.

Lowrance 337C DF
Our test model was equipped with an external GPS antenna module, integral sounder, and dual-frequency transducer. Other models are available with internal GPS antenna, a single-frequency transducer, and a sounder that is a bit less powerful than the one tested. The Lowrance comes with a graphite gimbal bracket for mounting, which we used in our test. To flush mount, you’d need an optional dash mount kit. All the wiring connections on the Lowrance are made with easy-to-use, multi-pin twist-lock connectors. The only wiring we had to do was to power the unit and the National Marine Electronics Association (NMEA) 2000 bus. We noted one glitch on initial power-up: The display would not recognize the installed map card. We had to go into the menu and select the card to get it to work.

The 337C DF’s screen has the highest resolution in the group. Eleven levels of adjustment are available for both screen brightness and contrast when selected through the menu. Repeatedly pressing the Pwr/Light button sets minimum, maximum, and a middle-light level. We found the brightness level range to be adequate. On the other hand, the contrast control proved to be of little value. Moving the slider over the full range didn’t noticeably change the screen contrast.

Three different color palettes are menu selectable: high contrast, normal, and night. When viewed in sunlight with polarized sunglasses, the screen had some darkening, which increased when viewed from the side. The high resolution on the Lowrance screen brings the finest details into view better than any other unit tested. But because all test units had small screens, they need to be viewed from near rather than far. Viewing from a distance of 3 feet or less proved to be optimal.

Present position waypoints can be saved by pressing the Wpt key twice. Pressing the Wpt key once takes you to the waypoint menu where listed points are selected by name or proximity. The waypoint information page lists the symbol (42 are selectable), a name up to a 40 characters long, latitude/longitude, date and time, and bearing and distance. To modify any data, find the waypoint on the map, navigate to the waypoint, or delete it from the list, you simply select the action from the right side of the screen.

Build a new route by selecting it in the menu and then adding points from the map page. Move the cursor into position and hit the enter key to choose a point. Lowrance also has optional MapCreate 6 software and hardware to build and transfer routes from a PC to the 337C.

The Lowrance’s north-up and track-up modes worked well; course-up did not seem to function at all. According to Lowrance spokesman Steve Wegrzyn, the course-up mode works only when navigation to a waypoint has been selected. We were testing without navigating to a waypoint.

The Lowrance does not have a course predictor line like the other units; it only has a small, hard-to-see triangle showing the boat position and direction of travel.

The man-overboard function on the Lowrance is the best of any unit in this test. Pressing both zoom keys at the same time activates it. The unit then displays a text page with a compass rose, arrow to the MOB point, and every piece of data you ever wanted to know to help you get back to the MOB position.

Hitting the page key brings up a menu listing six map pages, six sonar pages, two navigation pages, and two status pages. The map/sounder split screen and data box selection on the full screen map or sounder pages are available here.

The high-resolution screen on the 337C had the best sounder picture of any unit. It draws finely detailed pictures of the bottom, and submerged objects that are easy to see and distinguish. We rated it Excellent for data presentation and Good for ease of use.

Bottom Line: Fine sounder detail, a high-resolution screen, powerful software, NMEA 2000 capability, and a reasonable price make the Lowrance our top pick.

SI-TEX ColorMax 6
We have tested the ColorMax 6 before as a stand-alone plotter paired with a SI-TEX CVS-106L sounder. This time, we used the ColorMax 6 to control and view the SI-TEX ES502 black box sounder. The SI-TEX can hold up to two C-MAP cards and can accommodate the new MAX card.

The ColorMax 6 comes standard with a quick-release bracket that allows easy removal of the display without fooling with any wiring or connectors—a nice feature, but the bracket is a little wobbly, in our opinion. Flush mounting is another option. With its black box sounder, wiring is more complex than on the other units tested. A number of small wires need to be connected from the display mount to the antenna and the sounder. Plus, the sounder black box needs to be mounted in a spray-free environment.

The SI-TEX has the largest screen in the field. Press the Power button to launch soft key control of the six levels of screen brightness and 11 levels of contrast. Using a combination of brightness and contrast provides ample control of the screen brilliance. Four color palettes can be selected through the map menu. The sunlight palette, which noticeably lightens the colors, improves the screen viewability in direct sunlight. Normal and NOAA modes are best used when the display screen is not in direct sunlight. The night palette darkens the colors to reduce glare and improves low-light viewing. When viewed in sunlight with polarized sunglasses, our tester noted a small amount of screen darkening. We rated the ColorMax 6 Excellent for both day and night viewability. Pressing the Enter key once brings up the create object menu. This allows the user to select Goto, Mark, Waypoint, or Range and Bearing. Marks are similar to waypoints, but their purpose is to allow the owner to flag sites not considered destinations, like an uncharted wreck, lost gear, or a dangerous shoal.

Selecting Waypoint, then hitting the Enter key stores a present position waypoint. The user points list—a directory of saved marks and waypoints—is retrieved by two presses of the Menu key and joystick selection of the page. Waypoint or mark names can be up to eight characters long, while one of 16 symbols in eight colors can be assigned to each point. Routes in the ColorMax are numbered, not named, but a descriptive 16-character note can be attached to the route. C-MAP’s PC planner ($179) can be used to plan a trip on a PC and then transfer the data to the plotter via memory card.

When you press the MOB button while using the full chart screen with no data boxes, you’ll need to manually select another page to get navigation data that brings you back to the MOB. Data on the map page can be displayed in one of three configurations: eight boxes, five boxes, or turned off for a full-page map view. Information in each data box is user-selectable. Split-screen formats on the ColorMax are limited to a map page/sounder split and a few sounder split screens.

To select the sounder screen from the map page, you must go deep into the menu system. The soft keys for the sounder—Gain, Noise, and Range—become active when the unit is displaying the sounder in full screen, or when the sounder is in the active window in a split-screen display.

One press of the Menu key brings up a long list of sounder functions. The sounder worked best in manual modes; auto gain and depth ranging did not work very well, in our estimation. We rated this sounder’s presentation and ease of use Good.

We found a package consisting of the ColorMax 6, the ES502 black box sounder, and a transducer for $1,087. Right now, purchasing a package like this would get the buyer a free C-MAP card.

Small-Screen Plotter/Sounders: Lowrance Bests Garmin and SI-TEX

Bottom Line: The SI-TEX package has a big screen coupled with a powerful sounder. Even with the soft keys, we found the chartplotter software less powerful and less intuitive than the other units.

We needed to be 3 feet away to properly read the charts or even the depth contours on these units. You can read a data-only pages (most have large block numbers and letters) from a greater distance, but these units are really meant for smaller boats or as backups to units with larger screens.

We like the two lowest-priced units the best, the Garmin 178C and the Lowrance. Both are compact, easy to install, reasonably priced, and were good performers. The Lowrance has the highest resolution and showed significantly more detail in bottom structure and all sizes of fish than any other unit. Add a bottom-lock feature and we’d be fully satisfied. The map showed good detail, too, and like the sounder it can be displayed on many easy-to-select pages. Still, we’d like to see an adjustable course predictor. Lowrance has the best MOB function and is NMEA 2000 capable (see “Talk Back” below).

The Garmin 178C’s resolution is second only to Lowrance. Sounder detail wasn’t as good either, but the active cursor makes the Garmin sounder easier to use. The 178C has the same features as the 198C, but for almost $350 less. Its occasional overheating is a concern, but we found that shading the unit, or better yet, mounting it in the shade, solves the problem.


Also With This Article
“Value Guide: Small-Screen Plotter/Sounders”
“Talk Back”

Also With This Article
• Garmin, 913/397-8200,
• Lowrance, 800/324-1356,
• SI-TEX, 727/576-5734,

Darrell Nicholson
Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 50 years. Supported entirely by subscribers, Practical Sailor accepts no advertising. Its independent tests are carried out by experienced sailors and marine industry professionals dedicated to providing objective evaluation and reporting about boats, gear, and the skills required to cross oceans. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser who has been director of Belvoir Media Group's marine division since 2005. He holds a U.S. Coast Guard 100-ton Master license, has logged tens of thousands of miles in three oceans, and has skippered everything from pilot boats to day charter cats. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida. You can reach him by email at