In the December 1998 issue we covered the latest crop of handheld GPS devices and were impressed with the many capabilities of these units. What, then, is the appeal of a fixed-mount unit?
First, using onboard power enables you to keep the unit on constantly, making available a complete navigation track history. While this is also possible with portable handheld units, you don’t have to worry about fumbling around with external power cords and finding connectors. Turning portables on and off to save battery power only tells you where you are at that moment, not a track of where you were while the unit was off. A saved track history can be extremely valuable for return or future trips.
Second, handhelds generally have significantly smaller screens and fewer buttons compared to most fixed units, which can make them more difficult to use and to interpret.
Third, the design and mounting of the amplified external antenna on fixed-mount units inclines one to locate it in the most desirable location where its signals won’t be blocked. Fixed-mount units also have the internal room to accommodate a built-in differential beacon receiver (normally available as an option) for DGPS. This is more desirable in terms of cost, accuracy and dependability than adding all the extra wiring and boxes that come with a separate differential unit.
Lastly, most fixed-mount units have more flexibility for integrating with other navigation gear, especially when multiple ports are required, such as an autopilot and a chart plotter at the same time, or even a Loran C unit. And, some boat owners may already have a separate chart plotter and not want to spend the extra money duplicating hardware.
Though the integration of chart plotters and GPS units is becoming more and more prevalent all the time, in this article, we look just at stand-alone GPS units without cartographic capabilities. In a future issue, we will evaluate the much more expensive integrated units that incorporate chart plotters.
What We Tested
We tested five very different units that gave us a good cross-section of what is available. Their prices vary considerably, from about $300 to $1,800 at discount. It is impossible to fairly compare one price extreme to the other, so we will go to some lengths to point out the virtues and vices of each unit, and make some recommendations as to value for the price.
Accuracy Variables
GPS receiver accuracy is affected by several variables, but most of the error can be attributed to Selective Availability (SA). Because the US government plans to employ Selective Availability (intentional degrading of the GPS signal) for at least the next several years, the best position accuracy one can expect is 100 meters or better 95% of the time, 50-meter accuracy or better 65% of the time and 40-meter accuracy about 50% of the time. Because of SA, no particular civilian unit (notwithstanding differential GPS) is capable of greater accuracy than these government established statistical baselines, although worse or variable accuracy is certainly possible. The effects of SA can be nullified by adding a differential beacon receiver, which improves accuracy to about 5 meters or better. Differential GPS signals, at a minimum of about $400 for the receiver, are currently available in most US coastal regions as well as on the Great Lakes and Mississippi River, and in over 20 other countries.
Another factor affecting consistent accuracy is the number of channels in a receiver. Under perfect conditions, 12 parallel channels are unnecessary; however, because eight or more satellites may be in view at any given time, it’s possible for some satellite views to be blocked or partially obscured by a boat’s own rigging, other boats or shore obstacles. In our tests, this is where the 12-channel units seem to have an edge, because they are able to optimize existing geometry for the greatest accuracy possible while reducing or eliminating temporary loss of signals from obstacles or while maneuvering. (A harbor full of masts or large boats, or surrounded by buildings, can play havoc with GPS signals). This improved accuracy shows up as improved “Estimated Position Error” values given in estimated feet off the mark. Other GPS sets use an HDOP (Horizontal Dilution of Position) value where a value of 1 is perfect and 6 is marginal. Having these estimates gives you better confidence in the accuracy of your position. Nonetheless, we do not rule out the eight-channel units, as some excellent values and features are to be found among them.
Where Does Loran Fit In?
Until recently, Loran C appeared to be not long for this world, but it has received a US governmental reprieve until at least 2008. Apparently, the large number of Loran users has influenced the decision makers, so those of you with Loran receivers don’t have to hang up your lattice overlay charts just yet.
While on the subject of Loran, the use of Loran waypoints in GPS units needs to be addressed. Some of the GPS units tested have the ability to accept waypoints in the Loran format (GRI and TDs), which are then converted internally to usable data points in the GPS. Be very cautious in doing this as there are several pitfalls due to the fundamentally different ways in which GPS and Loran obtain position fix data. The Raytheon and Northstar units allow for simultaneous inputting of Loran C signals for a choice of display information. This allows for system redundancy (where Loran is available), and superior position repeatability, which is a benefit of Loran C. Once you have been to a particular spot, returning via Loran C can be more precise than with regular GPS.
How We Tested
All five sets were subjected to both bench and field tests which took place along the Potomac River as it flows into the Chesapeake Bay. Checked were listed specifications such as time from start-up to position display, power consumption, screen readability, etc.
Accuracy was established in two ways. First, each unit was checked, while stationary, with an unrestricted view of the sky to establish basic maximum accuracy parameters. Next, the units were field tested near boats and shoreline trees as well as rising terrain. All units were tested simultaneously to reduce the effects of external variables such as varying SA values, movement of nearby boats, etc.
User friendliness was evaluated based on the features of a given unit and how easy they are to access and use, i.e., whether excessive menu scrolling is required to access common functions, or if the general layout is conducive to ease of use or, conversely, if it promoted errors. We consider using one button for several functions to be less desirable than dedicated, single-function buttons, especially in fixed-mount units where space is not so critical. The same holds true for requiring multiple sub-menus to carry out common operations.
Another desirable characteristic, in our opinion, is the ability to easily customize various displays to suit one’s own particular requirements. At the same time, an excessive number of options can be confusing.
Other criteria include screen size, resolution, information presentation and readability.
The Common Thread
A number of important features are part of each of the tested units; to avoid redundancy they are noted here.
All of the units displayed acceptable and consistent accuracy in the stationary, unrestricted sky view test.
All units can interface with a PC via the use of a proprietary interface cable (generally not included). All units can interface with other navigation/instrument systems, but some with more than one item at a time. The most sophisticated have multiple and independently configurable NMEA data lines.
All can be purchased with differential GPS built in or are able to accept an add-on differential receiver.
All have acceptable screen readability in bright sun and at night and are adjustable for brightness.
All have setable alarms for functions such as anchor drag.
All have a simulation mode for practicing at home.
There are many differences, however, which we note in the following individual unit evaluations as well as in the Value Guide on page 28.
Furuno DG-30
This is a nicely made, basic, eight-channel receiver that is very easy to use and provides just about every GPS navigation needed. It did not fare quite as well as the 12-channel units in difficult sky view conditions because it had significantly greater HDOP values in the moving tests with partial sky obscuration. And sometimes it was unable to lock up enough satellites for the 3D mode. (The Furuno needs HDOP values lower than 4 for 3D mode.) It also occasionally lost lock on satellites for several seconds at a time.
Considering its low price of about $309, however, there are several things to like about this unit. The screen is easy to read, even at some distance, and it has continuously adjustable lighting to tweak night screen illumination to exactly the level desired. There is not an abundance of keys, but they have a good feel, their use is intuitive, and you are not overwhelmed with menu choices. A lot can be said for keeping all the needed functions while not getting carried away with excessive customizability.
Noteworthy was the lack of glare on the lime-green screen, which improves its useful viewing angle.
The DG-30 comes complete with a mushroom antenna and 33′ of cable.
The manual is complete and has good installation and wiring instructions.
Another feature we like is the dual NMEA outputs, enabling two devices to be hooked up simultaneously, such as a chart plotter and an autopilot (providing they speak the proper NMEA dialects). A potentially valuable feature for owners with lots of Loran C coordinate data to move to their GPS is both Loran and Decca TD input modes. However, the DG-30 does not accept live Loran C receiver data.
Bottom Line: At about $309 discount, the Furuno DG-30 is a good value for someone looking for a low cost receiver with the special features described above.
Garmin 126/128
The $280 Garmin 126 has a built-in antenna, whereas the identical and slightly more expensive Garmin 128 has an external antenna and 30′ of cable. It is the low-priced unit to beat due to its consistently outstanding performance even under less than ideal reception conditions.
The case is waterproof to IPXE-7 standards, allowing total immersion to 1 meter (best in test).
There are buttons for feature groups so using the 126 is quite easy. The need for menu scrolling is lessened, but not eliminated. There are three levels of lighting intensity adjustment, which proved adequate in testing.
The navigation screens are very customizable. We especially liked the track-back function, which allows you to reverse or save a course without having to reinsert waypoints manually along the way. This feature is limited to 30 automatic waypoints, so for extended trips some manual inputting may be required.
Another excellent feature is the ability to orient the screen to one of three choices (north up, track up or course up).
There are abundant alarms, including nine proximity alarms with independent settings in which you can establish an alarm “circle” around each waypoint.
Also, you may assign up to 16 symbols to waypoints. This helps to keep things uncluttered, as the screen resolution is the lowest of all tested models. It is, however, adequate.
In selecting navigation screens, Garmin gives the user a choice of either a highway or a compass rose page, depending on your personal preference. If you want to bring up the nine nearest waypoints from a given position, a button press brings them up for quick and easy navigation-faster than a plain “go to” function.
The most time-consuming and somewhat frustrating operation was having to enter waypoint data via the slewing method-scrolling through all letters and numbers one character at a time (although it is possible to upload information via a PC). The only other problem we had was with the case antenna mounting plug, which was molded not quite right and prevented us from properly locking the antenna cable. Nevertheless, the unit worked fine.
If you wish to take advantage of the many ways in which information can be customized, you’ll have to spend some time studying the manual.
Bottom Line: We applaud Garmin’s relentless pursuit of continued software improvement in already outstanding units, and to offer them at such competitive prices. The 126 has many terrific features, performs well, and is priced low. It is our Best Buy.
Lowrance Global Nav 310
Great things can come in small packages, as does this diminutive, inexpensive, strong-performing GPS. List price is $299, but at press time the 310 was too new to have appeared in discount catalogs. The Global Nav 310 was our smallest test unit-even the antenna cable and fitting are half the diameter of other models.
The 310 is feature packed as well as having the easiest interface to master of the lower cost sets. You can customize screens to your heart’s content, even to the point of putting the CDI scale on any of 15 screen display options. Resolution is on a par with the Garmin but Lowrance takes a different approach to the data display, making larger characters. However, you can still place up to eight digital data items in a navigation window.
Lowrance uses a nifty compass rose (with or without four data items) as its navigation display, but does not have the additional highway page option that the Garmin has. We particularly like the plotter screens which have the same three orientation selections as the Garmin. And, if desired, grid lines may be placed on the plotter screen. There are 34 zoom ranges available to view a string of waypoints (no map), including seven ranges between. .1 and 1 mile. It keeps the screen from appearing cluttered, while still giving maximum detail. The plotter can zoom all the way out to 4,000 nm, far beyond any other unit-if that’s of value to you (most of the others only go to 320 miles).
The zoom keys work from the movable cursor position, as opposed to present position, so you can zoom in on any detail while navigating a route plan without disturbing the setup. There are also a total of four cursor keys and eight data entry/function keys. Notably absent is a MOB key, although a current position can be quickly saved with a few key strokes. This unit has additional terrestrial functionality, both software and hardware. It has a military grid system in its database. A magnet mount antenna is included in addition to the marine pole mount.
Bottom Line: Garmin still gets the nod in this price range, but your needs may be different, so we advise that you examine the Lowrance 310 first hand if low cost, small size and customizability are high on your list.
Northstar 941X
At $1,730 discount, what makes the US-made 941X worth several times the cost of, say, the Taiwan-made Garmin? Primarily, it’s the hardware, which includes a large, high-resolution screen similar to a mini laptop computer (320 x 240). This allows for an extremely clear display packed with information, such as 30 waypoints viewed simultaneously. Add to this a vast array of dedicated function keys, a cursor key, five soft keys which change function depending on which screen is displayed, a keyboard that dramatically reduces data input chores, and you start to see why this is an expensive unit. The data cable has no less than 17 wires for integration with other electronics as well as an additional 10-wire auxiliary cable for future use.
Extremely well-integrated software allows you to use the unit effectively after only a brief review of the extensive manual-easier than any other unit despite the vast array of features. Screen prompts and soft keys dedicated to particular screens aid this process and preclude the trap of having too many menu levels. There is not an excess of screen views because the customizability and available data are all there on the big screen; not much flipping around is necessary as on smaller screened units.
There is a 2D or 3D display oriented with heading up. Steering sensitivity can be easily changed from tenths of a mile to feet or meters-primarily valuable for differential GPS use. The plotter screen is excellent, with a user-selected lat/lon overlay display. Avoidance waypoints may be displayed as adjustable diameter circles, which give you a truly graphic feel. We found the display much less abstract than the smaller, lower resolution screens. Functionality and capabilities abound. The 941X’s waypoint and route capability is huge. Waypoints may be viewed or displayed in a number of different ways. On arrival at a waypoint, you can even recalibrate it for greater accuracy. While this can be done with the other units, it’s eminently simple on the 941 and includes Loran TD information taken from lists or charts. Loran data may be fed as live information from a compatible Loran receiver. There is even a graphic display of tide tables through the year 2010.
The Northstar has extensive integration capability with other electronic hardware, including mixed brands. Even the old NMEA 180 format is available to work with 1970’s-era autopilots. The unit can simultaneously drive two independently configurable NMEA ports in addition to the RS 232 port. The separate auxiliary port provides further configuration possibilities. All the wiring data is available on-screen at the touch of a few buttons. Additionally, while we were not testing differential GPS units, we found the differential GPS in our test unit (actually, we had the 941XD) to be exceptionally well integrated, as well as having two-channel capability, which provided for totally automatic operation if desired-no manual frequency inputs required.
Is the 941X the perfect unit? No unit ever is. We can quibble with the use of RG-59 cable for the GPS antenna, which has a solid center conductor; a stranded cable would be our choice for vibration resistance. We would also like to see a dedicated MOB key rather than one shared with the Save key. In a MOB situation, the key must be pressed and held for three seconds to initiate the MOB function. In a first-class unit like this, an external alarm capability would be appropriate. Lastly, the unit has a slick manual waypoint function to easily insert temporary waypoints while en route. However, we would like to see the addition of a fully automatic Garmin-type automatic waypoint insertion option.
Notwithstanding our quibbles, this unit sets a benchmark at the high price end for quality, versatility and ease of use. If you want even more, add differential GPS (designated the 941XD) or chart plotting (951XD) to the same basic unit.
Bottom Line: What a piece of hardware! This is a first-class GPS which would be at home in a million dollar luxury yacht, particularly with Northstar’s superlative integration capability with other electronics.
Raytheon Nav 398/GPS 112
Raytheon takes a different approach to GPS. They embed a 12-channel GPS receiver in the antenna housing in a weatherproof enclosure and call it the GPS 112. The Nav 398 is only a display terminal which can receive inputs from GPS, differential GPS, Loran C or Loran TD info from a waypoint list or chart.
The Nav 398 is equipped with a proprietary, bi-directional data format called SeaTalk. This format communicates navigation information between compatible Raytheon marine products and Autohelm instruments for a tightly integrated information communication setup. And there is a provision for standard NMEA data communication with other electronics as well as an RS 232 pair of wires. Specifications guarantee that at least two compatible NMEA devices can be driven in parallel, with the possibility of driving up to five “modern” (meaning low-power consumption) NMEA devices. Because only one pair of wires is available for NMEA devices, independent simultaneous configurations are not available as they are with the Northstar.
The display screen is about the same size as the Garmin and Furuno, but has much higher resolution (240 x 240), so it seems larger in terms of image perception. Information is easy to read and customizable both in content and screens displayed. It’s fun to use. There are 15 buttons to control functions, but no separate cursor control. Data entry and functions are much easier and quicker to input than the Garmin and Furuno units. If you think scrolling bugs us, you are right. It’s probably a necessary evil in handhelds, but we like more direct control in a fixed-mount unit like the Raytheon or Northstar. For example, the Nav 398 has a direct plotter key for a one-button push rather than scrolling through navigation screens la Garmin. Very nice. Three of these keys also serve as soft keys under certain display conditions to make functionality that much easier. It’s not as simple as the Northstar, but conceptually similar. We distinctly like the dedicated and specially colored MOB key that activates a specific MOB navigation program. With no shared keys, no special button presses required, it’s simple.
If there is any concern with this unit, it would be with the limited track point memory, which at 300 points is only one-third the memory size of the other units. Track points can optionally be laid down on all these units at different intervals to show the route history of your trip. (Garmin is the clear winner, both in track point memory as well as functionality.) It is an adjustable function (time or distance) and probably would only be of concern in long, many-segment trips in which you are trying to keep an accurate track point memory. Also, unlike the other units, there is no provision for adding a comment about waypoints entered into memory. An eight-character name and/or symbol is available, which is probably enough for most people.
Bottom Line: Considering features such as Loran C receiver, and Loran TD waypoint input, for the price there is a lot to like about this unit. It has flexibility and is the perfect choice if you have other SeaTalk-capable electronics or instrumentation.
Conclusions/Recommendations
You can see that there is a lot to consider in selecting the GPS unit best suited for your specific needs. In the chart, note the difference in power consumption of these five units, which ranges from 3 watts to 12 watts.
If cost is your primary consideration and there is no Loran legacy information to deal with, the clear choice is the Garmin. It’s inexpensive, full featured, customizable to the extreme and works well under adverse reception conditions.
The principal appeal of the Lowrance is its low cost, high degree of customization and small size.
The Furuno is attractive if you have lots of old Loran or Decca waypoint information which you would like to use, or just want a basic, easy-to-use GPS. Alternatively, if you have a PC and lots of valuable TD coordinates, a software program called The Loran and GPS Vault makes these conversions for uploading and much more. Price is $50 from Point Systems (888/764-6879.)
The Raytheon Nav 398/ GPS 112 provides a great deal of flexibility in integrating both active Loran input data as well as legacy waypoint data in TD format. The increased number of push-buttons as well as function-driven soft keys enable quicker data input as well as one-button access to most navigation functions, which makes operation faster and easier than “key-challenged” competitors, which depend more on menu scrolling.
The Northstar is simply the result of saying “what if I want just about everything?” in terms of functionality, ease of use and integration. Unfortunately, “everything” will cost you about $1,800 at discount prices for basic GPS. The 941XD with differential will set you back $600 more. But if you can afford it, what a way to go!
Contacts- Furuno USA, 271 Harbor Way, South San Francisco, CA 94080; 415/873-9393. Garmin International, 1200 E. 151st St., Olathe, KS 66062; 913/397-8200. Lowrance Electronics, 12000 E. Skelly Dr., Tulsa, OK 74128-2486; 918/437-6881. Northstar, Technologies, 30 Sudbury Rd., Acton, MA 01720; 978/897-0770. Raytheon Marine Co., 676 Island Pond Rd., Manchester, NH 03109-5420; 603/647-7530.
