Multi-Function Display Installation
Project date: 2006

The latest in navigation instruments are the so called multi-function displays. What is a multi-function display anyway?

They are highly integrated system display units that typically include major navigation functions such as GPS, Chartplotting, Radar, Depth Finding, and instrumentation functions such as engine control, real-time video, weather satellite, and instrumentation from other sensors and devices.

The primary advantages of these multi-function systems are integration, real-estate, and cost.

Integration: Not only do the displays have the ability of providing information from a wide variety of sensors, information can be resolved that would not otherwise be available. For example, should fuel-flow information in gallons-per-hour from fuel flow instrumentation be input, a calculation from GPS information in distance traveled could result in the display of Miles-per-Gallon. This is only achievable because information from fuel flow rates AND GPS distance traveled were integrated.

Most of the multi-function displays meet NMEA-0183 and NMEA-2000 standards so that devices from other manufacturers can be interconnected. However, the degree of integration varies highly from brand to brand, and while theory suggests that Brand-A sensor should be read by Brand-B display, this is often not the case as there are still some compatibility issues. Some proprietary interconnections exist in multi-function displays as well. For instance, most display units are designed for a particular radar and sonar unit, as due to the high data throughput, a direct connection is required. This then means the MFD, radar, and sonar devices will likely have to be the same brand. This fact may influence your initial brand decision.



Real-estate: The available helm-space in most boats benefits from a single display unit that can provide overlapping display of many functions, such as Chartplotting and Radar, that otherwise would require two separate and discrete display units. Boats with limited helm-space can have this instrumentation without the boat owner needing to determine where to fit in all of the discrete displays. MFDs allow one display for everything.

Cost: Since a single display unit is required, individual functions, such as Chartplotting, depth sounding, and Radar become modularized, and all that is required is the purchase of the proper sensor package - often at a highly reduced cost - since displays do not have to be individually purchased for each function.

The chief disadvantages are redundancy, resolution, and Compatibility & Complexity.

Redundancy. If the display unit fails, all functions fail. This is in contrast to discrete units whereby if one display fails, only that function is lost. However, some multi-function displays have the capability of redundant operation, for those that have more than one helm.

Resolution: In this sense, determines the ability to display information simultaneously. Obviously, a single screen display does not have the ability to provide all of the information available unless the individual information sets become small, which may be hard to read. Multi function displays are best suited to display one or two main functions simultaneously, with paging used to scroll through display "pages" of other information.

Compatibility & Complexity. Although many devices are standards-based, a lot of proprietary devices exist, which limits their compatibility when using band A with brand B. Complexity is introduced as well because while the integration of instrumentation has seemingly infinite possibilities, the addition of each device increases the complexity of the overall system. Integration devices are not unlike complex computer networks and you do not want to have to hire an engineer to keep your boat instrumentation running.

With the arrival of a new technology, a new terminology is also found. The most significant is the use of the term "Sensor". When you desire to add a function to the display unit, you typically add the desired sensor. In this regard, a sensor can be anything from a GPS receiver, a Radar Transmitter/Receiver, or other device. In reality, this is not a bad conecpt, as it enforces the modularity idea of the multi-function display.

It is also very helpful to obtain a bit of knowledge in the area of interface standards, both industry standards, and any proprietary interface standards the equipment you wish to use may have. While an in-depth discussion of these standards is beyond the scope of this project, a brief description is in order.

NMEA 0183: The National Marine Electronics Association (NMEA) developed an interconnection standard in January of 1983 (hence 0183) that describes a data interface between equipment, not all that unlike computer modems. Equipment interconnects via 4 wires (2 transmit and 2 receive), point-to-point between two devices. However "NMEA 0183 hubs" can be used to expand the connections. For further information, review my NMEA-0183 White Paper

NMEA2000: The latest generation of interconnection, this is a bus technology, analogous to high speed computer networks. The bus technology means that many devices can be interconnected together in a row, and with the advantage of high-speed data transfer, much more information can be transferred between devices than can with the NMEA 0183 standard. NMEA 2000 is a relatively new technology, and new devices are appearing all the time. As of this writing, even Bennett - the trim tab folks - are making a NMEA 200 interface for their trim tab units. This allows the display of the trim tab position in the multi-function display unit (should it have that capacity). For further information, review my NMEA-2000 White Paper

Proprietary standards: such as Ray Marine SeaTalk, SeaTalk2, and SeaTalk HS are in reality quite similar to the NMEA standards, and often can be interconnected with NMEA devices with the proper cable or interface unit. They are typically based on the underlying NMEA standard, with the addition of propertiery information.

When you go about interconnecting sensors to the multi-function display, most will offer only one connection method.. However, some devices are capable of interconnection via multiple standards. For example, RayMarine's RayStar 125 GPS receiver can output either RayMarine proprietary SeaTalk, NMEA 0183, as well as RTCM simply by how the output wiring is connected. This allows the sensor to be used in a wide variety of applications. If you are not familiar with RTCM; "Radio Technical Committee, Marine" was a standard prior to NMEA-0183 that governed GPS connectivity. While RTCM's use today is limited, it illustrates the versatility of the RayStar 125.

There are so many choices for multi-function instrumentation and manufacturers that it is impossible to provide a comprehensive selection criteria for them. Rather, a single example will be provided, manifested in the form of a boat improvement project. Within this framework, a "rough sketch" of equipment selection is possible. In general terms:

Due to the expense of a complete system, as well as new NMEA2000 sensors becoming available, you will likely want to install your system in steps, to not only spread the cost out over time, as well as take advantage of new sensor products. This is the approach we will be taking. We'll start out with the basic system of a GPS Chartplotter, then expand from there with future additions.

Selection of the Multi-Display Unit, GPS receiver, and Radar Sensor.

For my display unit, I selected a RayMarine C-80 display. RayMarine offers three sizes of display, and the C-80 was the best fit for my helm. RayMarine also offers C-Series Wide, as well as an E-series, however it is considerably more expensive. The advantages of the E-series includes the ability to display data at two helms, as well as enhanced chartography and sensor support. Since I have a single helm on my boat, I felt that the C-80 was the right unit for my needs.

RayMarine C-80 Multi-Function Display                    RayMarine RayStar 125 GPS

One word of caution needs to be given here. You can spend your retirement savings on one of these units, so take some time and pick the right unit for you. RayMarine is only one of several manufacturers that make these systems, so my choice should be no way an endorsement of any kind of one brand over another.

To build a minimally functional system, you will also need a GPS receiver as well as a chartography card. While you can technically get by without the cartography card, the system would not perform up to its potential - that you paid for.

The latest trend in GPS systems is to integrate the receiver at the antenna. An alternate technology still exists, and can still be found on stand-alone chartplotter systems, is to have a remote antenna, with the GPS receiver in the display unit. This results in some signal loss due to the coax cable between the receiver and antenna. However, with the receiver built into the antenna rather than the display unit, the performance of the GPS system is enhanced, due to the lower loss of not having to feed the signal down a coax cable. I selected a RayMarine RayStar 125 GPS unit.

Typical Open Array Radar Sensor                                     Typical Radome

One topic worthy of discussion is the selection of the radar sensor itself. There are two styles you will encounter; an open array, and a radome. The chief difference between them (other than cost) are range and resolution. Range is somewhat a complex argument. The manufacturers will typically state a range from 25 miles or so up to 80 miles, depending on the antenna configuration and power. However, if you are scanning the sea surface at the typical height the radar is mounted on a pleasure boat, it is impossible to have a range of 80 miles as the curvature of the earth will limit the range to 12 or so miles. However, high flying objects as well as weather will be detected at a further distance. Does this mean a 10Kw unit is no better than a 2Kw unit? Not necesarily. There are two primary advantages to a higher power unit. The first is resolution. While a 2kW unit may detect two boats setting together at 5 miles out, they may show up as a single blip, whereas the higher power unit may show each individual boat. This is purely a function of the radar's power and the width of it's antenna.

The second advantage is Fade Margin. When the radar's electromagnetic signal goes through space, it is attenuated. The attenuation results in the signal becoming constantly weaker the further it travels from the antenna. The "range" of the radar as specified by the manufacturer can be considered the maximum distance the signal can travel (and bounce back), accounting for this loss. Of course, this would be in ideal conditions. However, the loss of signal is not constant, as environmental factors such as atmospheric conditions affect the rate of signal loss.

As it turns out, fog tends to scatter the antenna's energy sufficiently to reduce the range of the signal. Therefore, a 2Kw radar with a 24 mile theoretical range may be reduced to 12 miles distant in a fog. The difference in maximum to minimum distances due to atmospheric conditions is known as Fade Margin. Obvously, a more powerful radar, while also exhibiting a loss in fog, would not affect the usefulness of the radar as much, so it would have a higher degree of Fade Margin than a less powerful system.

Disadvantages: While a more powerful unit is a better performer, the disadvantages are cost, and increased danger from radiation. Cost is factored for both the cost of the radar sensor as well as upgraded power wiring required for it's operation. Since the radar is more powerful, it must be mounted further away from humans to minimize radiation hazards.

Radar units are available in either open array or radomes. Open arrays are higher performing since the width of the antenna is greater; the longer, the better. Radome units also have a rotating antenna, but it is contained within the radome itself. This can be an advantage for sailboats as many radomes are mast-mounted, and the mainsail is less prone to fouling on a radome.

For this project, I am using a RayMarine RD-424 sensor, which is a 4Kw 24" dia radome.


Suggested updated units.


Chartplotter function. Multifunction Display Units typically come with high-level mapping, but no detailed areas. You will need to purchase the desired chartography chip for your location. The good news is that many of the chips today cover a wide area, so there is a good likelihood you will not have to swap chips, unless of course, you are running the Great Circle route.

RayMarine C-80 in action

Display unit Installation

One decision to make is how to mount the display - Gimbal or in-dash flush mounting. I prefer in-dash mounting, but it does take more time and effort to do so. However, some boats may not have sufficient dash space for flush mounting. If you have the choice, check with your insurance company - some policies may not cover any electronics that are not flush mounted. When flush mounting the display, depending on brand, you may have to purchase an optional flush-mount kit from the manufacturer. However, the C-80 display included a flush mount kit.

When looking for a suitable location, keep in mind that connections and wiring will exit the back of the unit, so be sure to allow for that additional space requirement. Check with the installation instructions to determine if there are any special dimensional requirements, such as minimum distances for air flow, distance from a compass, and so on.

So we've determined a suitable location, and we're ready to cut. Well, not quite. I always like to use the phrase "Think Twice, Cut Once", which is my version of the cliché "Measure Twice, Cut Once". I just think this has more application here. You want to think about what you are doing; have you thought of everything we have discussed here? location, clearance, and the ability to access the unit from the rear?

Go through the installation instructions if you need to - step by step - in your mind, so that you do not forget anything. It is very difficult to patch a big hole in your dash, so be sure you have thought about everything for awhile.

After "thinking twice", its time to cut. I always like to layout my cuts with "blue tape" and a permanent marker. This not only allows you to layout where to make the cut, the blue tape protects the underlying surface from scratching. If possible, remove the panel when you make the cut. Panels are typically made with some amount of aluminum in them, and you want to minimize the metal shavings that get thrown in to the backsides of your switches and gauges.

If you cannot remove the panel, use blue-tape and cover up both the front and back of all of the nearby switches and gauges. Another tip is to run a shop-vac while you are cutting to suck up all of the shavings. Having an assistant is really helpful here. Enlist your better-half, they just might surprise you and pitch-in with the project.

My instrument of choice for making cuts is a jig-saw adapter for a Dremel rotary tool. I have also had good luck with a small pneumatic reciprocating saw, but this requires an investment in an air compressor, and the ability to get the compressor on site. If you use the Dremel approach, note that you are at the limit of the tool here, so take it slow, take it easy, and let the tool cool down periodically.


If you drill a pilot hole (larger than the diameter of the saw blade) at each corner of the cutout, you will not have to negotiate any sharp turns.

Once the cutting is finished, you will likely want to go around with a file and clean the cuts a bit. If it looks a bit ugly - that is OK, as long as you did not go outside of the lines; nothing will show after you install the display.




You may find that you will have to test fit the display unit a few times, then trim here and there to get the right sized hole. Although a cutting template is provided with the display unit, I have found that they typically just get you in the ballpark.

When fitting the display unit to the helm, you may need to re-route nearby wiring to ensure proper clearance of the display unit. As shown here, there is plenty of obstruction-free room for the connectors. As you tighten down the display unit, especially if you flush-mount it, take special care that you do not "warp" the case. Although many dash panels look flat, they often have a slight bow to them, as was the case with my system. Fortunately, the dash consisted of an aluminum over fiberglass affair, so I was able to simply slide a washer in between the aluminum and fiberglass, which flattened out the aluminum. A tip - superglue the washers to the underside of the aluminum so that they won't fall out.

The gap shown above is accentuated to bring out the point that the dash plate is often not quite straight and true. Often a single washer is all that is required to bring the dash into alignment.

The installation of the GPS receiver and radar radome were covered in the Radar Arch article, so it won't be repeated here. However, the interconnection of the GPS receiver to the multi-function display is accomplished by connecting the GPS SeaTalk port to the display SeaTalk port via the terminal board strip shown by the yellow circle. You may recall that this mounting board was part of the wiring upgrade done at the helm in a previous support project.

As shown on the left, the RayStar 125 has 5 connections. Note that it supports NMEA-0183 and SeaTalk. For this project, the RayMarine C-80 display unit has three connections; SeaTalk, NMEA-0183, and NMEA-2000 (SeaTalk 2). Since I have other plans for the NMEA-0183 and NMEA-2000 networks, I'll be using the SeaTalk to direct connect the GPS to the display. The connection to the SeaTalk network is shown on the right; however, consult with the installation manual for your application.

The radome connector is directly plugged into the back of the C-80 display unit.

In addition to the SeaTalk interconnection, the main DC power wiring is also connected to the board's fuse block, as well as to the ground grid strip. The 4KW radome will be powered through the display unit, so use the appropriate wire size and fuse to make the connection.

Some radar units, especially the higher power open array units require a separate power connection. That is, the RayMarine 2Kw and 4Kw radomes receive power through the display unit, while the 4Kw and 10Kw open array units require a separate power connection. Of course, this will also vary with other brands of equipment.

After connecting the GPS receiver and power leads, all that is left to do is to insert the cartography chip and turn the power on. Typically there are some setup tasks to do the first time the unit is energized, but this varies with the unit.

Also, quite often, there are firmware upgrades that should be applied to the unit. For instance, the C80 is a 2004 product. In later years, RayMarine added an engine control display enhancement, AIS support, and other features to the product. All that takes to add this function is a firmware upgrade - available free from RayMarine. Again, this is only an example; other manufacturers may offer similar upgrades.

(Click on the drawing for a full sized version)

The project at this point is considered to have the base foundation. In future installments, we will be adding components to this system until we have our desired configuration.




Home    Return