Starting a dialogue

Today’s marine electronics provide remarkable levels of performance, utility, convenience and value. Even quite small boats can now be equipped with navigation suites that would have been out of reach for all but the megayacht fraternity only a few years ago.

A level of value and increased performance is possible when systems are interconnected so that they can exchange information. A short while ago, we upgraded portions of the electronics suite on our boat, with the addition of a Yeoman electronic chart table, Furuno 1832 radar, ACR RapidFix EPIRB and a Tecnautic autopilot. The boat is also equipped with Furuno GPS 35 and GPS 36 units, a KVH sailing-instrument system, Ross DSC500 class-A VHF radio, SEA 235 high-frequency/single sideband and Macintosh PowerBook 1400 cs (upgraded with a 400-MHz processor and 20-gig hard drive) running Navimac software. Installing the new equipment, including the hour spent in the bosun’s chair halfway up the mizzenmast, was the easy part. Getting all of the devices to talk to one another was the most time-consuming part of the job.

Two-way data interchange is required between the Furuno GPS 36, the Ross DSC 500 VHF/DSC radio transceiver and the Yeoman chart table. One-way GPS data flow is needed for the autopilot, the radar, the laptop computer and the 406-MHz EPIRB. Two-way data exchange between the GPS and the radar is optional and can be useful by allowing a point designated on screen with the radar’s cursor to be uploaded as a waypoint for the GPS. Supplying ship’s heading information from the autopilot’s rate gyro-equipped heading sensor to the radar enables a number of useful radar display options. The Tecnautic autopilot accepts apparent wind angle information from the KVH instrument system so that it can automatically sail at a constant relative wind angle.

The system interconnect project was somewhat complicated by the physical location of many components in the cockpit coaming storage compartment that houses the VHF/DSC radio, GPS and the autopilot control. As a result, most of the system interconnections had to be made in the constricted space in the coaming compartment. The need to route data from that compartment to the mid-cockpit table that supports the radar added a challenge to the project. The installation challenge was justified by our strong belief that all the navigation equipment should be visible and operable from the helm. Additional data connections at the chart table allow the Yeoman and the laptop to be used for voyage planning in air-conditioned comfort, a special consideration in the boat’s usual Florida and Caribbean voyaging grounds.

Connection sense

Providing GPS information to the EPIRB is clearly desirable. Should you ever have to activate the beacon, the search-and rescue folks won’t have to wonder for a moment about your precise location. Ask any search-and rescue professional and they will tell you that the first hour of any search exercise is the most critical. Sending GPS position data to the VHF/DSC radio provides a similar advantage, should it become necessary to send a mayday or another type of urgency call. The DSC message will provide anyone receiving the transmission with your precise location. This communication link can be extremely valuable in routine communications. It will allow vessels to exchange position information, for example, to automatically provide your position to a ship or other yacht alerted with an “all-ships” or “geographic” call. Position data from the VHF/DSC radio on another vessel sent to the GPS navigator can become a waypoint for navigation purposes.

The interface requirements for the Yeoman chart table are similar in function to those of the VHF/DSC radio. Providing a two-way data flow allows the vessel’s GPS position to be precisely located on the chart, and waypoints defined on the chart with the Yeoman’s mouse can be uploaded to the GPS.

Interfacing the GPS and the autopilot’s heading sensor with the radar is important. This changes the radar from being simply a target detection device to a multifunction display. When in standby mode, the radar screen will display the vessel’s position, heading, course and speed over ground, the bearing, time to go, and estimated time of arrival at a navigation waypoint. Connected to suitable transducers (not installed on our boat), the screen will also show water depth and water temperature. When the radar transmitter is active, the GPS data enables display of the active waypoint. Heading information from the autopilot provides a number of useful display options in addition to the conventional bow-up display. These include heading-up (with the vessel’s heading shown on-screen), north-up, course-up or true motion. The choice of display modes can greatly simplify interpretation of radar information. With two-way communication between the radar and the GPS, it is possible to transfer the latitude/longitude coordinates of a radar target identified with the cursor to the GPS for use as a waypoint.

Defining the desired interconnections was not difficult. After all, two-way data exchange using NMEA 0183 usually requires only three wires: send, receive and common ground. In this instance, the most difficult part of the job was dealing with the fact that each equipment manufacturer is free to choose the wire color code for each function independently, following no single standard. A number of units used yellow to designate NMEA data out and blue for common or ground, with green used for data input. However, other devices used entirely different color designations. Devoting time to decoding the color matches will save countless hours of troubleshooting later. A degree of complication can occur when individual manufacturers use somewhat different NMEA sentences.

The mechanics

Once the interconnect diagram was in hand, the next step was to decide on the mechanics of making the connections. Since most of the interconnections would reside in the port-cockpit coaming cuddy compartment, they would have to be protected from the elements as well as being accessible, both during initial installation and for possible later modification. (Do electronics ever remain the same for long?) As usual, the local RadioShack provided a useful source for the bits and pieces needed. Power connections were made using conventional barrier strips in conjunction with crimp-on terminals. Multiple-point, European-style terminal strips designed to work directly with the stripped ends of small-diameter, stranded insulated wire were used for all signal interconnects.

The terminal strips were fastened to the lid of a plastic box using 3M’s exterior-grade, very high bond, double-sided, foam-core adhesive tape, eliminating the need to drill holes for mounting screws for the terminal strips and avoiding the need to seal screw holes against the entry of water. The tape has remarkable holding power and was used throughout the boat. Mounting the terminal strips on the lid of the box allowed the wiring process to proceed without interference from the sides of the box. Once all of the connections were made and verified, a slot just large enough to pass all of the cables was cut into the side of the box. Silicone sealant was applied to reduce the likelihood that water entering the cuddy compartment would find its way into the junction box. The plain steel screws that come with the box were replaced with stainless screws. The box was fastened in place with a couple of strips of self-adhesive marine-grade Velcro hook-and-loop fastener.

One of the major challenges in doing the wiring was the need to deal with the very small-size wire now common in much electronic equipment. Stranded wire gauges smaller than 22 AWG (American wire gauge) are being used for some equipment interconnections. Stripping this size wire, without breaking some of the fine strands, can be a challenge.

Once the interconnect job was finished, the result has proven very satisfactory and well worth the effort involved. Everything talks to everything else quite happily. When sailing, the GPS and VHF/DSC carry on their usual dialog while the autopilot listens to its heading sensor, the GPS or the wind system. When needed, the radar is brought up from its storage place in the aft cabin and locked to the cockpit table where the power, radome interconnect and data cables (heading and GPS) are readily connected. The Yeoman usually remains on the chart table below. The GPS constantly updates the EPIRB via its infrared diode link. When exploring unfamiliar areas, the laptop computer is connected to the system so that GPS-derived positions can be logged into the chart program, providing a useful record for later playback in addition to the data recorded in the Furuno GPS 36-track memory.

There is no doubt that future developments in marine electronics will bring even more opportunity for worthwhile inter-system communication. Fortunately, the interconnect process will become easier with such protocols, such as NMEA 2000 and Ethernet, as used in Furuno’s NavNet equipment. These two systems will likely become complimentary, with NMEA 2000 dealing with low data-rate information and Ethernet providing the means for exchanging higher-speed data. Bluetooth, a new wireless, self-organizing, short-range system will likely find its way onboard. You will be able to sail along, enjoying Nature’s world, while your electronic servants hold an intense, ongoing discourse.

Contributing Editor Chuck Husick, based in Tierra Verde, Fla., writes frequently on all aspects of marine technology.

By Ocean Navigator