Electronics, GPS and VHF, Part 5: Infrastructure for VHF and Digital Selective Calling

The VHF and terminal block (for DSC integration with the GPS), dry-fitted into place
DSC, or Digital Selective Calling, is a faculty or a capability that is dependent upon the integration of a GPS and VHF radio. For a number of years now, the United States Coast Guard, through a series of land-based towers, has had the DSC system in place. Any vessel that has a VHF with DSC capability (and that has properly integrated this VHF with an onboard GPS), can sound a distress call to the US Coast Guard (and to any other vessel in the area that possesses DSC). If the owner of the vessel has properly registered the VHF with the Coast Guard, then the push-button distress call on the VHF will inform the Coast Guard not only of the vessel's name and registration information, but also the precise latitude and longitude of the vessel as indicated by the GPS. Digital Selective Calling thus serves as a coastal EPIRB system of sorts, EPIRB (Emergency Position Indicating Radio Beacon) being the satellite-based system for the open ocean. From the very start of my refitting of Oystercatcher, my Ericson 25, I knew that I wanted the boat to be DSC capable. As I have said many times, the overall goal in my refitting of this boat, was to make it suitable for coastal cruising. Having DSC capability was thus, from my perspective, mandatory. In this posting, I describe the installation of the new VHF and the infrastructure I created to support Digital Selective Calling.
As I have said in many other postings, when I purchased the boat in 2009, she was well-cared for in terms of her bottom, but in almost all other areas she was lacking. One of these was the VHF radio and the VHF antenna. The boat had an antenna at the top of the mast, but it looked like it was two or three decades old. More troubling was the fact that the coaxial cable that joined it was corroded. This, of course, I would later discover after I had purchased the boat and dropped the mast.
The picture below I took at the time of purchase. The coaxial cable, which originated at the top of the mast, terminated, of course, at the back of the VHF radio. This end of the cable, like the opposite end, was also corroded.
The VHF radio, despite its obvious old age, actually worked, but its effectiveness was questionable, especially in the area of transmitting voice, since the cable suffered from so much corrosion. The cable was also, as I would later figure out, far smaller in diameter than it should have been. One of the first things I did after I got the boat back home to Charleston was to remove this VHF and the other outdated electronic devices (that were located nearby).
As I said in the earlier postings in this series, in place of the defunct instruments that had been mounted on the cabin trunk, I installed a Garmin GPSmap 541s.
On the back of the GPSmap 541s there are three connectors. From left to right they are as follows: the wiring harness connector; the NMEA 2000 connector; and the external GPS antenna connector. I had no plans to use the antenna connector, since an antenna was unnecessary due to the cabin trunk mounting position of the GPS itself. I also had no plans to use the NMEA 2000 connector, at least at this time. If I ever wanted to add the optional Garmin GXM-51 Satellite Weather Receiver, this would be where I would plug it. This left the wiring harness connector. The GPSmap 541s is a NMEA 0183 device that is capable of reading NMEA 2000 sentences. Thus, it could perhaps be described as a bilingual device. NMEA stands for National Marine Electronics Association. This trade association establishes the standards by which marine electronic devices communicate with each other. NMEA 2000 is slowly replacing NMEA 0183. One of the benefits of the newer protocol is its simplicity in the area of wiring. In lieu multiple wires in a wiring harness, such as we see with NMEA 0183, NMEA 2000 uses but a single cable.
Since the GPSmap 541s is a NMEA 0183 device, a wiring harness, with multiple individual wires, is necessary. Below, we see the wiring harness plugged into the connector. There are two separate cables in the harness. The first contains the many different wires, each of a different color, for the NMEA 0183 system. The second contains a plug for the transducer. In this posting, the fifth in a seven-part series, I will not address the transducer. That is the subject of the six posting in this series. Nor will I address the NMEA 0183 wiring itself. That is the subject of the seventh and final posting. See those postings for those details. See also the separate posting, "Electrical Diagram, GPS, VHF, and Tiller Pilot."
You'll notice in the picture above that, next to the clump of colored NMEA 0183wires, there is a small plug. This belongs to the transducer, pictured below. At this point, before the installation of the transducer, I simply wanted to make sure that its plug fit the plug in the wiring harness of the GPS.

Satisfied with the general appearance and fit of the wiring harness, I turned my attention to the VHF. Specifically, I sought a good location for mounting it. The VHF had to be relatively close to the GPS, and it had to be relatively close to the cockpit. In the picture below, we see the mounting bracket placed between the circular area to the left, which would house the backing plate for the winch, and the two bolt holes to the right, where a deck cleat for the winch would be located.
I could not put the VHF forward of the circular backing plate for the winch, because the handrail would be located in that area. You can see one of the bolt holes for the handrail in this picture.
The fit was snug, but then again, just about everything in this boat was snug. I had just enough room to see the screen and turn the knobs. In case you're wondering, this is a Standard Horizon brand Eclipse DSC+ GX1100S. I came close to buying the more expensive Standard Horizon VHF with both DSC and a Class B AIS (Automatic Identification System). This Class B (receive-only) AIS feature would have allowed me to see and identify other vessels with Class A (transceiver-receive) AIS capability on a small screen. In other words, this small screen would serve as a radar of sorts. I figured that the day might come when I would upgrade to this (especially after the technology had improved and the price had come down, thus enabling more vessels to have AIS and thus been detected by AIS), but for now DSC capability would serve me just fine.
My wiring diagram called for a terminal block of at least 9 positions to accommodate the many wires necessary for integrating the GPS, the VHF, and also the Tiller Pilot (that I one day planned to add to the boat). In my diagram, I had drawn two separate terminal blocks. When the time came for me to do this hands-on work, however, I realized that one single block of 10 positions would fit better in the space that I had available to me. Below, we see a Blue Sea Systems 30 amp block. We also see a trim piece of mahogany and some stainless steel finish washers. Did I really need to use a mahogany trim piece for this? No. Did it make it look much better? Yes.
The cockpit sole, my worktable and epoxy-mixing station for many of the projects associated with this refit.
The trim piece installed.
Below, we see the terminal block installed. Notice the old plastic tracks for the non-existent curtains to the left. I considered reusing these tracks for new curtains that I would make. I read many an article and many a forum posting on the making of new curtains. Eventually, I decided that I did not like any of the traditional curtain ideas. I also did not like the extraordinarily expensive curtain track-slides (that were nothing more than pieces of cheap plastic) that I would have to buy. Nor did I like the approach that some had made by stringing shock-cord from one eyelet to another on either end of the portlights. That to me looked sort of raunchy, like a cheap motel. After numerous hours and numerous cans of barley and hops, my contemplations ultimately led me to do something entirely different. I decided I would trim the portlights with mahogany, and to these pieces of trim I would snap the curtain, or I should say curtains, in place. Two different types of curtains for two different purposes - one dark, for blocking light, and one translucent for admitting light, but not direct sunlight. On cloudy days, when direct sunlight was not an issue, I could opt to have no curtain at all. Under these circumstances, the portlights would still look nice, since they would be framed by that mahogany trim. For more on this project, which I carried out at this time, see my article, "Portlights, Mahogany Trim."
One of things that led me to install the mahogany trim around the portlights was my need to install the little piezo alarm that you see pictured below. This device would be wired to the GPS, and it would serve as the anchor alarm. If the boat dragged anchor outside of a specified radius around the boat, then the GPS would activate the alarm. In case you're wondering, I ordered this piezo alarm from Defender in Connecticut.
Voila. Now you see why I was led to add the trim to the portlights. Doesn't that little piezo alarm, with its mahogany trim piece look like it's supposed to be there?
Here's a view from afar. Notice that next to the piezo alarm trim piece I have added two more trim pieces. At this point I had only taped them in place to get an idea of how they would look. To me, this sequence of three trim pieces looked good, especially since it corresponded to other sequences of three elsewhere in the boat. Two examples we can see in the picture below. There are three compartments in the spice rack behind the sink (this spice rack would later have three rails on its front). There are also three mahogany trim pieces on the Spanish cedar splash shield. For more on the other sequences of three on the other side of the galley, see my article, "Electrical, Battery Charger, Part 2: Splash Shield Construction."
Here's a close up. Yes, this sequence of three trim pieces was pleasing to the eye, but there was also a practical purpose for them. Notice that the microphone for the VHF is hanging free.
I needed some place to mount the microphone bracket. The mahogany trim piece on the far left was just the right place for it.
There was just enough space on either side of the microphone to grab it and remove it from the bracket with your hand. Thus, the middle mahogany trim piece would need to remain simply a decorative item.
One final thing . . . see the piece of duct tape next to the VHF? Pay no attention to that. Shortly before I took this picture and the other pictures I have included in this posting, this tape had held a mock-up backing-plate in place. The mock-up fell, and I forgot to remove the tape.
Having installed the VHF, the terminal block, and the three mahogany trim pieces, the infrastructure was now in place for me make the connections between the VHF and the GPS that would enable the Digital Selective Calling capabilities of these devices. One final thing that I needed to do was to install the through-hull transducer. This is the subject of the sixth part of this seven-part series.

This ends this posting on the infrastructure I created for the VHF and Digital Selective Calling on Oystercatcher, my Ericson 25.

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