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Installing Radar

This article was originally published in July, 2000 on SailNet.

Which way is this weather moving? Your eyes can give you a general indication, but radar can tell you precisely where and how fast storm cells are moving.
Radar is one of those things that, once you've tried it once, you're prompted to say: 'Gee, I had no idea what I was missing!' All of a sudden you have the ability to pick out and track both moving and stationary objects in darkness, fog, and other instances of restricted visibility. And all of this from miles away. You can even see rainfall coming your way at night and have your foulies on before it hits. Basically, for the cruising sailor, radar can provide great peace of mind and when used properly it can ensure much safer boating for everyone on the water.

When we decided to move the radar dome on Serengeti from a wobbly pole on the stern rail to a position high on the mast, I had temporarily forgotten our agreement that Larry does all the work below the waterline, and I do the jobs up the mast. It soon dawned on me that this was going to mean several lengthy trips up in the bosun's chair to drill and tap the mast for the new mount. And to be honest, at this point, the only thing I knew about tapping was what I'd seen from the likes of Sammy Davis, Jr.

Nonetheless, I know now that whether you're moving an existing radar unit on the boat as we did, or installing a new one, the basic procedure remains the same. Here's an overview of the various factors that must be considered when installing a radar unit, as well as some step-by-step instructions to follow when mounting your radar dome on the mast.

All radars built for sailboats incorporate the transmitter, antenna, and part of the receiver in a protective dome called a radome. This dome protects the spinning electrical stuff inside from sheets and rigging, etc., and allows for greater mounting flexibility. In determining a mounting location for your radome, keep in mind that the length of cable provided must connect to the display/control unit. Optional lengths are available, but it's one less hassle if you plan ahead to use the cable length that's supplied.

Some sailors prefer mounting the randome on a pole secured to the transom (as shown above).
Many different mounts are available for radomes. On sailboats, you'll see them mounted on brackets on the forward side of the main or mizzen mast, on a pole at the stern, or on a special backstay mount. Each of these locations will provide satisfactory results and the mounts needed are widely available commercially. Some sailors fabricate custom radar arches that are also useful in mounting other antennas. The mast mount is the least expensive, but the most involved to install. You'll have to decide for yourself which one provides the right mix of looks and function for your boat.

On board Serengeti there's a lot happening visually at the stern rail with davits, a wind generator, and solar panels. To achieve a cleaner look, and a clear corner for fishing, we decided to move our radome from a pole on the stern to the mast. We had a mast-mounted randome on our last boat and were very happy with the performance from that location.

The textbooks tell you that when a radar is mounted rigidly, signal reflection could be lost when the boat heels. It's been our experience, however, that there is very little loss under normal sailing conditions. The majority of cruisers using radar out on the water have rigid mounts. If you're still concerned though, there are self-leveling mounts available for all mounting locations, which will ensure that the radar beam remains perfectly oriented with the horizon.

Having a display down below like this one is fine, but having one that's visible from the helm can truly aid a shorthanded crew.

The display part of a radar, historically seen only at the nav station in sailboats, can actually be positioned anywhere you choose. Waterproof models are commonly seen at the helm, at the nav station, and sometimes in both locations. Some of the newer models allow connecting two displays to one radome, thus providing an integrated dual station. Others include a chart plotter and a GPS function. Pretty soon, we figure we'll be able to reheat coffee in one of these puppies. If Larry and I were purchasing a new radar today, we'd take a serious look at the models that provide this flexibility and integration, having experienced firsthand the usefulness of a waterproof LCD display right at the helm during foggy days in Maine, and while sailing offshore at night.

On Serengeti, we inherited a Furuno radar with a non-waterproof CRT display that was already installed just above the nav station on a pivoting bracket. From this location, the monitor could easily be seen from the port side of the cockpit, as well as from down below at the nav station. This is a sensible arrangement for a non-waterproof display, so we decided to leave it in place.

After mounting your radar display, you'll need to make several electrical connections, so make sure you've chosen a location and mounting method that allows easy access to the wiring behind the unit. This will make both your present job, and troubleshooting down the road, much easier.

"You'll also need power to the unit and this means running a pair of power cables from the back of the display to your electrical panel."
The cable that will lead to the radome must be connected to the display. This is usually a single cable and plug that inserts into the back of the unit. You'll also need power to the unit and this means running a pair of power cables from the back of the display to your electrical panel. Always use a dedicated circuit breaker. The power cables running to your radar should also be fused according to the manufacturer's specifications. If it's not already included, add the recommended amperage in-line fuse on your positive power lead. You may also be asked by the manufacturer to ground the display case to your ship's ground. Other optional connections, such as a NMEA or Sea-Talk interface, are usually just simple plug-ins.

Before going up the mast, I familiarized myself with all the components involved in attaching the mount to the mast. I had the bracket, the machine screws, the drill, tap, caulking, Tef-gel, pencil, and screwdriver. I'm pretty handy with a drill already, but I didn't know anything about tapping a mast to receive machine screws. Larry gave me a quick session of Tapping 101, and before giving me a passing grade, made sure my taps were straight by making me practice on a scrap piece of aluminum. This definitely helped, since I didn't botch any of the real ones later. Riveting the mount to the mast is another option, but not as convenient if you ever want to remove your bracket in the future.

Next, I studied the method of hooking up the cable—it would come out of the mast and connect to the innards of the radome. This meant taking the top off the radome and practicing the connections that I would have to make up in the air. There's no way I wanted to have to keep making trips up that mast to troubleshoot if things didn't work when I was finished.

On most models, the connections are very simple. This Furuno unit that the authors installed required only three connections and a ground.
We measured the length of cable we had available to us from the display unit, and then laid out its new path to the mast, making sure we knew what length was left over for the run up the mast. We had chosen a spot just below our lower spreaders for the radome, but had to use a tape measure to ensure we had enough cable for this position. Our specific height, which ended up being 17 feet above the deck, was determined by our plan to store a 15-foot whisker pole vertically on a track on the forward face of the mast.

I loaded up the bosun's chair with various small tools that I would need during the installation process, leaving the larger items to be lifted up individually in a tote bag later via a line hanging down from my chair. Larry hoisted me up and, as always, complained I wasn't helping him any by climbing. Although two halyards secured me, I took an extra line, which I tied around the lower spreaders, to secure to my bosun's chair. We know of a rigger who drilled into a mast and through the internal halyard that was supporting him. Unfortunately, he fell to his death.

Once in position, we re-checked the height above deck and confirmed that our chosen spot was within reach of our cable. Larry then hoisted the bracket to me using another halyard. I positioned the bracket around the mast while Larry sighted it from off the boat to make sure it was level. I marked this spot with a pencil. Because the bracket fit tightly around the mast with the halyard holding it in place, I was able to start drilling holes immediately.

After each hole was drilled, I carefully ran a tap into the mast, threading it to receive a quarter-inch machine screw. Each screw was dry fitted as I went along to make sure nothing shifted. Somehow, things went way better than I expected.

Drilling and tapping in mid air, Sue managed to get the randome mounted and connected with very little fuss.

Next, I removed the mount, and lowered it to Larry. While he permanently bolted the radome to the mount, I drilled a much larger hole just above the mount location that would allow us to bring the radar cable up out of the mast to the radome. Large diameter drill bits can create torque and resistance that can make drilling dangerous, especially when working from a bosun's chair. We decided to use a three-quarter-inch hole saw that made the drilling process smoother and safer. This was pretty easy. The edges of the hole were a little rough, so I used the file-like handle of the tap set to remove the burrs, preventing possible chafe through the important cable it would house.

Through this hole, I dropped a long, thin line that was weighted at the bottom and waited as Larry fished it out through the hole he had previously drilled inside the boat near the base of the mast. A straightened coat hanger with a little hook bent at the tip worked great here. Larry taped the end of the cable to the line and I pulled it carefully up the mast while he fed the cable from below. Since the cable is pretty thick (about a half inch in diameter) and has large plastic connectors on the end, it took a little fiddling to get the end through my three-quarter-inch hole. Not wanting the cable to slip back down the mast, I quickly secured it to a nearby stay.

With everything in order up top, Larry hoisted the mount back up to me, only this time with the radome unit attached. We left the dome cover on, even though I would have to remove it again, because we didn't want to damage any of the delicate innards during the hoist. I guided the position of the mount and radar back on the mast and lined up the holes. This time I installed each machine screw with Tef-gel to reduce the electrolysis that can occur with a stainless screw going into an aluminum mast. All that was left to do was to attach the cable to the radome.

"I unscrewed the cable at the back of the radome and a large rubber seal immediately dropped to the deck below."
I removed the dome cover and gently lowered it to Larry. Grabbing the end of the cable, I slid on a rubber grommet to help seal the hole through the mast. Next, I unscrewed the external entry point for the cable at the back of the radome. A large rubber seal immediately dropped to the deck below and bounced around several times. "Missing something?" Larry called up as he retrieved the seal and sent it back up to me. Ignoring him, I continued to attach the cable.

Our Furuno model 1721 radar has just three very simple snap on electrical connections to make at the radome, but I had to make sure that I heard the little plastic locks snap into place. Each plug could only go in one place and in one direction, so there was no danger of connecting them incorrectly. There was also a ground wire that had to be secured under one of the screws that locked the cable into place with a small metal gate. Happily, the connection process only took a couple of minutes, and I'm by no means a Radio Shack geek. I re-acknowledged Larry's existence and called for the dome cover to be sent back up. The excess cable was pushed back down the mast, and the rubber grommet secured with the help of some silicone caulking. I was done!

"Sue, I'm proud of you. I have to admit I wasn't sure you were going to be able to do this job," Larry admitted to me as soon as I had two feet back on the deck.

"A deal's a deal, buddy!" I responded, not letting on that I had kind of felt the same way. "Now, doesn't our bottom need cleaning?"

Suggested Reading:

Navigating with Radar by Jim Sexton

The Wonders of Radar by Liza Copeland

Reflections on Cruising Instruments by Tom Wood

SailNet Store Section: Radars

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