Stern Mounted Radar Installation

by Jon Vez
Thursday, January 19 2006 @ 03:15 PM EST

Stern Mount Radar installation -Catalina 320

Previously published in Mainsheet, Spring 2003 See Photos in Photo Gallery

Following is a description for the installation of a stern mounted Radar on the 320. I have included a list of what is needed to complete the job, along with some pictures. I will try to provide estimates of the time each step took. If you prepare everything you need in advance, this project can be completed in a day with 2 people. Like many projects, what seemed like a straightforward winter project turned into something of a challenge due to the need to alter some of the standard off the shelf parts for our boats. But if you follow these steps, it should be a straightforward project.

Like most of us, Radar was always high on my wish list, but both price and the uncertainty of the installation kept it fairly low on my priority list. I also debated whether to go with a mast installation, or a stern mount installation. As both have pros & cons, I couldn't decide which way to go.

However, boatyard serendipity came into play last fall and made the decision for me. A racer/cruiser of mid 80's vintage would become my winter-on-the-hard neighbor and the owner decided to become more racer than cruiser, and proceeded to rid his boat of all things cruiser-including his Furuno 1621 Radar setup. The price was right, all of the (stern mount) installation gear was part of the deal so I couldn't refuse! The stern mount decision was made for me, and I reasoned it would also help somewhat with the infamous Port List (it didn't), and I wouldn't have to go searching for various installation parts (I did). So here's a step by step description of what I did, and more importantly what to avoid.

Parts & Tools needed:

1 Edson Stern mounting pole (standard 2 1/8" Diameter, 90" height, brushed aluminum (white enamel also available)
1 Pivoting mounting Bracket (Edson, Fold Down adapter, Part#990-23; Pivot Bracket w/Backing plate, Part #992-35)
2 Rail Mount Bracket kit: Two sets for both rails (Edson, Part #988-23-100)
4 Thru Bolts for Mounting Bracket
1 Cableclam (use medium size for standard small Radar)
2 spacing blocks for Rail mounts cut to size
Cable Ties
Display Mounting Bracket (West Marine, pg. 151) for Display unit (if mounting at Nav station)
Drill, hole cutter, & Caulking/Bedding compound

The parts above are all you should need. However the first thing I learned was that the standard Edson mounting bracket and rail kit does not properly fit the 320's stern due to the distance between the transom and the stern rail (the rail mounting brackets are designed for a maximum of 2" from pole to stern rail). In deciding where to put the pole, I determined the port side was a must (see above) and I did not want to mount it on the molded-in step on the swim platform so that I wouldn't clutter up this space. As it turns out, the distance to the stern rails used for mounting would have rendered this a bigger problem than mounting it flush on the transom. The greater the distance from the rail, the more creative (and expensive) the solution. You will end up taking up a lot of space back there if you try to mount it on a horizontal surface. One other advantage of this setup is that the radome, pole, AND cable are removable for future servicing, storage, etc.
Mount the pole-mounting bracket on the stern so that the backing plate is even with the top inner lip of the stern lazarette. This will give you enough room to get at the nuts for the backing plate bolts with plenty of clearance. Finally align the plate so that it bisects the stern rail section. This position gives a good height for the Radome and will be out of the way of everything, including the flag mount and the stern pushpit seats. It will also allow you to get to the Radome without needing a ladder. This position also does not use up any valuable interior storage locker space. I am not sure if Edson supplies the thru bolts for the mounting bracket, but they are standard stainless bolts. As far as the cable from the radome, you have two choices. You can either run it through the pole as I did, which requires drilling an exit hole in the pole a little larger than the diameter of the cable end fitting, (file the hole smooth and add chafing tape where the cable exits), or run the cable down the outside of the pole and tape it every 18". Plan on about 90 minutes for this portion of the project. Finally, use a bedding compound for the bolt heads and holes for water-tightness. Edson provides rubber nitrile pads for both sides of the mounting bracket, but I added the sealant as an extra measure.
Before installing the pole on the plate, you will find that although the plate swivels, it is not designed for being placed on a vertical plane as this installation requires. It is designed for a sloping or horizontal surface, but of course, not vertical! Although Edson provides a horizontal bracket for mounting vertical, the problem here again is that it moves the pole further out from the stern rail. The solution is actually quite simple, and only takes about 15 minutes. Take a round metal file and file down the aluminum cup that holds the pole itself. You will see a protrusion on the stainless steel mounting bracket and a corresponding dimple in the cup (fold down adapter that fits on the mounting end of the pole). You need to carve out just enough of the aluminum to allow the pole to stand in a perfectly vertical position to the stern. It's important to remember that by filing this dimple, you will be removing the white baked on enamel from the aluminum, thus exposing the bare aluminum to the stainless mounting bracket-not a good thing galvanically. You can either place a piece of thin rubber between the dissimilar metals, re-coat the aluminum, or cut enough away so that there is a gap.
Once you have the pole in place, attach it with the stern rail mounting brackets. Here you will find that the brackets are designed to have the pole mounted flush to the stern rails, or a maximum of 2" clearance. Because the stern rail is mounted slightly inboard of the transom, you will have a gap of a little over 3 inches. This is where you will use the spacers to fit in between the rail mount plates and the pole itself. I made mine out of teak blocks, but Polyboard would work fine. Once you've secured the pole, make sure the alignment is true, and then tighten everything down. This should take about 90 minutes, including cutting the spacer blocks
Drill a hole in the transom next to the mounting bracket to accept your radar cable. You should remember to drill the hole the size of the cable end fitting so that you do not have to cut and resplice the fitting that will attach to your display. I used a Cableclam (available at West, BoatUS, Defender, etc, ...) to create a watertight through hull fitting for the rather large cable. Again, make sure to caulk the screws, as well as the surrounding hole inside to ensure no water seeps into the Fiberglass. Follow the instructions on the Cableclam, which is fairly straightforward, but make sure you heed their advice to keep the rubber stopper wet when you drill this for your cable diameter. The measuring is the most time consuming and critical part of this job! This should take no more than 45 minutes to an hour.

You're done with the exterior part of the installation! Now on to the interior.

Another big decision where to mount the display. I chose the Nav station because I wanted my GPS chartplotter at the helm, since I use it all the time. One other consideration is the difficulty of feeding the electrical cable through the already filled Pedestal tubes, which would require drilling a hole in the tubing where you run the risk of hitting other instrument wiring.

Take the radar cable and bring it across the inside of the transom to the port side stern lazarette and around the refrigerator compressor. It's important to run the cable loosely and do not tie it down until you are finished with the installation. Next feed the cable in through the large port lazarette, and finally into the cabin through where the Battery Charger cables go into the boat. You will need to fish the line out through the aft most galley storage cabinet (the one against the hull, not over the refer). It is really a two-person job and will take some patience, but no drilling is required. Once you have brought the cable through this cabinet, you will do the same for the other two. If you have the microwave installation, you will need to remove the two bracket screws that hold the microwave in place and slide the microwave slightly forward to get the cable to pass through this cabinet. You should use the existing wire chasers at the top of the cabinets. It will be out of sight, and there is plenty of room to accommodate it. Finally, the third cabinet requires that you remove the two top trim pieces inside the cabinet, as well as the veneer panel that the AC outlet is attached to. I found I had to remove the outlet's faceplate and the two bottom screws holding the outlet in place in order to move this panel. Once the panel is removed, push/pull the cable through the chaser in the top back corner of the cabinet. You will see that this is where all of the other cables are coming through (including AC wires, so be sure to disconnect shore power and/or kill the AC circuit breaker from the STERN BREAKER in the port locker). This is the toughest area to feed the cable, but you are almost done! Once you have fished the cable through this last cabinet, pull out a couple of feet worth (but not too much) from the exit point, which will be the top corner of the shelf area above the Electric panel. This takes about 2 hours depending on how good you are at fishing the cable through tight spots.
Now you are ready to do the electrical connection. Take the electrical cables that came with your unit and fish the ends that WILL ATTACH TO YOUR DISPLAY UNIT from the inside of the Electrical panel and up through the back of the galley cabinet opening you just pushed the radar cable from and back out of the same hole that the radar cable just terminated. This is a clean way to run your electrical cables without unnecessary drilling and it uses existing cable conduits.
Now that you have the cables where you need them, the next step is to mount your display. I chose to mount mine in a place that is out of the way when not in use, yet is adjustable for viewing from anywhere in the cabin, and also from the cockpit from under the Dodger. Place the mounting bracket (see part number above) as high as possible on the bulkhead that separates the galley from the salon. You will need to simply shift the mounting arm "upside down" by switching the adjustment knob so that you can position the mount as high as possible. Attach the positive to an available circuit switch, add the negative/ground to the bus bar and you are done!