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Installing a radar set on an older vessel

Jan 1, 2003

As every serious mariner knows, radar is an invaluable tool for both coastal navigation and for collision avoidance. Even after years of operating in the Maine fog out of Gilkey's Harbor on Isleboro Island in Maine's Penobscot Bay, we still hadn't equipped our Tartan 34 with a radar unit.

Recently, I remedied that situation by installing a radar aboard our boat. After deciding on the model of radar set to use (I chose a Raytheon unit), the next question was where to place the antenna unit. After considerable thought, I picked a radar post on the stern as my location of choice.

There are several reasons I chose an aft post mount:

1. We have a sloop, not a ketch, so mounting the radar on a ketch mizzenmast is out of the question. I would consider a mizzenmast mount on a ketch, however.

2. To avoid adding weight aloft. The radar weighs 12 pounds, plus the bracket, and 12 pounds 40 feet above the deck will have a noticeable effect on boat tenderness. Weight at the ends of the boat will also affect performance, but not as much as it would high up on the mast.

3. Since I store the boat in a covered shed when we are in Maine, it means removing the mast. Removing the mast with the radar attached means breaking the electrical connections between the mast and the boat.

4. I didn't like the idea of the headsail dragging across the radar dome on the front of the mast every time we tacked.

5. The Edson radar post can accept a bracket for other electronics; this means I can create a mini antenna farm on the post.

6. A post mount means there are no electrical connections exposed to weather, and a single 49-foot run of cable provided with the set will get from the radome to the nav station display.

7. If I need to service the radome I can hold on to the backstay and just reach the radome by standing on the stern rail.

It was not practical to mount the radar display for easy viewing by the helmsman, so I mounted the display on a teak shelf completely out of the weather at standing eye level over the chart table. We could observe the display quickly and give directions to the helmsman without having to sit. The display is at least visible from the helm. To clearly observe small targets like buoys, the display should be hooded, particularly during the day.

Now that the decision was made to mount the radome on an aft mast, the problem was to locate it. Because the boat has a slight list to port and the loran antenna was located to port, the radar mast was located to starboard just outside the stern rail. The 49-foot radar cable supplied with the unit would be long enough to reach the display below. An Edson 14-foot aluminum mast, fiberglass sleeve tube and radar platform and antenna bracket were purchased. The most difficult part of the installation was locating and securing the mast. The radar mast must be vertical, meaning the mast must be perpendicular to the water when the boat is on an even keel. With the boat at 0° of heel (as seen on the angle-of-heel gauge) a long carpenter's level was stood on end where I wanted the mast to pass through the deck. A 3-inch circle was marked on the deck where the mast sleeve should pass through the deck. I was careful not to come up under the stern rail but close enough to get added mast support from the stern rail.

I planned to support the mast at three places: hull, deck, and stern rail. Each support was about 24 inches apart; the deck was 24 inches above the hull, and the stern rail was about 24 inches above the deck.

I emptied and padded the 16-inch-square lazarette and partially crawled inside. Very carefully I measured on the underside of the deck where the sleeve was to pass through the deck and used a level again to pencil-mark the location of the mast sleeve on the hull and transom. Fortunately, I could come through the deck at the desired point and butt up against the inside of the hull and not the inside of the transom. I would hate to locate the fiberglass sleeve against a vertical transom. Knowing approximately where the mast was to rest against the hull, I designed a shoe to accept the fiberglass mast sleeve. The full weight of the aluminum mast with radar on top should not set against the fiberglass hull without a shoe to carry the load.

The shoe was made from a piece of 10-inch-square, -inch-thick marine ply wood. Some shaping of the shoe was needed to avoid the vertical transom and to fit the curvature of the hull. With the shoe shaped to fit, it was temporarily held in place using duct tape; I waited for the boat to stop moving and re-leveled and re-measured one more time. I drilled a pilot hole at the center of the 3-inch mast sleeve circle on deck and dropped a small plumb bob through the hole to confirm the center of the circle on the shoe taped to the hull below. Then I used a 3-inch hole saw and cut the mast sleeve hole in the deck.

The 48-inch Edson mast sleeve was set in place with about 24 inches protruding above the deck. The sleeve butt where it meets the shoe was marked with an carpenter's angle gauge and cut with a hacksaw to fit as snugly as possible against the hull shoe. I also made up and glassed four plywood angle brackets to add support between the fiberglass sleeve and the shoe.

Using the same angle as the sleeve, I cut one end of the aluminum mast. I wanted the radar electrical cables to exit the sleeve and mast relatively close up under the deck to keep the cables out of the way. Carefully marking the desired point where radar cables will exit the mast and sleeve, I drilled a -inch hole through both sleeve and aluminum mast. A -inch hole was also drilled below the cable exit hole through both the sleeve and mast to accept a -inch stainless steel bolt necessary to hold the mast in place.

With the sleeve and mast cut to butt against the shoe, the four angle pieces were placed around the sleeve circle drawn on the shoe, glassed to the shoe, and allowed to cure. The sleeve was duct-taped to the shoe and the mast gently lowered into the sleeve with cable and bolt holes lined up. With the mast now sticking 12 feet into the air, I walked up and down the dock to check on mast vertical alignment. I even got a second opinion. The shoe needed to be moved ever so slightly. I went on board and carefully untaped and moved the shoe and again walked the dock until I was satisfied the boat was on an even keel and the mast was vertical.

When I was satisfied that the mast was vertical, I re-marked the shoe against the hull and re-marked the butt of the sleeve on the shoe.

I removed the mast and sleeve from the boat and used West System epoxy to attach the shoe to the hull using lengths of fiberglass tape. I was careful to be sure there was plenty of resin under the shoe and at the point where the butt of the aluminum mast rested.

Early on the second day, I cut the sleeve so it protruded inch above the deck. Then I poked the sleeve through the deck and used epoxy to cement the sleeve to the shoe and the sleeve to the top and underside of deck, using lengths of fiberglass tape. I was careful that the sleeve was rotated properly so that the bottom angle cut rested against the shoe.

The radome and Edson radar platform were mated using four -inch stainless steel bolts. With the platform and radome temporarily on the top of the mast and aligned by eye fore-and-aft, a U-shaped cable channel was marked at the back of the mast to allow the radar cable to exit the mast and connect to the radome. The GPS cable hole was also marked. I had to remove the radome and mast to cut the cable holes. After getting the holes located, the radar mast was placed back in the sleeve and messenger wires were dropped from the cable holes at the top of the mast and located and pulled through the holes in the sleeve and mast under the deck. By pulling the messenger lines, the radar and GPS antenna cables were run up through the mast. Both cables were then tied off to prevent them from falling back down inside the mast.

The mast was bolted through the sleeve belowdecks and then secured. After I located the radome and GPS antenna at the top of the mast, I connected the wires while standing on the stern rail. To make sure water didn't work its way in, both cable holes were sealed with clear sealer. I made up and lashed a two-inch wooden teak block between the stern rail and the radar mast for added support.

If possible, the radar cable should not be cut; any excess should be coiled below. The display end was connected, the GPS NMEA 0183 output wires were connected, and power wires were run to a dedicated circuit breaker.

After the set is working as designed, practice is the only way to become familiar with radar. A radar trainer will help, but differentiating between targets takes practice because the radar display will not necessarily look like the chart. I bought the Radar Trainer software from Starpath Navigation and practiced plotting targets and their closest point of approach (CPA). Practice during good visibility will build confidence to trust the radar during restricted visibility when you need it most.

Dick de Grasse has made several Atlantic crossings aboard his Tartan 34 Endeavor. He wrote about replacing the engine on Endeavor in Issue No. 70.


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