Making your own radar mast.

Radar was the next item on the list in the continuing process of getting Andiamo, our Wauquiez Pretorien 35, outfitted for extended voyaging. I talked to a lot of folks and decided to install the radar on its own dedicated mast, mounted on the stern. I also added a separate mast, mirroring the location of the radar mast, for a future wind generator.

The two masts were engineered to cantilever out of the deck, so there’s no bracing to get in the way. One of the advantages of having a separate mast is that I can move our antenna farm (GPS, 2-meter and second VHF) up from the pushpit, out of harm’s way. Another advantage is that we can use the masts as derricks by adding booms, and we can use the booms as davits for carrying the dink during short hops in protected waters. We were on a very tight outfitting budget, so the challenge was to figure out how to do a professional-looking installation with amateur tools and skills. The first thing was to find components for fabricating and installing the masts.

There was only a small area of deck behind the coaming where the mast would fit and clear the pushpit. I needed to be able to drill a 2-1/2-inch-minimum-diameter hole for each mast and be able to finish it both attractively and with a good degree of weather-tightness. I found a manufacturer of stock stainless-steel pipe and tubing flanges that I could adapt to my needs. I purchased two and had a local machine shop trim the flanges and drill the holes. I later tapped the side holes for the setscrews. I chose a pipe flange that was larger than my tubing size so there would be room for finely adjusting the mast to be true and plumb. Selecting oversized flanges also solved the problem of compensating for the deck’s camber. The flanges allow for tolerance in the installation. The actual opening in the flange is 2 7/8 inches. When the fabrication was finished, I polished the stainless to a near mirror finish to reduce its tendency to corrode. The flanges were only available in type 304, so I’ll make sure they stay well waxed.

Next came the masts themselves. I found a local vendor of stainless-steel pipe and tubing. A 20-foot piece of 316L tubing, 2-1/2-inch-diameter by 0.12 wall thickness, in a bright annealed finish cost $260. That was only $130 per mast and fit our budget nicely. The wall thickness is enough to drill and tap, or the components could simply through-bolt onto the mast.

Next came the design and detailing of the radar base and the boom/davit design. I was able to purchase remnant pieces of 1/2-inch-thick, 16-by-20-inch aluminum plate, 4-by-4-by-1/8-inch aluminum angle for the radar platform and some 2-by-2-by-1/8-inch aluminum tubing, and some 1-1/4-by-2-1/2-by-1/8-inch aluminum tubing for the booms. I fabricated all of the aluminum and had it powder painted. The machine shop did a “marine” finish, with the cost of about $140 for 11 pieces. One thing to remember is to overdrill the holes by 0.05 to allow for the thickness of the powder paint. The gooseneck toggle was made out of high-density polyethylene (HDPE), and the gooseneck is simply a toggle and T-bolt.


The flanges were installed through teak block bases that were shaped to fit the stern-deck coaming area. The wood hull-deck covering trim was cut out to avoid any standing water and to provide a scupper to allow the water to flow overboard. The blocking was installed first, bedded in 3M 4200 adhesive and anchored in place with a couple of 2-inch No. 10 flathead wood screws. The flange was then located on the block and also bedded with 4200. Four 3/8-inch holes were drilled, and the flanges were secured with washers under the deck. Then a 2-3/4-inch hole was drilled through the wood and fiberglass deck.

A cardboard tube for vertical reference and a helper on deck helped locate the place for the 2x mahogany wood anchor blocking inside the hull. Gear and people were moved around to get the level to read properly. The block was centered under the hole and the location marked. I planed and sanded the block for a snug fit to the inside curvature of the hull. Here’s a trick to remember: Apply chalk to the area of the hull where you want to fit the block. Press the block to the hull and just keep sanding away the wood where the chalk appears. When it’s mostly chalk, it’s fitted. After sanding the hull with 36-grit paper and cleaning it with acetone, I mixed up a thick batch of epoxy with microballoon filler and secured it in place to dry with a previously fitted piece of 2×4 to use as a wedge. Before the epoxy set, I pulled the wedge and covered the block with two layers of 6-ounce fiberglass cloth both ways.

The bottom of the mast is anchored to the hull using a couple of pieces of aluminum angles that are lag-bolted into the block on both sides of the pole with lag bolts 1 1/2 inches long and 3/8 of an inch in diameter. The angle-tube-angle assembly is through-bolted with a 5/16-inch bolt. All connections between stainless and aluminum are isolated with either nylon bushings and washers or an antiseize coating for corrosion protection.

Setscrews on the flanges were used to finely true up the mast and to secure it temporarily. I made a bunch of various-sized teak “mast wedges” and pounded them into place just as one would do with mast partners. The wedges were all cut off right at the top of the flange, and the masts were fixed in place. The flange was then sealed with mast boot tape and covered with a Sunbrella fabric mast boot to match the mast’s boot.

The radar platform is assembled out of aluminum pieces that are through-bolted on the mast. The bolts do double duty, as they also secure stainless strap eyes I installed just because we will be in typhoon country in a year or two, and I may want to add some extra, temporary bracing to the masts. Again, I took extreme care to make sure that all the dissimilar metals are isolated from one another to prevent corrosion. The stern light was relocated to the inboard antenna arm to provide better visibility.

The booms are designed to be removed easily for stowage below. I have a 4-to-1 fall from the boom, and I chose double blocks (instead of fiddle blocks), so I could reeve them for two-blocking and am able to raise gear as high as possible. I also installed Harken hexratchet blocks to make lifting easy. I sewed a bag with two pockets to hold the booms separately and to minimize the tendency of the lines to tangle together. The booms can also be stored vertically against the masts when appropriate. The only lines that stay on the masts are the boom-end lifts.

John and Lisa Caruso recently departed Seattle on a planned 10-year circumnavigation.

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By Ocean Navigator