Recreational Radar Care: Radome and Open-Array Cleaning, Mounts, Cables and Alignment

Put the radar in standby, then turn it off at the display. Switch off the radar's breaker or fuse at the panel and put a piece of tape with "radar work, do not switch on" over it. On boats with several helm stations, make sure no other display can wake the radar. Only then go near the antenna.

Before climbing up, look at the radar with a phone camera on zoom from the deck or dock. Note anything unusual:

• Cracks, chips or crazing in the radome shell or open-array cover
• Bird droppings, soot, salt crust or spider webs
• A tilted or loose mount, missing bolts, or rust streaks running down from bolt heads
• A cable that hangs loose, rubs on rigging or has cracked insulation

A dirty radome does not stop the radar from transmitting, but salt, soot and grime weaken the faint echoes coming back, so small targets such as a crab-pot float or a small boat can fade from the screen. To clean it:

• Wash with mild boat soap and a soft sponge, rinse with fresh water and dry with a soft towel.
• Do not use solvents, abrasive pads, polishing compound or a pressure washer, and do not sandblast it.
• Never paint a radome. Paint, especially paint with metal in it, can block the signal. A light coat of wax is fine for looks but does nothing for performance.

The front face of an open array lets the signal through, so treat it gently. Wipe a flat array face lightly with a damp cloth and fresh water. If your model has an open slotted aluminum element, remove dust and spider webs with a soft brush or low-pressure air rather than scrubbing. Rinse salt off the pedestal and wipe it dry. Again, no solvents, no paint, no pressure washer.

Try to rock the radome or pedestal by hand. It should not move at all. Look for:

• Loose or missing bolts, and rust or white powder where stainless bolts meet an aluminum mast bracket or arch
• Cracks in the mounting plate, bracket welds or the hardtop around the base
• A mount that has drifted out of level, which can hurt performance in waves

Snug loose fasteners to the maker's spec. Replace corroded bolts one at a time with new stainless hardware so the antenna is never sitting loose. If the bracket itself is cracked or the hardtop is soft around the base, stop and have it repaired before you run the radar again. A falling radar is heavy and dangerous.

Follow the radar cable from the antenna to the display or network switch with a flashlight. Look for chafe where it passes over the mast step, through deck glands or around sharp edges, UV-cracked jacket on exposed runs, and kinks. On masts, the cable should be secured so it cannot slap inside the mast or rub on halyards. Replace UV-damaged cable ties with UV-resistant ones and add a clamp where the cable sags.

If a previous owner or installer cut the plug off to fish the cable through a smaller hole and spliced it back, note it. BoatUS warns never to cut the plug off a radar cable, because damaging the cable's shielding reduces the radar's performance. A spliced radar cable can cause weak pictures and dropouts; have it replaced with a proper cable from the maker.

With power still off, unplug the connectors you can reach (at the pedestal, at any deck plug and behind the display). Look for green or white corrosion, bent or pushed-in pins, cracked collars and water inside. Clean light corrosion with electrical contact cleaner and let it dry fully. Use dielectric grease only if your radar maker allows it. Reconnect by hand and make sure each collar is fully seated. If you find pins that are badly corroded or a deck plug full of water, plan to replace the connector or cable section; a weak connection here causes dropouts and error messages.

Radars draw a burst of current when they start transmitting. With the radar powered on and in standby (stay well away from the antenna), measure supply voltage where it enters the radar or at its power cable, if your setup allows a safe measurement point. Then switch to transmit from the helm and watch the reading. A big drop points to a tired battery, an undersized or long supply wire, or a corroded connection or fuse holder. Low voltage can cause the radar to reset or refuse to transmit.

Remove your tag, switch on the breaker and turn on the radar. Before you press transmit, make sure nobody is up the mast, on the hardtop or standing level with the antenna. Watch for:

• Normal warm-up and no error messages
• A smooth, quiet rotation with no grinding or clicking
• A clear picture of nearby shoreline, buoys and boats

Know what "normal" looks like before you blame the hardware. BoatUS explains that traditional pulse (magnetron) radars have a blind ring right around the boat, often 100 feet or more, where they can't show anything; newer solid-state radars see much closer in. Small fiberglass boats can return weak echoes that come and go, and heavy rain can hide what's behind it. None of that means the radar is broken.

If the display shows a "no antenna," communication or motor error, go back to the cable and connector checks. If the error stays, call the maker's support or a marine electronics dealer.

Bearing alignment makes sure a target the radar shows dead ahead really is dead ahead. Raymarine's procedure, in short: point the bow at a fixed object such as a marker or a point of land a quarter mile to two miles away, turn the gain down so the target looks as small as possible, and see whether it sits right under the heading line on the screen. If it does not, adjust the bearing alignment setting (in the installation menu on many Raymarine displays) until it does.

Garmin calls the same setting the front-of-boat offset. Its manual describes taking a compass bearing on a fixed target, comparing it with the bearing the radar shows, and adjusting the offset if they differ by more than about one degree. Other makers have a similar setting in the installation menu. Do this check in calm water at low speed, with someone else steering and keeping a proper lookout.

For radar overlay on the chart and for target tracking (MARPA), the radar needs good heading data from a compass or heading sensor. If the radar picture looks rotated against the chart overlay even though bearing alignment is right, the heading sensor may need its own calibration. Follow your heading sensor's instructions.

Most modern radars tune themselves. If the picture looks weak, try the automatic gain, sea clutter and rain settings first, then compare with a known target. Many displays also have a "restore radar defaults" option. Write down any installation settings before you reset them.

• Rinse salt off the antenna and pedestal and let it dry before covering the boat.
• Turn the radar off at its breaker for the season so a stray switch cannot start it.
• If the mast is coming down, label and cap the radar connector at the mast step before it is unplugged, and coil the cable so it cannot be crushed or stepped on.
• Shrink-wrap and winter covers should not press on a radome or bend an open array. Ask the yard to frame around it.
• In spring, check connectors again before the first start.