How to Install a Boat Radar Antenna (Radome or Open Array)

BoatUS explains that the main limit on radar range is the curve of the Earth, so height helps, but less than you'd think. Its example: on a 35-foot cruiser with a hardtop about 10 feet off the water, raising the dome another 10 feet only added roughly a mile of range on a boat-size target. The first goal is simply to get the antenna above everyone's head. Sport Fishing Magazine quotes Garmin noting that a radar only 15 feet off the water won't reach its full range, but for collision avoidance, which is most people's main use, a good clear spot matters more than maximum height.

Pick a spot where the beam passes over the heads of anyone at the helm, on the flybridge or on deck. Practical Sailor's advice is to avoid any installation that puts crew directly in line with the radar within a few meters, and notes a high pole or backstay mount well clear of heads is not considered a measurable risk. On a hardtop where people sit on the roof or a flybridge where heads come close, raise the antenna on a riser or move it.

Stand at the planned spot and look around 360 degrees. Masts, stacks, outriggers, antennas, lights and towers in the beam cast shadows or create false echoes. Also keep the antenna away from the compass, and place GPS and VHF antennas above or below the radar's beam rather than in it (your radar's instructions give the distances). BoatUS suggests mounting a post-mounted radome on the starboard side when you can't avoid some shadowing, since boats approaching from starboard usually have the right of way.

The radar's beam should be roughly level with the horizon when the boat is underway. BoatUS notes that most fast powerboats run slightly bow-up, which can be corrected with a wedge under the dome or array (some boats have this angle built into the mount). Sailboats and displacement boats run nearly flat. Sailors who use radar while heeled can consider a gimbaled or adjustable mount; Practical Sailor notes that typical radar beams start losing targets at around 15 degrees of heel.

BoatUS points out the trade-off: a mast mount gives more range, but a lower mount is safer from halyards and sails and sees targets closer to the boat. Practical Sailor's mount reviews note that foresails flogging against a mast-mounted dome are a real threat, so a guard is a good idea, and that a stern pole needs proper support from the stern pulpit or rails. A mast-mounted radar must come off when the mast is unstepped. If you choose a gimbaled mount, read step 9 about cable flexing.

The antenna plus mount puts weight and wind load high up, and an open array adds torque as it spins. Check that the hardtop, arch, T-top or pole is solid, with no cracks, loose welds or flexing (see the tower hardware guide). For hardtops, find out whether there's a reinforced area for electronics; ask the builder. Never mount an open array on a structure that wasn't designed for it.

Use the antenna's template to mark the bolt holes, check what's under each one, and drill straight. Seal any cored hardtop or deck holes (drill oversize, fill with epoxy, redrill; see the through-bolting guide). Bed the mount with the recommended sealant and through-bolt it with stainless hardware and a backing plate underneath to spread the load. Tighten to the method or torque in the radar's instructions, evenly and without crushing the laminate. On a radome, Boating Magazine notes the breather hole at the bottom of the dome must not be blocked.

Plan where the cable will come through the hardtop, arch leg, mast or deck, and use a proper watertight gland or clam-style fitting rather than a hole and a blob of sealant. Boating Magazine's install used one on the hardtop. Leave a drip loop so water runs off before it reaches the fitting.

BoatUS is clear on two rules: never cut the plug off a radar cable to make it fit through a hole (the shielding and the connector won't be the same again), and don't strain the cable when pulling it through tubes or chases. Damaged shielding lets salt water in to eat the cable from inside. Boating Magazine suggests taping a pull line to the cable's outer jacket and taping the connector flat to the line so it can't snag or bend back. Support the cable with cushioned clamps along its run, keep it away from VHF and other antenna cables where you can, and coil any extra neatly instead of cutting it. On a gimbaled mount, Practical Sailor reports cables breaking from constant flexing; leave a gentle loop and lock the gimbal when the radar isn't in use.

Connect the cable to the display or network as the radar's instructions show (often Ethernet for newer units). Run power from a fused or breaker-protected circuit sized per the instructions, with tinned marine wire. Ground or drain wires go where the instructions say. If your boat's panel doesn't have a spare breaker or you're unsure about the network setup, this is a good point to call an electronics installer.

With everyone clear of the antenna, power up and follow the setup steps: antenna height, heading (bearing) alignment, and tuning. Check the image against known targets: a buoy or point straight ahead should show straight ahead. The radar care guide covers bearing alignment and tuning in more detail. Expect a blind ring close to the boat; that's normal.

After a few outings, check the bolts, look for any water at the pass-through and under the hardtop, and confirm nothing has loosened or chafed. Note the date in BoatMend and add the radar to your yearly check (see the radar care guide).

Then practice with it on clear days, when you can compare the screen with what you see. Lenny Rudow's BoatUS article on learning radar warns that small fiberglass boats may show up only at close range or not at all, that heavy rain can blank out much of the picture, and that steering by radar alone takes practice because the screen updates more slowly than your eyes and you lose the horizon. Don't save your first real radar run for fog.