Marine Radar Australia

Radar is the only recreational navigation technology that independently observes the physical world.

Everything else on the boat is, in some sense, reading a document. GPS tells you where the receiver is. Charts tell you what someone surveyed, possibly decades ago. AIS tells you what cooperating vessels have chosen to broadcast. Radar transmits energy into the environment and measures what comes back — it is the only sensor that finds out for itself.

For offshore cruising, night passages, poor visibility and busy coastal traffic, that independence is exceptionally valuable. It is also the sensor most often fitted and least often learned.

#What radar can detect

Depending on target and conditions:

• ships, and their wake at close range
• yachts, though weakly and intermittently
• fishing vessels, including ones with no AIS
• buoys and navigation marks
• headlands, islands and breakwaters
• rain cells and squalls
• birds, occasionally, over bait
• some floating objects, if they present a reflective surface

#What radar can miss

And this list is the one that matters:

• kayaks and paddle craft
• small timber boats
• low fibreglass dinghies
• floating debris and containers riding low
• partially submerged objects
• anything in the sea clutter close aboard, if the clutter control is set too hard

A clear radar screen does not prove the water ahead is empty. It proves that nothing within range returned enough energy for the receiver, at its current settings, to distinguish from noise. Those are very different statements, and the difference is why the collision regulations require a lookout by sight and hearing as well as by all available means.

#How it works

The antenna transmits radio energy in a narrow beam and rotates.

A target reflects some fraction of that energy back. Range is calculated from the round-trip travel time; bearing comes from where the antenna was pointing when the echo returned. Modern processing turns thousands of these returns per sweep into a target picture, suppresses noise, and — with Doppler — measures whether the target is closing.

Two consequences follow from the geometry. First, the beam travels in a straight line, so anything below the radar horizon is invisible. Second, bearing accuracy is limited by beam width, which is why two targets close together in bearing can merge.

#Maximum range is overrated

A radar advertised at 48 NM will not detect every boat at 48 NM. It will not reliably detect a yacht at 12.

Actual detection depends on:

• antenna height — the dominant factor, because it sets the horizon
• target height
• target reflectivity — a steel ship and a fibreglass dinghy are not comparable
• sea state, which raises the clutter floor
• rain, which attenuates and obscures
• beam width
• processing quality

For cruising yachts, the most valuable range is often from a fraction of a mile out to around 12 NM. That is where collision and pilotage decisions actually happen. A radar optimised for close-range clarity and fast refresh is worth more than one with a larger number on the box — the argument developed in best marine radar.

#Solid state versus magnetron

#Magnetron

Traditional high-peak-power radar using a magnetron valve.

Advantages: proven, and good long-range capability for the money.

Disadvantages: warm-up time before it transmits, higher power consumption, and the magnetron ages and eventually needs replacing.

#Solid state

Semiconductor transmitters using Sonar 2026: What the Difference Buys">pulse compression.

Advantages: near-instant startup, lower power draw, excellent close-range performance, Doppler capability, and nothing to replace as it ages.

For most new cruising-yacht installations, solid state is the logical default. The close-range performance and the low power draw both matter more on a sailing yacht than long-range capability does — power because the autopilot is already competing for it.

#Doppler

Doppler processing examines the frequency shift caused by relative motion, and manufacturers use it to colour approaching and receding targets automatically.

• VelocityTrack — Navico (Simrad, B&G)
• MotionScope — Garmin
• Raymarine Doppler
• Target Analyzer — Furuno

This is the largest single reduction in interpretation workload available to a recreational operator. At 0300 in a squall, having the closing targets already coloured is worth a great deal more than the specification sheet suggests.

It does not replace COLREG knowledge. Doppler tells you which target is closing; the regulations tell you who must do what about it. See collision avoidance.

#Radome versus open array

#Radome

An enclosed antenna in a dome.

Advantages: compact, low windage, lower weight, protected from damage, simple to mount — all of which make it the correct choice for essentially every sailing yacht.

#Open array

An exposed rotating bar antenna.

Advantages: narrower beam, stronger angular target separation, better long-range performance, usually faster rotation.

Best suited to larger motor yachts and sportfishers, where the mounting structure and windage tolerance exist. The full comparison is in radome versus open array.

#Beam width

Narrower horizontal beam width helps separate two targets at similar range but different bearings.

This is the main physical reason large open arrays retain an advantage, and it is pure aperture: a longer antenna produces a narrower beam. It matters most when the question is "is there a gap between those two ships?" rather than "is there traffic?"

#Rotation speed

A 60 RPM radar completes roughly one sweep per second.

Faster refresh is most useful for:

• fast powerboats, where the picture must track reality — see motor yacht navigation
• close manoeuvring in traffic or a narrow entrance
• high-relative-speed targets, such as crossing shipping

On a 6-knot yacht, 24 RPM is workable. On a 25-knot boat it is not.

#Sea clutter

Waves return radar energy, producing a bright disc around the vessel that can hide small targets close aboard.

Clutter suppression reduces it, and here is the trap: aggressive clutter suppression also suppresses real weak targets. The small timber boat and the low dinghy are exactly the returns that get removed.

The discipline is to learn what your radar looks like honestly in different sea states, so that when the screen is clean you know whether the water is empty or the gain is wrong. This is the core of the radar tuning guide.

#Rain

Rain attenuates radar energy and can obscure targets within it. It is also information.

Radar can show squalls, rain bands and storm cells, which for tropical and northern Australian cruising is extremely valuable. A squall line visible at eight miles gives time to reduce sail, close hatches and warn the off-watch crew.

Read the rain rather than simply suppressing it: which way are cells tracking, and is the gap you were aiming for still there in ten minutes?

#Radar overlay

Overlay places radar returns over the chart, and it is both an operational aid and a free diagnostic.

When the chart coastline and the radar coastline align well, you have simultaneous confirmation of heading, radar alignment, GNSS position and chart positioning. Four systems cross-checking each other in one glance.

When they do not align, something is wrong, and finding out which is genuinely useful:

• consistent rotational offset → heading misalignment, calibration error, or the wrong network source
• offset that grows in a turn and settles → sensor lag or rate-of-turn issues
• radial mismatch with correct bearings → radar range or timing adjustment

#Heading quality

Bad heading data makes a good radar appear bad.

Radar overlay and target tracking both depend heavily on heading, and a six-degree error is invisible on the display while corrupting every MARPA solution. Before blaming the radar, verify the heading source — and correct it there rather than compensating inside the radar, which hides a fault that is also corrupting true wind and the autopilot. See heading sensors.

#MARPA

Mini Automatic Radar Plotting Aid. Acquire a target and the system estimates:

• target course
• target speed
• CPA — closest point of approach
• TCPA — time to that point

Accuracy depends on your own heading, your own speed, a stable radar return, and the target not manoeuvring. Treat the vectors as dynamic estimates, not measurements: the solution takes time to settle, degrades when the target alters, and can swap identities between two targets that cross close together.

#Current radar families

#HALO20+ and HALO24

Strong B&G and Simrad options with solid-state pulse compression and Doppler VelocityTrack. HALO24 is particularly attractive for serious offshore cruising where size and budget allow.

#Garmin Fantom

Strong Garmin-integrated radar using MotionScope Doppler, in dome and open-array forms.

#Raymarine Quantum 2

Compact solid-state Doppler radar, a natural match for cruising yachts using Axiom.

#Raymarine Cyclone

Open-array solid-state radar for larger vessels.

#Furuno DRS-NXT

A radar-first option with sophisticated target processing and tracking across the family.

#Editorial fit

#Sailing-yacht mounting

#Mast

Pros: the best radar horizon available on the boat, which as noted above is the dominant factor in detection range.

Cons: weight aloft, difficult servicing, cable run through the mast, and complications whenever the rig is pulled.

#Stern pole or arch

Pros: easy service from the deck, shorter cable, no rig involvement, and a position that survives a dismasting.

Cons: lower horizon, and possible obstruction by the boom, bimini or davits.

Serviceability is more important than many buyers expect. A radar you cannot reach is a radar you will not maintain, and on a cruising boat far from a dealer that becomes the deciding factor more often than the horizon does.

Whichever you choose: level within tolerance in the vessel's normal trim, clear of the sail plan, and observing the manufacturer's safe-distance guidance for the transmitting beam — a genuine consideration on smaller boats where the antenna may be near head height.

#Training

Use the radar in clear weather. This is the single highest-value thing you can do with it, and it is free.

Practise identifying:

• a headland — strong, shaped, matching the chart
• a buoy — small, discrete, in the charted position
• a yacht — weak, intermittent, fading between sweeps
• a ship — strong, steady, usually on AIS too
• rain — diffuse, moving as a mass, soft-edged

And cross-compare visual, chart, radar and AIS on the same target until the mental model is automatic. When those four agree you are calibrating your judgement; when they disagree, that is information worth investigating.

Do not wait for fog to learn the interface. Nobody has ever succeeded at that. See the radar tuning guide for the full walkthrough.

#Bottom line

For most 35 to 50 ft cruising yachts: a modern solid-state Doppler radome, integrated with a quality heading sensor, mounted where it can be serviced, and used routinely in clear weather so that it is a familiar instrument rather than an unfamiliar one on the night you need it.