How to Tune Marine Radar

Radar is the only recreational navigation technology that independently observes the physical world. It is also the one most often fitted, never tuned, and switched on for the first time in fog.

This walkthrough fixes that. Everything below happens in clear weather.

#Before you touch a radar control

Verify the heading source. This is not a radar step, and it comes first anyway.

Overlay radar on the chart near a well-charted coastline. If the radar coastline is rotated relative to the charted one, you have a heading problem — misalignment, calibration error, sensor lag, or the network using the wrong source. As the heading sensors guide puts it, treat heading as infrastructure: it feeds the autopilot, radar overlay, MARPA, true wind and laylines simultaneously.

Fix it there. Compensating inside the radar buries a fault that is corrupting four other systems.

#The order to set it up in

#1. Range

Run two ranges and alternate deliberately:

• Short, about 0.5 to 1.5 NM — immediate collision risk and close pilotage
• Medium, 6 to 12 NM — developing traffic and weather

The radar guide makes the case that this is where the value is: advertised maximum range is close to meaningless, and collision and pilotage decisions happen inside 12 NM.

#2. Gain, with suppression off

Turn sea and rain clutter to minimum first, so you are seeing what the receiver actually receives.

Then raise gain until a faint background speckle just appears across the display, and back off slightly.

• Too little gain: weak targets are simply absent
• Too much: real targets disappear into noise

Automatic gain is a reasonable starting point and tends to be conservative in a seaway.

#3. Sea clutter, sparingly

Waves return energy, and near the vessel that produces a bright disc. Suppression reduces it.

The discipline: increase it only until nearby wave returns are reduced, not eliminated. Aggressive suppression also removes kayaks, small timber boats, low dinghies and debris — the exact targets the radar guide warns radar may miss anyway.

Learn what your radar honestly looks like in a moderate sea. A clean screen should mean empty water, not aggressive tuning.

#4. Rain, as information

Rain can obscure targets and is also genuinely useful. Radar showing squalls, rain bands and storm cells is valuable for tropical and northern Australian cruising.

Suppress only enough to see targets within the rain. Then read the rain: which way are cells tracking, and is the gap you were aiming for still there in ten minutes?

#5. Doppler

Enable VelocityTrack, MotionScope, Raymarine Doppler or Furuno Sonar Depth">Target Analyzer and sanity-check it: a vessel you can see approaching should be coloured as approaching.

This is the single biggest reduction in interpretation workload available, and it is why the radar buying guide recommends buying Doppler for any new 2026 install. It does not replace knowledge of the AIS 2026: COLREGs in Practice">collision regulations.

#The part that actually matters: practice

Tuning takes twenty minutes. Competence takes repetition.

In clear daylight, deliberately find and identify:

Cross-check each against visual, chart, radar and AIS. When those four agree you are calibrating your judgement. When they disagree — a strong radar target with no AIS, for instance — that is information, and it deserves more attention rather than less.

Then acquire a MARPA target and watch the solution settle. Learn how long it takes, and how it degrades when the target manoeuvres. The collision avoidance guide covers why a CPA is a prediction rather than a fact.

#What tuning cannot fix

A target below the radar horizon is not there to be found at any gain setting. Antenna height, target height and reflectivity set detection before any control does.

Nor can tuning fix a tilted antenna, a bad cable, or a heading source in the wrong place. Those belong to commissioning and sensor siting.

#Record it

Note the gain, sea and rain settings that gave an honest picture, and in what conditions, in the vessel's commissioning record. Re-check alignment annually and after any mast, antenna or heading work.

#Bottom line

Verify heading, then gain with suppression off, then clutter sparingly, then Doppler — and then spend the real effort on identifying headlands, buoys, yachts, ships and rain while you can still see them.