Radar Navigation in Coastal, Narrow and Special Waters

Radar in coastal waters

In short: along the coast the dangers are close, so radar is used for fixing, continuous monitoring and keeping clear of dangers — and a management-level officer must also monitor and supervise how the watchkeepers use it.

Supervising the watch

• Fix, navigate and keep clear of dangers using natural and artificial landmarks, so you can back up the OOW at any moment.
• Spot false or misleading marks caused by coastal interference. Clean the picture up with gain, brilliance, clutter controls, pulse length and display mode, by comparing with the chart, and with the ECDIS–radar overlay.
• Use radar fixes to check how reliable the GPS is.
• Verify the position at suitable intervals by combining EPFS positions, landmark fixes and the estimated track (error analysis).
• Supervise the OOW’s set-up of leading lines, parallel index (PI) lines and risk-avoidance (clearing) lines.
• Treat radar navigation as a supplementary means and know its limits.
• Small isolated landmark as the reference? Track it with ARPA/TT as if it were a target. Keep its CPA at or above the risk-avoidance range while you hold the planned COG.

Radar as the independent check

• Radar and ECDIS do not share inputs. The ECDIS position comes from GNSS; radar ranges and bearings come from your own scanner. An EBL and VRM fix on landmarks, compared with the GPS position, is a genuine cross-check.
• In a bridge team, whoever is not conning or steering keeps confirming the position this way.
• Before trusting a radar fix, check the identity of the fixed object, the overall radar performance, the gyro error and the heading-marker alignment (MGN 379 (M+F)).
• Doubtful target? Switch the ECDIS overlay and synthetics off and look at the raw radar. An input error can lay chart graphics over a real hazard and hide it.

Display mode and stabilisation

• Near fixed objects with north at the top, use true motion, north-up (ground-stabilised). Land and fixed marks stay still; own ship moves across the screen.
• Memory aid: navigation → true motion · collision avoidance → relative motion.
• On a coastal passage use ground stabilisation. When traffic builds up you may switch to sea stabilisation and show true and relative trails or vectors together. There is no single right answer — what counts is that you can justify your choice. Switching underway takes seconds.

Know the limits

• Radar is limited by line of sight, affected by weather and weak on small or poor targets.
• It is not always accurate and not immune to other radars. Its reliable range is about 24 NM — not unlimited, even in open sea.

Narrow waters

In short: little room and little time — plan a contingency for every leg, know your point of no return, and treat the radar picture in bends with suspicion.

Planning the passage

• Every leg carries its own contingency plan: navigation method, risks and precautions. Real passage plans often lack one — make sure yours has it.
• Know the point of no return of each restricted stretch. Past it there is no room to stop or turn: the ship is committed. This matters most for sluggish single-screw ships.
• Rivers often have turning basins (e.g. Antwerp, the Humber, Kiel) that act as escape options.
• A vessel proceeding along a narrow channel keeps as near to the outer limit on her starboard side as is safe and practicable (COLREG Rule 9(a)).

Radar in bends

• The shoreline can hide targets behind it.
• Radar data are less accurate, false echoes are more likely and same-frequency interference from other radars increases.
• → Treat the picture as less reliable and look out of the window.

Fog in a channel

• Example: dense fog, a large container ship 2.5 NM ahead, CPA 0.8 NM, no answer on VHF.
• Right action: reduce speed and prepare to take avoiding action. In restricted visibility there is no stand-on vessel (COLREG Rule 19).
• Wrong: keep course and speed; speed up and overtake to starboard (you are not overtaking). “Head-on” in the wording only tells you the target is forward of the beam.
• Rule of thumb for collision situations: reduce speed.

Traffic separation schemes and VTS areas

In short: a TSS separates opposing traffic; a VTS watches it from ashore. Both mean dense traffic, so navigation dangers and collision risk come together and without a break — experienced supervision is close to indispensable.

What they are

• TSS (traffic separation scheme): a routeing measure that separates opposing streams where traffic is dense or the water restricted. Conduct in and near a scheme: COLREG Rule 10; routeing measures: SOLAS V/10.
• Crossing a lane: on a heading as nearly as practicable at right angles to the general direction of traffic flow (COLREG Rule 10(c)). Cross-Channel ferries in the English Channel are the classic case.
• VTS (vessel traffic service): a shore service that monitors and tracks vessels in a defined area — usually a port approach — and builds its traffic image largely from AIS (SOLAS V/12).

Using radar, ECDIS and AIS together

Use all three to identify:

• the shoreline and capes, and racons;
• TSS entry and termination points;
• buoys, traffic lanes, separation zones and roundabouts;
• inshore traffic zones (ITZ) and precautionary areas;
• isolated danger marks and cardinal marks.

Report abnormal aids to navigation, obstructions and derelicts to the VTS.

VTS reporting points

• The whole bridge team must know where the reporting points are.
• Make them hard to miss: remarks or alarms on the radar map ahead of each reporting line, or extra PI lines as reminders.
• Follow VTS instructions — the VTS sees the wider picture.
• Malta: Valletta VTS — VHF Ch 12 · Marsaxlokk VTS — VHF Ch 14, each with its own reporting area (Transport Malta Coastal Notice to Mariners on Malta VTS). Valletta VTS may give priority to large passenger ships, so a departing vessel can be told to stand by.
• No business in a VTS area and a detour is practical? Stay out — you avoid both the reporting workload and the port traffic.

Why ships come to grief here

• Causes that keep appearing in accident reports: inadequate lookout, decisions on scanty radar information (COLREG Rule 7(c)), misidentified marks and over-reliance on radar, ECDIS and AIS.
• The best navigation tool is still looking out of the window.

Radar in ice-infested waters

In short: ice is a poor radar target — use radar as one source only, on short range scales, with both X- and S-band, and remember that no echo does not mean no ice.

Training and information

• Polar training (STCW and the Polar Code): Advanced Polar (IMO model course 7.12) at management level · Basic Polar (7.11) for junior officers.
• Key reference: The Mariner’s Handbook (NP100).
• NAVTEX ice reports are message type C. Types A, B, D and L cannot be switched off on the receiver.
• Weather services and apps add to the picture — all part of “all available means” (COLREG Rule 5).

How ice shows on radar

• Cold does not harm the radar — but never rely on radar alone for ice; visual observation is preferred.
• Ice and snow reflect far less than steel: ice is a poor target beyond 3–4 NM; best working scale 2–3 NM.
• Flat ice bounces the pulse away like a mirror and gives little or no echo unless it has height (bergs, bergy bits, growlers). Low ice is still dangerous.

Radar settings for ice

• Adjust the gain with care.
• More power helps: a 50 kW set beats a 25 kW one.
• X-band shows more ice detail at short range (under 4 NM, short pulse). S-band detects ice and ridging further out. → Use both.
• Some radars have presets (harbour / open sea / ice). Dedicated ice navigation radars with enhanced 12-bit digital video show bergy bits and growlers far better — a standard set cannot match them with an “enhance” button.
• On X-band at 3 NM, speckle around own ship may just be sea clutter → confirm by lookout.

Icebergs

• Usual detection range: 4–15 NM, more for large bergs. A large berg with a cliff face may show at 15–20 NM; a small, low berg perhaps only at 3–4 NM.
• Low, smooth or snow-covered bergs give weak echoes. A berg may show only as a clutter-free shadow behind it; a gently sloping berg may not show at all.
• Bergs have underwater spurs → give them a wide berth.

Fixing in ice

• Ice along the shore hides the real coastline → take ranges and bearings with extra caution.
• Buoys are unreliable: dragged, hidden by ice or removed for the season.
• Charts of ice areas are often less accurate (short survey seasons) — do not over-rely on them.

Ship handling and signs of ice

• Ice-class ships have a reinforced ice belt at the waterline — about ±0.5 m around the summer draught, plating 3–5 times thicker.
• Enter ice at minimum speed. Avoid getting beset — head slowly for open water.
• Ice is near when: strong wind but no waves (no fetch over ice → pack ice upwind) · sea temperature drops · unexpected wildlife (gulls far offshore, resting on ice).

Choosing an anchorage and keeping an anchor watch

In short: choose the spot from chart and VTS, measure distances before letting go, record the let-go data, then watch fixed targets for dragging — alarms help, the lookout decides.

Approach and letting go

• Choose the anchorage from the chart and VTS information.
• Set the range scale to suit the distance to the anchorage and how crowded it is.
• Measure the distance to other anchored ships before letting go.
• Think in swing circles, not drop points. Anchor astern of a larger ship that has already settled (chain stretched out) rather than near one that has just let go.
• Most of the holding comes from the weight of the chain.

Once anchored

• Record heading and GPS position at the moment of letting go, then the length of chain paid out.
• Fix the position on conspicuous objects — plot a real fix (ranges and a bearing) even when GPS and radar give a readout.
• Set the anchor watch alarm (radius and centre) from wind, waves, current and chain length. Caution: errors come from the anchor dredging before it bites and from the catenary of the chain.
• Set a guard zone to warn of approaching ships, in case either of you drags.
• An anchor alarm built with the radar maps function is only as accurate as the position-fixing system behind it.
• Caution: guard zones and alarms are aids only — the visual lookout goes on.

Checking for dragging

• Watch range rings, VRM and ERBL on fixed targets: ranges and bearings that keep changing mean the ship is moving.
• Some radars have an anchor mode (anchor icon). Its radius is the swing circle; leaving it gives a visual alert, then an audible one, possibly repeated in the Master’s cabin.
• No anchor mode? Centre a VRM on the anchor position (not on own ship) to mark the swing circle.
• Rough example: in 10 m of water with 40 m of chain, the chain reaches about 35 m horizontally. The circle traced by the position reference also includes the distance from the hawse pipe to where the position is taken.
• Other checks: transits and PI lines on the coastline, the GPS anchor alarm, SOG and COG, and a visual check of the chain (direction, vibration).

Berthing and unberthing with radar

In short: radar gives numbers for timing engine, thrusters, rudder and anchor — on a very short range scale — but the people at the mooring stations remain the best source.

Radar tools alongside

• Change the range scale for each phase. Berthing: 0.25–0.5 NM, at most 0.75 NM — the 1.5, 3, 6 and 12 NM scales are useless at the berth.
• VRM: distance to ships and obstructions ahead and astern, to the berth line, and timing for dropping the outside anchor.
• EBL or PI line: monitor the angle of approach to the berth.
• ECDIS predictor vectors show sideways motion and the turning path over the next few minutes.

Limits and other sources

• Know your blind and shadow sectors — the berth line may give no echo at all.
• Caution: radar range is the slant distance from scanner to object, not the horizontal distance — this matters very close to the berth.
• Reports from the mooring stations forward and aft (“clear to swing”, “x metres off”, “parallel to the breakwater”) are the best information and are preferred to radar for distances fore and aft.
• CCTV angles can mislead, and cameras fail.
• Current changes everything at low speed: a slow ship may make 12–13 kn over the ground at full ahead with the current and only 6–7 kn against it.

Worked scenario: night passage through an archipelago

In short: in narrow channels at night in rain, radar is the primary source — prepare the plan and the equipment first, keep the speed down, plan the turns and expect failures.

Situation: a 50 m motor yacht, draught 3 m, in the Stockholm archipelago at night, in restricted visibility with rain and light wind. About 13.9 NM to the destination, 40 minutes available.

Before getting underway

• Prepare a passage plan from the present position to the destination, and check it.
• Switch on all radars, AIS and ECDIS and check each for faults.
• Run the ECDIS route check and read every hazard it reports. Some are irrelevant, e.g. caused by a wrongly set safety contour; make sure the draught entered is correct.
• Set the rain clutter for the conditions.
• Load the route on the radar as well.
• Restricted-visibility routine: inform the Master, navigation lights on, fog signals, radar in use, extra lookout, safe speed and engines ready for immediate manoeuvre (MGN 315 (M); COLREG Rule 19(b)).

Through the channels

• Radar is the primary source: a continuous series of EBL/VRM bearings and ranges, PI lines where they help, and the ENC overlay as back-up.
• Stabilisation: ground-stabilised for the coastal passage; with traffic around, sea-stabilised with true and relative trails/vectors — as long as you can justify it.
• Keep to the starboard side of the channel (COLREG Rule 9(a)).
• Full speed is not required: slow down, or depart from the planned track and speed, whenever needed.
• Plan the turns: at speed, ships tend to swing wide in the bends → use wheel-over positions.

Expect failures

• Be ready for a loss of steering and an invalid position alert in the middle of the passage.
• Keep scanning every display for new flashing alerts, and listen for sound signals from outside.