Bridge Watchkeeping: ECDIS, ARPA and BRM

Prerequisites

You should know the COLREGs and radar basics from the RYA courses (the radar and collision avoidance lessons), including the meaning of CPA and TCPA, and you should have kept night watches on a yacht. This lesson shows how the same principles scale up on a merchant ship, where the officer of the watch (OOW) may be conning 200,000 tonnes at 15 knots with a crew of one lookout.

Learning Objectives

Describe the main bridge equipment on a merchant ship and what each item is for.
Explain what ECDIS is, why it needs both generic and type-specific training, and which settings make it an active safety tool rather than a passive picture.
Explain how ARPA derives CPA and TCPA, and the errors that make those numbers wrong.
State the OOW's duties as set out by the MCA in MGN 315, including handover, lookout, restricted visibility and anchor watch.
Describe bridge resource management (BRM), including working with a pilot.
Learn from real MAIB accident cases where these duties broke down.

The Bridge

A modern bridge typically has two radars (an X band set at 3 cm wavelength for sharp detail and an S band set at 10 cm that sees better through rain and sea clutter), ECDIS (electronic chart display and information system), GNSS receivers, gyro and magnetic compasses, autopilot and track control, AIS, echo sounder, speed log, GMDSS radio station, the BNWAS (bridge navigational watch alarm system) and a VDR (voyage data recorder, the ship's "black box", which records radar images, positions, audio from bridge microphones and VHF).

BNWAS exists because watchkeepers fall asleep. If the OOW does not reset it within a set dormant period (3 to 12 minutes), it alarms on the bridge, then in the master's and back-up officer's cabins, then more widely. A BNWAS that has been switched off or wedged is a sign of a dangerous bridge culture.

The Officer of the Watch

The MCA's guidance on keeping a safe navigational watch is MGN 315, which applies STCW and points to the ICS Bridge Procedures Guide as the principal guide to good practice (MGN 315, para 1.4). Its core message: the OOW is the master's representative and is primarily responsible at all times for safe navigation and for complying with the COLREGs (MGN 315, para 2.1).

Duties on watch

MGN 315 (para 4.1) says the OOW shall:

Keep the watch on the bridge and never leave it until properly relieved.
Remain responsible even when the master is on the bridge, until the master says specifically that they have the con and this is mutually understood.
Remain responsible even with a pilot on board; if in doubt about the pilot's actions, ask the pilot, and if doubt remains, call the master and act as needed until they arrive.
Call the master whenever in doubt about what action to take.
Not take on other duties that compromise the watch, and avoid distractions from radios, computers and mobile phones.
Have a qualified helmsman available at all times, and put the ship in hand steering in heavy traffic, restricted visibility and any hazardous situation, early enough that the OOW is not forced to break the lookout to take emergency action.
Use the radar at all times in heavy traffic and whenever restricted visibility is encountered or expected, and practise with it in clear weather to learn its limits.
Fix the position at frequent intervals, by more than one method whenever possible, on the largest scale chart, corrected up to date including navigational warnings and temporary and preliminary notices.

The engines are at the OOW's disposal and there should be no hesitation in using them (MGN 315, para 2.4). Give the duty engineer notice when you can, but a call to the engine room is never a reason to delay slowing down.

The lookout

COLREG Rule 5 applies exactly as on a yacht. The MCA adds that it considers it "dangerous and irresponsible" for the OOW to be the sole lookout in darkness or restricted visibility, and that STCW implies a separate dedicated lookout whenever a ship is under way (MGN 315, paras 2.6 and 2.7). The helmsman is not the lookout, except on small vessels with an all-round view from the steering position (para 8.2).

The master may allow the OOW to be sole lookout only in clear daylight, and only after assessing weather, visibility, traffic, nearby dangers, TSS proximity, bridge layout and blind arcs, the radars fitted, and distractions such as GMDSS, email, logs, chart corrections and equipment tests. Help must be immediately available to summon (MGN 315, para 8.3). Treat the lookout as part of the bridge team: tell them what traffic, buoys and landfall to expect (para 9.2).

Handing over and taking over

The OOW must not hand over to a relief who appears unfit (call the master instead), or while a manoeuvre is in progress, and must make sure the relief's eyes have adjusted to the dark and they understand the standing and night orders (MGN 315, section 6).

Before accepting the watch, the relieving officer should (MGN 315, section 7):

Verify the ship's position.
Confirm the intended track, course and speed.
Note dangers expected during the watch.
Know the tides, currents, weather and visibility and their effect on course and speed.
Note gyro and magnetic compass errors.
Note the status of all bridge equipment.
Note bridge and engine control settings and engine room manning.
Know the vessels in sight or nearby and how they are moving.
Brief the watch team, including the lookout.

Restricted visibility and safe speed

When visibility closes in, the OOW must comply with the COLREGs (lookout, fog signals, safe speed, engines ready), and in addition inform the master, post a dedicated lookout, show navigation lights, use the radar and put the engines on standby (MGN 315, section 10). No commercial pressure justifies excess speed: MGN 315 (para 11.4) cites The Lady Gwendolen, where the Court of Appeal called excessive speed in fog "a grave breach of duty" and the owners lost the right to limit their liability.

At anchor

The anchor watch plots the position as soon as practicable, checks it regularly with bearings and transits, keeps a lookout, makes rounds, watches weather and tide, keeps engines at the readiness the master requires, and calls the master if the anchor drags. MGN 315 (para 12.1) says relying on radar guard zones instead of a lookout is not acceptable.

Fitness and certification

Watchkeepers must be rested (at least 10 hours of rest in any 24 and 77 in any 7 days) and free of alcohol and impairing medication (MGN 315, section 3). The MCA notes that MAIB reports show how easy it is to fall asleep sitting down in an enclosed wheelhouse: stand, move and ventilate. Every rating on a navigational watch on a ship of 500 GT or more needs a Navigational Watch Rating Certificate (STCW A-II/4; MGN 315, para 13.2).

ECDIS

ECDIS displays official electronic navigational charts (ENCs) and, once a ship has an approved ECDIS with back-up, it is the primary means of navigation. SOLAS phased in mandatory carriage on most new and existing cargo and passenger ships between 2012 and 2018. Officers need a generic ECDIS course (an MCA-approved IMO model course to STCW standard, which is a prerequisite for UK deck certificates if not covered in training, MSN 1856, section 10) and type-specific familiarisation on the make fitted, because menus and alarm logic differ.

Settings that make ECDIS work for you

Safety contour: the depth contour that separates safe from unsafe water for this ship. Set it from draught plus squat plus an under-keel clearance margin. ECDIS uses the next deeper charted contour if the exact value does not exist.
Safety depth: highlights individual soundings shallower than this value.
Route check: run the automatic check against the safety contour and danger areas, then visually check the route at the largest scale. Many groundings followed a check made at a small scale where dangers were not shown.
Alarms: cross-track error, waypoint approach, off-track and anti-grounding look-ahead. Set the look-ahead to cover several minutes of steaming.
Data quality: ENCs show survey reliability as CATZOC (category of zone of confidence), not the familiar source diagram.

Case study: a 19th century survey (MAIB Safety Digest 1/2008, Case 1)

A tug towing a jack-up barge grounded where the chart showed more than 20 m. A later survey found an uncharted bank of about 7 m. The chart's source data was a leadline survey from 1844, which had simply missed the bank. The MAIB lesson: check the source data of your charts when planning; on ECDIS that means CATZOC, which may be buried in a menu and easily forgotten, while basic chart plotters may not show it at all.

Case study: the passive electronic chart (MAIB Safety Digest 2/2007, Case 10)

On a container feeder at night, the second officer sent the lookout below half an hour into his midnight watch, then became absorbed in mobile phone text messages for over 40 minutes. He missed the planned 0115 alteration and the ship grounded about half an hour later, holing two ballast tanks. The electronic chart system had no depth areas, cross-track or waypoint alarms set, so it gave no warning. The lessons: never stand the lookout down at night, have a clear mobile phone policy on the bridge, and set the alarms that turn an electronic chart from a picture into a safety net.

ARPA Radar

ARPA (automatic radar plotting aid) tracks selected targets and calculates their true course and speed, CPA (closest point of approach) and TCPA (time to CPA). It does automatically what the manoeuvring board does by hand: it observes the target's successive relative positions, draws the relative motion line, and finds where that line passes closest to own ship (NGA Pub 1310 explains the plot). Relative motion is what tells you about risk; true motion tells you the target's aspect and what action it may take.

Making ARPA numbers trustworthy

Heading and speed inputs: ARPA calculates true vectors from own ship's gyro heading and log speed. A gyro error or a log reading speed through water in a strong tide gives wrong true vectors and can show a crossing ship as head-on, or vice versa. Relative vectors and CPA are less affected by these errors.
Time to settle: a newly acquired target needs about one minute for a trend and about three minutes for a reliable prediction.
Target swap and loss: tracks can jump to a nearby target or drop in clutter. Watch for them.
Clutter: auto clutter can suppress small targets such as fishing vessels and yachts. In MAIB Safety Digest 1/2008, Case 6, a tanker in fog did not see a fishing vessel on radar, either because no one was watching it or because auto clutter masked it; the fishing skipper had his radar on 0.125 miles range, about one minute's view ahead. Neither vessel sounded fog signals, and they collided.
Compass bearings: a steady compass bearing and decreasing range still mean risk of collision (COLREG Rule 7). Use visual bearings to confirm.

Companies set minimum CPAs in the master's standing orders, typically 1 to 2 miles in open sea and less in confined waters, together with when to call the master. AIS is an aid: it shows only ships transmitting, can carry wrong data, and its heading and course are not radar observations. It never replaces radar and a visual lookout.

Worked example

At 0300 an ARPA target bears 040 degrees at 8 miles, CPA 0.3 miles, TCPA 20 minutes. Own ship makes 14 knots on 000 degrees. The target is crossing from starboard, so own ship is the give-way vessel (Rule 15). The standing orders say minimum CPA 2 miles and call the master if CPA is under 1 mile. The OOW calls the master, puts the ship in hand steering, and makes a bold alteration to starboard of 30 to 40 degrees, early and large enough to be obvious on the other ship's radar (Rule 8). Over the next three minutes the OOW watches the target's relative track to confirm the CPA is opening past 2 miles, then plans when to return to track.

Bridge Resource Management

BRM is the effective use of all resources, human and electronic, to navigate safely. The US Coast Guard describes it as a safety culture that promotes communication, cooperation and coordination among everyone involved in navigation, and notes it is required under STCW (USCG Safety Alert 09-13). Its tools:

Shared mental model: everyone knows the plan, the next alteration and the hazards. Brief before arrival, departure and pilotage.
Closed-loop orders: "Starboard ten." "Starboard ten, sir." "Wheel's starboard ten." The order is repeated and confirmed.
Challenge and response: a junior officer must voice concern, and the senior must welcome it.
Workload management: call another officer up when the OOW is overloaded. In MAIB 1/2008, Case 6, the tanker master was trying to navigate and communicate alone in fog when he should have called another officer.
Cross-checking: position by two methods; a second person checks every critical setting.

Working with a pilot

A pilot advises and usually conns the ship in pilotage waters, but the master remains responsible for the ship and the OOW still monitors and fixes the position (MGN 315, para 4.1). Begin with a master-pilot information exchange: passage plan, draught, manoeuvring data, tugs, berth, and any defects. Then keep monitoring the track against the plan, check that helm and engine orders are carried out correctly, and speak up early.

The USCG alert describes a deep-draught tanker that struck a bridge in very poor visibility while the pilot navigated with almost no input from the ship's watch team, even though everyone had done BRM courses within five years and the company had BRM procedures. A course certificate is not BRM; communication on the day is.

Case study: a meal break at the wrong moment (MAIB Safety Digest 2/2007, Case 3)

A Panamax bulk carrier dropped her pilot and entered a strait TSS in good visibility. The master went to the back of the bridge for paperwork and took no further interest. The chief officer found the ship south of track and altered 15 degrees to starboard, then handed over to the third officer so he could eat, before the ship had regained track. The third officer took a single radar range and bearing fix, saw the ship back on track at a planned 5 degree alteration, but did not alter course. He also did not positively identify the two cardinal buoys he passed between, which were in fact the marks on either side of the bank. The ship grounded at 15.5 knots. The lessons: do not hand over in the middle of a manoeuvre (MGN 315, para 6.2), positively identify marks, fix by more than one method, and the master should stay engaged in confined waters.

Common Mistakes

Standing the lookout down at night to do another job. MGN 315 and the MAIB are clear: do not.
Handing over during a manoeuvre or with the ship off track.
Setting no ECDIS alarms, or checking the route only at small scale.
Trusting ARPA true vectors with a wrong heading or speed input, or acting on a target before its track has settled.
Relying on AIS to identify every vessel.
Assuming the pilot has it covered. The master and OOW remain responsible.
Sitting down in a warm, dark wheelhouse in the small hours.
Not calling the master for fear of disturbing them. Standing orders exist to be used.

Summary

Merchant bridges carry radar, ECDIS, AIS, GMDSS, BNWAS and a VDR, but the OOW's judgement is still the key safety system.
MGN 315: the OOW is the master's representative, responsible until relieved or until the master clearly takes the con, and responsible even with a pilot on board.
A dedicated lookout is expected whenever under way; the OOW may be sole lookout only in clear daylight with the master's specific assessment.
Take over only after checking position, track, dangers, tides, compass errors, equipment, engines and traffic.
ECDIS needs generic and type-specific training, correct safety contour and safety depth, active alarms and attention to CATZOC.
ARPA gives CPA and TCPA, but they depend on correct heading and speed and need time to settle. Confirm with compass bearings.
BRM is about communication on the day. With a pilot aboard, the master remains responsible and the bridge team monitors.

Check Your Understanding

What is the difference between generic and type-specific ECDIS training?

Answer: Generic training covers ECDIS principles, standards and limitations to the STCW standard; type-specific familiarisation covers the particular make and model fitted, whose menus and alarm logic differ.

What do CPA and TCPA mean, and what input errors can make ARPA's true vectors wrong?

Answer: Closest point of approach and time to closest point of approach. Errors in own ship's heading (gyro) or speed (log, especially through-water speed in a strong tide) distort the target's calculated true course and speed.

When a pilot is on board, who is responsible for the ship, and what should the OOW do if unsure about the pilot's intentions?

Answer: The master remains responsible and the OOW remains responsible for the watch. The OOW should ask the pilot for clarification, and if doubt remains, call the master and take whatever action is needed until the master arrives (MGN 315, para 4.1).

Under MGN 315, when may the OOW act as sole lookout?

Answer: Only in clear daylight, when the master has specifically assessed it as safe, considering weather, visibility, traffic, dangers, TSS, bridge layout, radar and distractions, and with help immediately available. The MCA considers it dangerous and irresponsible in darkness or restricted visibility.

Name five things the relieving officer must check before taking over the watch.

Answer: Any five of: the ship's position; intended track, course and speed; dangers expected; tides, currents, weather and visibility; compass errors; status of bridge equipment; bridge and engine control settings and engine room manning; vessels in the vicinity; and briefing the watch team.

What extra actions does MGN 315 require when restricted visibility is encountered?

Answer: Inform the master, post a dedicated lookout, show navigation lights, operate and use the radar, and put the engines on standby, in addition to the COLREG duties of lookout, fog signals and safe speed.

What is CATZOC and why did the MAIB highlight it?

Answer: The category of zone of confidence, ECDIS's indication of survey reliability. In a 2008 case a barge grounded on a bank missed by an 1844 leadline survey; the MAIB warned that CATZOC may be hidden in menus and forgotten during passage planning.

In MAIB Safety Digest 2/2007, Case 10, which two failures let the ship run aground unnoticed?

Answer: The second officer sent the lookout below and became distracted by his mobile phone, and the electronic chart had no depth, cross-track or waypoint alarms set, so nothing warned him of the missed alteration.

Sources

MCA, MGN 315 (M): Keeping a Safe Navigational Watch on Merchant Vessels (2006).
MCA, MSN 1856 (M) Amendment 1: UK Requirements for Master and Deck Officers.
US Coast Guard, Safety Alert 09-13: Bridge Resource Management in Pilotage Waters (2013).
NGA, Pub 1310: Radar Navigation and Maneuvering Board Manual.
MAIB, Safety Digest 2/2007 (Cases 3 and 10) and Safety Digest 1/2008 (Cases 1 and 6). These digests date from 2007 and 2008, before mandatory ECDIS carriage; their lessons still apply, but equipment and alarm standards have moved on.