A 1,000 TEU container vessel, vessel A, was sailing towards the pilot station at 17 knots, with the vessel being in manual-steering mode and on a course of 280°. Given the afternoon hours, the visibility was restricted and there was fog. The bosun on the deck was preparing the pilot ladder, to then proceed to his next duty as a lookout.

On the bridge, the Master had the conn, the Second Officer was the one monitoring and the AB was on the wheel. Two ARPA radars were used alternatively on ranges between 6 NM, 3 NM and 1.5 NM. Both the Master and OOW were monitoring the vessel’s progress on the radars.

During the monitoring, the Master observed a target and acquired it on the ARPA as vessel B. The target was seen being 10° on the port bow, 4 NM away with a CPA of 0.2 NM.

Vessel A was overtaking Vessel B, and was acknowledged that if the former kept its course, it could hit vessel B on the starboard side. Given that vessel B was on a course of about 280° and making a speed of 6 knots, the master of vessel A began the fog signal.

Minutes before collision

C-15 minutes: Vessel B was on course of 293° and the CPA was 0.14 NM. Vessel A was maintaining its course and speed.

C-10 minutes: Vessel B’s course was 285°, CPA 0.04 NM and distant 1.4 NM.

C-5 minutes: Vessel B’s course was 289°, CPA 0.03 NM and distant 0.65 NM.

C-2 minutes: Vessel B’s course was 304° and CPA 0.01 NM and distant 0.3 NM. Vessel B was still on the port bow of vessel A. At this point the Master on vessel A realized that vessel B was very close and ordered hard to-starboard and stop engines.


Due to the proximity of both vessels, it was too late to avoid the collision, as vessel A hit vessel B on its starboard side about midships. Vessel B, a small tanker, began listing after the collision and its crew had to abandon the ship, deploying life rafts.

The crew of vessel B were then rescued by vessel A.


Following the incident above, the Swedish Club cites six COLREGs to explain what were the wrong steps taken that resulted to the two vessels colliding.

Rule 5 - Look out: Every vessel shall at all times maintain a proper look-out by sight and hearing, as well as by all available means appropriate in the prevailing circumstances and conditions, so as to make a full appraisal of the situation and of the risk of collision.

In this collision neither vessel seems to have maintained proper lookout.

Rule 6 - Safe speed: Every vessel shall at all times proceed at a safe speed so that she can take proper and effective action to avoid collision and be stopped within a distance appropriate to the prevailing circumstances and conditions. In determining a safe speed, the following factors shall be among those taken into account: (a) By all vessels: (i) the state of visibility

The OOW must have time to take proper and effective action to avoid collision as required under Rule 6 to be considered to have proceeded at safe speed. Vessel A was making a speed of 17 knots in restricted visibility while approaching a congested area and a pilot station and this would probably be considered not to be a safe speed in the prevailing circumstances. This is also emphasised in Rule 19.

Rule 7 - Risk of collision: (a) Every vessel shall use all available means appropriate to the prevailing circumstances and conditions to determine if risk of collision exists. If there is any doubt (then) such risk shall be deemed to exist. (b) Proper use shall be made of radar equipment if fitted and operational, including long-range scanning to obtain early warning of risk of collision and radar plotting or equivalent systematic observation of detected objects.

Vessel B was plotted on the ARPA on board vessel A and showed a small CPA. Despite the small CPA, no action was taken by the bridge team on vessel A.

At about C-15, the CPA to vessel B was 0.14 NM, which indicated that a risk of collision existed between the vessels. Visibility was restricted and so it was even more important to ensure that the CPA was large enough to account for any margin of error in the equipment. As per ARPA performance standards regulation the CPA should be calculated by the ARPA within three minutes with an accuracy of within 0.5 NM. This means that if the ARPA reports a CPA of 0.5 NM the actual CPA could be 0.0 miles or 0.5 miles. The bridge team must factor in this margin of error of the CPA when planning any collision avoidance manoeuvres and the passing distances to other vessels.

Rule 8 - Action to avoid collision: (e) Any action taken to avoid collision shall be taken in accordance with the Rules of this Part and shall, if the circumstances of the case admit, be positive, made in ample time and with due regard to the observance of good seamanship.

(f) Any alteration of course and/or speed to avoid collision shall, if the circumstances of the case admit, be large enough to be readily apparent to another vessel observing visually or by radar: a succession of small alterations of course and/or speed should be avoided.

It is prudent and good seamanship to take action at an early stage by altering course and/or reducing speed to open up the CPA. In this case neither vessel took any action to avoid collision.

Rule 13 – Overtaking: (a). Notwithstanding anything contained in the Rules of part B, sections I and II, any vessel overtaking any other shall keep out of the way of the vessel being overtaken.

Vessel A was overtaking vessel B.

Rule 19 Restricted visibility – (a) This Rule applies to vessels not in sight of one another when navigating in or near an area of restricted visibility. (b) Every vessel shall proceed at a safe speed adapted to the prevailing circumstances and conditions of restricted visibility. A power-driven vessel shall have her engines ready for immediate manoeuvre. (d) A vessel which detects by radar alone the presence of another vessel shall determine if a closequarters situation is developing and/or risk of collision exists. If so, she shall take avoiding action in ample time, provided that when such action consists of an alteration of course, so far as possible the following shall be avoided: (i) an alteration of course to port for a vessel forward of the beam, other than for a vessel being overtaken: (ii) an alteration of course towards a vessel abeam or abaft the beam.

In restricted visibility both vessels have a requirement to stay clear of each other. It is likely that vessel B was altering course as per her passage plan. It is still the responsibility of vessel A to ensure they stay clear of vessel B as per Rule 19.

 Lessons Learned

  • The bridge team on vessel A acquired vessel B on the ARPA at about C-15 minutes. The CPA was 0.14 NM. With such a small CPA this should be considered a close quarter situation, meaning that at this point the crew had to take preventive measures to avoid the collision, with both vessels taking no preventive measures.
  • When sailing in restricted visibility all vessels have a responsibility to stay clear of each other. All vessels also have a responsibility to proceed at a safe speed which ensures that they can stop quickly. Maintaining full speed in restricted visibility under these navigational circumstances could be considered proceeding at an unsafe speed.
  • In restricted visibility both vessels have an obligation to stay clear of each other. However, we do not know why vessel B altered to starboard. It is possible vessel B altered course in accordance with their passage plan. Vessel A was overtaking vessel B which required vessel A to stay well clear of vessel B.
  • It is important that the officers understand the rules and increased risks when sailing in restricted visibility. It is also important to understand the limitations of the navigation equipment. It appears that the bridge team on vessel A considered a CPA of 0.14 NM to be an acceptable CPA. To ensure situational awareness is maintained, the bridge team should discuss all plotted targets, what risks they pose and take appropriate action.