Restricted Visibility (Part 1)

Q. In restricted visibility you find a target 5 miles off, 3 points on starboard bow. What is your action?
Ans. I assume that all the precautions for restricted visibility are already being taken. Upon detecting a target on my radar screen I will plot the target to know the CPA, TCPA as well as, whether the target is crossing, is being overtaken or is a stationary target. This situation is governed by rule 19 (d) of the COLREGs, as per this rule I shall determine if a close quarter situation is developing and/or risk of collision exists. I will take appropriate avoiding action in ample time, which normally would be an alteration of course to starboard for a target that is crossing. In certain cases I will reduce the speed.

Q. But by altering to starboard you may be closing in the vessel on starboard bow!
Ans. The target on the starboard bow is also likely to alter to her starboard because I am converging with her, from forward of her beam and I am not being overtaken. This means the target alters to her starboard and I alter to my starboard.

Q. Why shouldn’t you alter course to port?
Ans. As per rule 19(d) of COLREG, in case of alteration of course, so far as possible I shall avoid an alteration of course to port for a vessel forward of the beam, other than for a vessel being overtaken.

Q. Won’t you give the maneuvering signal before alteration?
Ans. In restricted visibility maneuvering and warning signal are not given. The sound signals given in rule 36 i.e. one prolonged blast at intervals of not more than 2 minutes is sounded at all times.

Q. How much alteration to starboard is needed?
Ans. With the present distance of 5 miles between the 2 vessels and a relative approach speed of say 8 kn, TCPA may be about 35 minutes. As guided by the principles of rule 8, an alteration of 400-500 should be appropriate.

Q. In which situations will you alter to port for a vessel forward of your beam and coming down and converging course?
Ans. 19(d) of COLREGs, uses the term ‘so far as possible avoid an alteration of course to port’. This means, there are some situations where circumstances might demand an alteration to port. Thus, when the target is closing in from up to about 2 points forward of starboard beam or there is shallow water on starboard side or there is a ship very close on starboard beam/quarter, an alteration of course to starboard will cause possibility of grounding or a close quarter situation. Though, if an alteration of course to port is decided, such alteration of course to port must be very bold and made in good time so that it is evident to the other vessel, , observing on radar in good time.

Q. In fog, with your radar operational and target on starboard bow on a converging course, what is the possible action by the target vessel?
Ans. If the target vessel detects my ship on her radar, and takes action by altering her course, it will be to her starboard as per rule 19 (d). She might also reduce her speed. In either case, my altering to starboard will take my vessel away from her. She would be clear on my port side even if she maintains her course and speed.

In case the target does not have an operational radar, she would reduce her speed to minimum at which she can be kept on her course. Even this action of the target vessel is compatible to my alteration of course to starboard.

Q. You, having taken action in fog as per rule 19 (d), subsequently, spot the target vessel visually. Will your action change now?
Ans. Generally, the good visibility actions are compatible to a restricted visibility actions taken earlier. Thus, in above case, if I visually find the target vessel one mile off on my port side, she would be seen with red aspect. There will be no problem in continuing with the original action. Hence, on subsequent spotting of target vessel visually, no contradictory action should be required by any vessel.

Q. What is close quarter situation?
Ans. Rule 8 (c), 19 (d), 19 (e) refer to close quarter situations. The distance at which a close quarter situation first applies has not been defined in the rules and is not likely to be defined as it will depend on number of factors, such as size, characteristics and speed of other ships in question. It must also depend on the visibility, state of sea, traffic and the limitation caused by depth and topography of the area. As a rough rule of thumb, at least two miles, which is the audible range of vessel in the directions forward of beam in restricted visibility can be the distance. Some consider 3 miles to be their limiting distance. Close quarter distance can be much less for a vessel that is overtaking. Suppose own ship is at 6 kn and other ships in the vicinity are also maneuvering at about 6 kn (say +/- 10 %) and are at a distance of 3 miles each. The TCPA for a forward vessel may be 12 minutes where as for a vessel that is overtaking, it may be 90 minutes.  Obviously, the close quarter distance for the overtaking vessel is much less than the close quarter distance for the vessels on converging or reciprocal courses.

Q. If you have two radars, on what ranges will you keep them for navigation in fog?
Ans. With two radars, I would want to use one radar on 3 miles range and other on 12 miles range. The radar on 3 miles range is basically to detect small targets, which sometimes, can go undetected at higher ranges. Setting for anti clutter and tuning must however, be adjusted properly. As a rough rule, on the second radar, used on 12 miles range scale, a target should be assessed till say 9 miles off, to see whether a close quarter situation is developing. If so, substantial action should be taken before the target is less than 4 miles off.

Q. What is more appropriate to avoid close quarter situation; change of course or reduction of speed?
Ans. Alteration of course can be directly executed from the navigational bridge. Alteration of speed on the other hand, is mostly executed from engine room. Moreover, the alteration of speed involves more human intervention as compared to the alteration of course. Also, alternate means of steering are available in case one mode fails.

Alteration of course is immediately noticeable to the other vessel in good visibility. Reduction of speed on the other hand is not visually noticeable.

Most people prefer alteration of course to the reduction of speed. Duty officer though, may prefer reduction of speed alone or such reduction in combination with alteration of course in certain situations. Thus, if a converging ship is detected on radar screen, in fog on 1 or 2 points on starboard bow and is on collision course, a 30o to 40o of alteration to starboard will be sufficient at a distance of say 5 miles. But, if the target was on one point forward of starboard beam, the alteration required to starboard could be as much as 150o to avoid close quarter situation. It is interesting to note that alteration of course automatically causes some reduction of speed.

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