Radar 2 Flashcards
Rule 19 Conduct of vessels in restricted visibility
Rule 19 Conduct of vessels in restricted visibility
Ref MGN 369
Navigating a ship in restricted visibility requires a full understanding of the COLREGS, in particular Part B (Steering and Sailing Rules) both Section III (Rule 19) – Conduct of vessels in restricted visibility and Section I (Rules 4 to 10 inclusive) – Conduct of vessels in any condition of visibility.
It is the responsibility of the OOW to comply with the COLREGS. Companies have to ensure compliance of their employees with COLREGS and issue guidance to that extent but the ultimate decision about safe navigation has to be made by the OOW taking into account all available information.
Rule 19 is the basis for navigation in reduced visibility; this Rule requires that a vessel shall proceed at a safe speed adapted to the prevailing circumstances, initially to be judged by all factors listed in Rule 6. Rule 19 requires that there is no stand-on vessel. All participants are required to take appropriate avoiding action.
Keeping a proper look-out requires the OOW to ensure that all available means are used to obtain as much information as possible about the current traffic and navigation situation and then evaluate this information before taking action
Section III - Conduct of vessels in restricted visibility Rule 19
Conduct of vessels in 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.
(c) Every vessel shall have due regard to the prevailing circumstances and conditions of restricted visibility when complying with the Rules of Section I of this Part.
(d) A vessel which detects by radar alone the presence of another vessel shall determine if a close- quarters 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.
(e) Except where it has been determined that a risk of collision does not exist, every vessel which hears apparently forward of her beam the fog signal of another vessel, or which cannot avoid a close-quarters situation with another vessel forward of her beam, shall reduce her speed to the minimum at which she can be kept on her course. She shall if necessary take all her way off and in any event navigate with extreme caution until danger of collision is over.
Extracts from MGN 379
Extracts from MGN 379
To estimate risk of collision with another vessel the closest point of approach (CPA) must be established. Choice of appropriate avoiding action is facilitated by the knowledge of the other vessel’s track using the manual or automatic plotting methods. The accuracy of the plot, however obtained, depends upon accurate measurement of own ship’s track during the plotting interval. It is important to note that an inaccurate compass heading or speed input will reduce the accuracy of true vectors when using ARPA or ATA. This is particularly important with targets on near-reciprocal courses where a slight error in own-ship’s data may lead to a dangerous interpretation of the target vessel’s true track. The apparent precision of digital read-outs should be treated with caution.
If two radars are fitted (mandatory for ships of 3000 GT and over) it is good practice, especially in restricted visibility or in congested waters, for one to be designated for anti-collision work, while the other is used to assist navigation. If only one of the radars is fitted with ARPA then this should be the one used for anti-collision work and the other for navigation.
Pilotage BPG 22
What is ARPA?
Electronic Plotting Aid (EPA) EPA equipment enables electronic plotting of at least 10 targets, but without automatic tracking (Ships between 300 and 500 Gross Tonnage (GT)).
Automatic Tracking Aid (ATA) ATA equipment enables manual acquisition and automatic tracking and display of at least 10 targets (Ships over 500 GT). On ships of 3000 GT and over the second radar must also be equipped with an ATA, the two ATAs must be functionally independent of each other.
Automatic Radar Plotting Aid (ARPA) ARPA equipment provides for manual or automatic acquisition of targets and the automatic tracking and display of all relevant target information for at least 20 targets for anticollision decision making. It also enables trial manoeuvre to be executed (Ships of 10000 GT and over). The second radar must incorporate ATA if not ARPA.
Manual plotting equipment is no longer acceptable except for existing vessels still complying with SOLAS V/74.
Speed and heading inputs to the ARPA/ATA are satisfactory. Correct speed input, where provided by manual setting of the appropriate ARPA/ATA controls or by an external input, is vital for correct processing of ARPA/ATA data. Serious errors in output data can arise if heading and/or speed inputs to the ARPA/ATA are incorrect.
It should be noted that the observed and predicted relative motion of a target is unaffected by the choice of sea or ground stabilisation, allowing the same assessment of CPA and risk of collision. If switching between sea and ground stabilisation, the observer should be aware of the time required for the radar equipment to reprocess the stabilisation input data.
To estimate risk of collision with another vessel the closest point of approach (CPA) must be established. Choice of appropriate avoiding action is facilitated by the knowledge of the other vessel’s track using the manual or automatic plotting methods (see 3.2 above). The accuracy of the plot, however obtained, depends upon accurate measurement of own ship’s track during the plotting interval. It is important to note that an inaccurate compass heading or speed input will reduce the accuracy of true vectors when using ARPA or ATA. This is particularly important with targets on near-reciprocal courses where a slight error in own-ship’s data may lead to a dangerous interpretation of the target vessel’s true track. The apparent precision of digital read-outs should be treated with caution.
If two radars are fitted (mandatory for ships of 3000 GT and over) it is good practice, especially in restricted visibility or in congested waters, for one to be designated for anti-collision work, while the other is used to assist navigation. If only one of the radars is fitted with ARPA then this should be the one used for anti-collision work and the other for navigation.
