‘I would determine if a risk of collision exists’ is a phrase you will remember from COLREGS 1: Wording
But how do we go about determining if risk of collision exists? This is where Rule 7 - Risk of Collision comes into play.
Relevant documents and M-Notices: MSN 1781, MGN 324, MGN 369, MGN 379
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 such risk shall be deemed to exist.
‘All available means appropriate to the prevailing circumstances’
This harks back to some extent to Rule 5 - Lookout : let’s remind ourselves of that before going forward. Have a quick read of the relevant part of COLREGS 3.
All available means include:
Sight
Hearing
Compass repeater
Radar and ARPA
This is a bit different than the ‘all available means’ used to keep a watch as described in Rule 5. The reason for this is that, while Rule 5 uses the phrase ‘a full appraisal of the situation and of the risk of collision’, Rule 7 uses ‘to determine if risk of collision exists’. Some means are appropriate for making an appraisal of the situation and improving situational awareness - AIS and VHF radio, for example - but cannot be used to determine risk of collision.
From MGN 324, regarding AIS:
This should be treated with extreme caution and only used for enhancing situation awareness and not for collision avoidance decision-making.
AIS target data will only be based on the target vessels’ course and speed over ground whilst for COLREG compliance such data must be based on the vessels’ course and speed through the water.
Collision avoidance must be carried out in strict compliance with the COLREG. There is no provision in the COLREG for use of AIS information, therefore, decisions should be taken based primarily on systematic visual and/or radar observations.
From MGN 369:
The use of AIS for early identification of targets maybe useful to the OOW but the information provided should not form the basis of determining if a risk of collision exists.
‘appropriate to the prevailing circumstances and conditions’
This phrase frees the OOW up to focus on the most suitable means in any given set of circumstances. In very thick fog, while they naturally need to keep a look out by all available means, the primary means of determining if risk of collision exists will be radar and sound. In good visibility it will generally be sight (including compass bearings), supplemented by radar.
‘If in doubt, such risk shall be deemed to exist’
If you’re not sure if risk of collision exists - perhaps the bearing is changing but you can’t decide if it’s an appreciable change or not, or the CPA keeps changing - then assume that risk of collision does exist. This isn’t the only time that the rules ask you to assume that a situation exists if in doubt; Rules 13 and 14 have similar provisions. Get used to the idea that, if you’re in doubt, assume that such a situation exists and take action as appropriate.
Rule 7, part b:
(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.
If you have radar, you should be using it. An operational radar means a radar set without known defects. Remember that Rule 7 is part of section I - Conduct of vessels in any conditions of visibility. Radar isn’t just for restricted visibility.
Long range scanning gives early warning of the presence of a vessel or object. Radar plotting or equivalent systematic observation means either manual plotting or use of ARPA. From MGN 369:
The OOW should make systematic observations of targets to determine if a risk of collision exists, noting that ARPA only produces systematic observations of targets that have been acquired. It is therefore important that the OOW ensures that targets are either acquired within ARPA or another method used of obtaining systematic observations of targets.