Q.Please define 'overtaking' in restricted visibility?

The biggest mistake I see navigators make in understanding the COLREGS is mixing the rules under different parts and sections of COLREGS.

If we understand that "Steering and sailing rules" are divided into three sections, it will make it much easier to understand COLREGS.

So what are these three sections?

In good visibility, the rules and actions are based upon three aspects of the target. These rules are

• Head on situation: when the target is right ahead or nearly right ahead.
• Crossing situation: When the target is crossing the vessel
• Overtaking Situation: When the target is overtaking own vessel or is being overtaken by own vessel 

But for restricted visibility, the rules and actions are based upon only two aspects. These are

• When the target is forward of the beam
• When the target is abeam or abaft the beam

Now when dealing with these rules, we must not mix this. If dealing with restricted visibility rules, we must only think of targets as either "forward of the beam" or "Abeam or abaft the beam".

So when talking about "Overtaking in restricted visibility", this needs to be addressed as "target abaft the beam" and not "overtaking. 

If you wish to know what action we are supposed to take in these situations, read these resources.

Infographic: Actions required in restricted visibility as per COLREG rule 19

8 COLREG rules every navigating officer must understand

I think overtaking has only one definition irrespective of visibility conditions

Although Rule 13 does not apply when navigating in an area of restricted visibility, it is widely accepted that its definition of overtaking is applicable when considering Rule 19 d (i).

Therefore all action taken whilst navigating in an area of restricted visibility must be in accordance with Rule 19. However, if by radar determination, you are approaching another vessel forward of your beam such that it falls within the definition of overtaking as per Rule 13, you can in fact over take her on her port side. The vessel being overtaken must also conform to Rule 19 and as such, cannot alter her course towards a vessel abaft her beam, thus shall alter her course to starboard if the circumstances of the case warrants action on her part. Remember, nobody has right of way whilst navigating in restricted visibility. 

It must be noted that Master's will increase their acceptable minimum CPA distances when navigating in restricted visibility and thus it is not expected to overtake another vessel at small CPA during such conditions. The vessel being overtaken must judge for themselves if a close quarters situation is developing, if yes, act as per rule 19 and not alter towards a vessel abeam.

Long story short: 

It is ok to overtake another vessel on her portside when navigating within an area of restricted visibility provided that your approach fits the definition of overtaking as per Rule 13.

All action must be in accordance with Rule 19, with the definition of overtaking only referenced from Rule 13, utilizing good radar information. 

I am glad that someone has finally noticed how equivocal, vague and confusing can be our precious rules. Rule 19 explicitly stipulates that it applies when vsls are not in sight of one another, thus Section 2 doesn't apply here. Rule 19 makes it crystal clear that there are only 2 sectors to consider i.e. fwd/abaft beams, period. Notwithstanding all above outlined, all of a sudden we come across the word 'OVERTAKING' right in the middle of the Rule 19 '' other than for a vessel being overtaken''. At first it seems completely inconsistent with what it states. Then you start to realize that you follow the rule only '' if a close quarters situation is developing and/or risk of collision exists '' .  But anyway... 

 On top of that, there is much more confusing point. It directs us '' 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. '' The part which doesn't leave in peace is ''which cannot avoid close quarter situation... shall reduce... '' The question suggests itself - why  this aspect is not outlined in Rule 14? What if we have head-on in sight of one another but I cannot alter to stbd for a variety of reasons?! Is it illegal to reduce speed or take all my way off in this case? Why is it introduced in Rule 19 and not touched upon in Rule 14? Why Rule 19 has this ambiguous word ''overtaking'' in the paragraph (d)(i). Why Rule 19 has no mention of AIS and VHF as a sources to determine the course of the vsl sounding the signal (in case we happen to have inoperable radar or no radar installed at all)?! On one hand I see why, on the other hand I don't get it at all. Thank you for reading, I appreciate your time.

Sir, when in RV, the sectors for overtaking will be the same as defined in Rule 13                ( 22.5deg abaft the beam) not abaft the beam. 

The reason is very simple. In a given set of rules there cannot be 2 different meanings to the same definition. If it has not been specifically defined in Rule 19 that Overtaking will be abaft the beam, then definition as per Rule 13 applies. 

This has been explained by Capt Anil Bhatia in his youtube channel. 

https://www.youtube.com/watch?v=3HgN0u4sCHw