1. The vessel which is required not to impede the passage of the other shall take early avoiding action to prevent a risk of collision from developing.
2. If, for any reason she does not do so and a risk of collision exists, the vessel whose passage is not to be impeded remains fully obliged to take avoiding action in accordance with steering and sailing rules, specifically Rule 15(crossing).
3. It is for this reason that the vessel which is required not to impede is instructed by this rule to have due consideration of the possible avoiding action that may be taken by the vessel which is not to be impeded.

To demystify this, a classic example of a crossing situation between a power driven vessel and a vessel constrained by her draught is taken. The PDV has the CBD vessel on her port bow.

As per rule 8(f)(i) the PDV shall take early action to prevent risk of collision from building up.

The options for her action are:

1. Alter course to starboard and turn around and pass astern of the CBD vessel.
2. Reduce speed to allow CBD vessel to pass ahead.
3. Alter course to port and pass astern of the CBD.

Option No. 3 was prohibited by this Examiner as 8(f)(iii) still obliges the CBD vessel to keep out of the way if a risk of collision develops. Rule 8(f)(ii) reminds the PDV to have due regard to 8(f)(iii). In short, if a risk of collision exists (within close TCPA), then rule 15 is in effect.

There is a clear distinction between ‘shall keep out of the way of’ and ‘shall avoid impeding the passage of’. While the first edict is about right of way, the second is about simple road courtesy. I do not see anything confusing here. Take the traffic rules on the highways.

While at a crossroad (in India), the car on your right side has the right of way and you let it pass. However if you see a large lumbering tanker truck on your left, out of consideration for its sluggishness (not to mention your own safety), you slow down to a crawl and let it pass. I guess it's the same with ships.