What is the meaning of Phrase "if the circumstances of the case admit" in COLREGS? I really dont understand this sentence which has been used several times in COLREG.

I totally understand the confusion here and trust me, you are not alone. Imagine a cadet being subjected to these tough sentences. I believe if the circumstances of the case admit, there should be a simpler version of the rules of the road.

Ooops.. I used it too. But don't worry. I will simplify this.

Let us see the rules where this phrase is used

Now I am going to tell you to replace this phrase with two words. This will make it easier to understand these rules. These two words are "If possible".

Read these rules again by replacing the text in red with the words "if possible".

For example, now the text in rule 9 will become

Any vessel shall, if possible, avoid anchoring in narrow channel.

Now that we understand this phrase, it might give an impression to us that we can easily by-pass the rules. For example, it might look like, we can easily anchor in the narrow channel and say that it was not possible for us to avoid it.

But the onus to prove that it was really not possible, will be on the vessel that anchored. By default, it will be considered that it was possible to avoid anchoring.