Eg if you're trying to shout over the wind.

Although from the same perspective the phonetic similarity "port" and "board" is probably not ideal, either.

In practice, and perhaps because of this, the pronunciation of "starboard" is heavy on the "star", with the latter part ending up more like "brd" or "b'd". Indeed, you can find the word written as "starb'd".

Clarity stems from brevity i.e. concise, carefully chosen words that leave no room for ambiguity.

Clarity absolutely does not stem from brevity. Brevity is good, but it pushes toward ambiguity, not clarity.

For example, consider spelling a word. The briefest approach is to say the names of letters. But these are similar, often differing only in one phoneme. E.g., P and B differentiating sounds are both bilabial plosives, differing only in whether they are voiced. But people for whom clarity is important will use something like the NATO Phonetic Alphabet. There, you'd say "papa" and "bravo". [1] It is much less brief, but much more clear.

[1] https://en.wikipedia.org/wiki/NATO_phonetic_alphabet

We might have a different view on what "brevity" means, then. The ITU/NATO alphabet you mentioned is a prime example of brevity. Other examples include those used by air traffic control and fighter pilots.