The most common and most likely answer to this crossword clue is the 12 letter word SUPERCARGOES
I've seen this crossword clue in The Guardian
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Buddy explains!
The straight part
We know that "Officers afloat, overseeing/Officers afloat/, overseeing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case officers afloat, overseeing/officers afloat/, overseeing = supercargoes.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
Crossword Answer definitions
SUPERCARGOES noun- An officer on board a merchant ship who has charge of the cargo and its turnover (or the senior of two if one has two, the other being the subcargo; usually historical, since nowadays a person with such a job would remain on shore).