Cryptic crossword clue
What ship needs, in water, so she’s tight 13

The most common and most likely answer to this crossword clue is the 13 letter word SEAWORTHINESS

I've seen this crossword clue in The Sunday Telegraph
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Buddy explains!

The straight part
We know that "What ship needs" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what ship needs = seaworthiness.
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.

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