The most common and most likely answer to this crossword clue is the 8 letter word SHIPWORM
I've seen this crossword clue in The Times
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The straight part
We know that "Prow’s damaged with him" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case prow’s damaged with him = shipworm.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.
What does SHIPWORM mean?
SHIPWORM noun- Any of several wormlike marine mollusks (not true worms) of the family Teredinidae, that bore through the wooden hulls of ships and other woody material immersed in salt water.