Large vessel’s cutter abandoning Plymouth at last (4)

I believe the answer is:

ewer

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'large vessel's' is the definition.
'ewer' can be an answer for 'vessel's' (ewer is a type of jug). I am unsure of the 'large' bit.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for ewer that I've seen before include "Oversized jug" , "Were (anag)" , "Water jug with wide mouth" , "Decorative pitcher" , "A type of jug" .)

I've seen this clue in The Times.

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