The vessels will be refitted in the end of August (4)

I believe the answer is:

tugs

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'the vessels' is the definition.
(tug is a kind of vessel)

I cannot understand how the rest of the clue works.

(Other definitions for tugs that I've seen before include "Yanks" , "Tows" , "Pulls in a jerking manner" , "Pulls hard" .)

I've seen this clue in the Evening Standard.

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