Given that the vessel had been trawling round (9)
I believe the answer is:
furnished
'given' is the definition.
(furnishing is a kind of giving)
'the vessel had been trawling round' is the wordplay.
I cannot really see how this works, but
'vessel' could be 'urn' (urn is a type of container) and 'urn' is located in the answer.
'had' could be 'd' (in contractions e.g. 'I'd', 'you'd' etc) and 'd' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
'that' is the link.
Can you help me to learn more?
(Other definitions for furnished that I've seen before include "Provided, supplied" , "Equipped with tables,chairs etc" .)