I object; the vessel is in an untidy state (4)
I believe the answer is:
mess
'an untidy state' is the definition.
(state of being untidy)
'i object the vessel' is the wordplay.
'i object' becomes 'me' ().
'the vessel' becomes 'SS' (prefix in ship names eg SS Great Britain).
'me'+'ss'='MESS'
'is in' acts as a link.
(Other definitions for mess that I've seen before include "dirty and unpleasant" , "Dirty or untidy state" , "Disagreeable mixture" , "Disarray" , "Canteen - litter" .)