Affliction I found aboard vessel (4)
I believe the answer is:
pain
'affliction' is the definition.
(thesaurus)
'i found aboard vessel' is the wordplay.
'found aboard' indicates putting letters inside (inserted letters come on board).
'vessel' becomes 'pan' (vessel or container for cooking).
'i' put within 'pan' is 'PAIN'.
(Other definitions for pain that I've seen before include "Suffering of body or mind" , "Sensation of hurt" , "Suffering, distress" , "Physical discomfort" , "Tiresome figure" .)