Rigid boat in difficulty (8)
I believe the answer is:
hardship
'difficulty' is the definition.
(hardship is a kind of difficulty)
'rigid boat' is the wordplay.
'rigid' becomes 'hard' (I've seen this before).
'boat' becomes 'ship' (I've seen this before).
'hard'+'ship'='HARDSHIP'
'in' is the link.
(Other definitions for hardship that I've seen before include "Lack of life's necessities, a tough time" , "State of misfortune or affliction" , "Severe difficulty or suffering" , "Difficulty, vicissitude" , "difficult to take" .)