It's hard getting into grimy boat (6)
I believe the answer is:
dinghy
'boat' is the definition.
(dinghy is a kind of boat)
'it's hard getting into grimy' is the wordplay.
'it's hard' becomes 'h'.
'getting into' means one lot of letters goes inside another.
'grimy' becomes 'dingy' ('dingy' can be a synonym of 'grimy').
'h' put inside 'dingy' is 'DINGHY'.
(Other definitions for dinghy that I've seen before include "Small boat, may be a rubber inflatable" , "Light rowing boat" , "Small boat propelled with oars" , "Small open boat, may be inflatable" , "Small open boat, maybe a rubber inflatable" .)