Opening secured by the German fishing-boat (7)
I believe the answer is:
drifter
'fishing-boat' is the definition.
(I've seen this before)
'opening secured by the german' is the wordplay.
'opening' becomes 'rift' (rift is a kind of opening).
'secured by' is an insertion indicator (I've seen this in other clues).
'the german' becomes 'der' ('the' in German).
'rift' put inside 'der' is 'DRIFTER'.
(Other definitions for drifter that I've seen before include "Itinerant type" , "tramp, perhaps" , "Wanderer; fishing vessel" , "Vagabond" , "fellow lacking direction" .)