Right boards used to be swinging in frigate, say (7)
I believe the answer is:
warship
'frigate say' is the definition.
(I know that destroyer escort is a type of warship)
'right boards used to be swinging' is the wordplay.
'right' becomes 'r' (abbreviation).
'boards' means one lot of letters goes inside another.
'used to be' becomes 'was' (eg 'he was...' means 'he used to be...').
'swinging' becomes 'hip' (I've seen this before).
'r' going inside 'was' is 'wars'.
'wars'+'hip'='WARSHIP'
'in' is the link.
(Other definitions for warship that I've seen before include "frigate perhaps" , "Fighting vessel" , "It's armed at sea" , "Eg, destroyer, cruiser" , "Navy asset" .)