Right. Go into, say, maybe a large merchant ship (6)
I believe the answer is:
argosy
'a large merchant ship' is the definition.
(I've seen this in another clue)
'right go into say maybe' is the wordplay.
'right' becomes 'r' (common abbreviation).
'into' is an insertion indicator.
'maybe' indicates an anagram.
'r'+'go'='rgo'
'say' with letters rearranged gives 'asy'.
'rgo' put within 'asy' is 'ARGOSY'.
(Other definitions for argosy that I've seen before include "craft" , "A great fleet as Spain once had" , "Merchant ship (poet.)" , "Great merchant ship" , "One or more large merchant ships" .)