About to start sailing, upper-class guy to remove mooring lines (4-3)
I believe the answer is:
cast-off
'remove mooring lines' is the definition.
'cast off' can be an answer for 'remove' (casting off is a kind of removing). I am not sure about the 'mooring lines' bit.
'about to start sailing upper-class guy' is the wordplay.
'about' is an insertion indicator.
'start' suggests taking the first letters.
'upper' indicates anagramming the letters (I've seen 'up' mean this (letters get chucked up)).
'class guy' becomes 'caff' (I can't justify this - if you can you should believe this answer much more).
The initial letter of 'sailing' is 's'.
'to'+'s'='tos'
'tos' is an anagram of 'sto'.
'sto' placed inside 'caff' is 'CAST-OFF'.
'to' is the link.
Can you help me to learn more?
(Other definitions for cast-off that I've seen before include "Discard" , "Rejected item" , "Of ship, release from moorings" , "Finish knitting - go to sea" , "Abandoned garment" .)