Hang about, departing at last in ocean-going vessel (6)
I believe the answer is:
linger
'hang about' is the definition.
(I've seen this before)
'departing at last in ocean-going vessel' is the wordplay.
'at last' suggests the final letters.
'in' means one lot of letters goes inside another.
'ocean-going vessel' becomes 'liner' (liner is a kind of vessel. I am not sure about the 'ocean-going' bit.).
The final letter of 'departing' is 'g'.
'g' put within 'liner' is 'LINGER'.
Can you help me to learn more?
(Other definitions for linger that I've seen before include "Remain behind" , "Delay departure" , "Procrastinate" , "Hang back awhile" , "Hang about, don't be in a hurry to go" .)