Old boy brought aboard ship cries (4)
I believe the answer is:
sobs
'cries' is the definition.
(sobbing is a kind of crying)
'old boy brought aboard ship' is the wordplay.
'old boy' becomes 'OB' (abbreviation for a private school 'old boy').
'brought aboard' indicates putting letters inside (inserted letters come inside or on board).
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'ob' inserted inside 'ss' is 'SOBS'.
(Other definitions for sobs that I've seen before include "convulsions" , "Cries loudly" , "cries uncontrollably" , "showing distress" , "Weeps heavily (4)" .)