Fling in direction of ship (4)
I believe the answer is:
toss
'fling' is the definition.
(I know that fling can be written as toss)
'in direction of ship' is the wordplay.
'in direction of' becomes 'to' (heading to).
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'to'+'ss'='TOSS'
(Other definitions for toss that I've seen before include "Raise a bit of money before opening" , "Raise a little money" , "Throw with a light motion" , "Throw lightly and casually" , "Fall from horse" .)