People who cast nets, say, hang around on board ship (8)

'people who cast nets say' is the definition.
(a net might be slung out into the sea)

'hang around on board ship' is the wordplay.
'hang around' becomes 'linger' (linger can mean to wait or hang around).
'on board' means one lot of letters goes inside another (inserted letters are taken on board).
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'linger' going into 'ss' is 'SLINGERS'.