Boat departed, males at sea (6,7)
I believe the answer is:
paddle steamer
'boat' is the definition.
(I know that Paddle steamer is a type of Steamboat)
'departed males at sea' is the wordplay.
'at sea' indicates anagramming the letters.
'departed'+'males'='departedmales'
'departedmales' anagrammed gives 'PADDLE-STEAMER'.
(Other definitions for paddle steamer that I've seen before include "Mississippi boat?" , "Type of ship" , "River boat, for example" , "Ship propelled by bladed wheels" , "vessel" .)