Spanking vessels? (6)
I believe the answer is:
smacks
'vessels?' is the definition.
(smack is a kind of vessel)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for smacks that I've seen before include "Slaps the fishing boats?" , "Strikes with the hand" , "Loud slaps for fishing vessels" , "Slaps; flavours; boats" , "Punishes" .)