Well-known seagoing duck (5)
I believe the answer is:
drake
'duck' is the definition.
(I know that drake is a type of duck)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for drake that I've seen before include "Aquatic bird" , "it's used to fish" , "old sailor" , "Male bird" , "world traveller" .)