Seagoing vagabond (5)
I believe the answer is:
tramp
'vagabond' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for tramp that I've seen before include "one unlikely ever to have a mortgage!" , "Vagabond, hobo" , "Walk heavily like hobo" , "I usually walk" , "Merchant ship" .)