Travelling ocean in boat (5)
I believe the answer is:
canoe
'boat' is the definition.
(I know that canoe is a kind of boat)
'travelling ocean' is the wordplay.
'travelling' is an anagram indicator.
'ocean' with letters rearranged gives 'CANOE'.
'in' acts as a link.
(Other definitions for canoe that I've seen before include "Kayak, for instance" , "Ocean (anag)" , "Boat one paddles" , "Primitive boat" , "Small boat for paddling" .)