Berlin's rowers potentially follow unknown craft (5)
I believe the answer is:
yacht
'craft' is the definition.
(I know that yacht is a type of motorboat)
'berlin's rowers potentially follow unknown' is the wordplay.
'berlin's rowers potentially' becomes 'acht' ('eight' in German - eight can mean a rowing crew).
'follow' means one lot of letters go next to another.
'unknown' becomes 'y' (algebra).
'acht' after 'y' is 'YACHT'.
(Other definitions for yacht that I've seen before include "Cathy (anag.)" , "Light sailing vessel" , "Sailing boat" , "Pleasure craft" , "Sailing-boat" .)