Boat in which to start off? (6)
I believe the answer is:
launch
I believe this clue is a double definition.
'boat' is the first definition.
(launch is a kind of boat)
'to start off?' is the second definition.
(thesaurus)
'in which' acts as a link.
(Other definitions for launch that I've seen before include "Power-driven boat" , "'Send into water or into space, say (6)'" , "Send off (a missile)" , "Establish" , "Put a new product on the market" .)