Place leading navigator inside boat (4)
I believe the answer is:
punt
'boat' is the definition.
(thesaurus)
'place leading navigator inside' is the wordplay.
'place' becomes 'put' ('put' can be a synonym of 'place'**).
'leading' suggests taking the first letters.
'inside' is an insertion indicator.
The first letter of 'navigator' is 'n'.
'put' enclosing 'n' is 'PUNT'.
(Other definitions for punt that I've seen before include "gambling" , "taken by a better" , "Bet (in old Irish money?)" , "Former currency of Ireland" , "risky affair" .)