Move stealthily from front of boat at length (5)
I believe the answer is:
prowl
'move stealthily' is the definition.
(synonyms)
'front of boat at length' is the wordplay.
'front of boat' becomes 'prow' (nautical term).
'at' is a charade indicator (letters next to each other).
'length' becomes 'l' (abbreviation in geometry).
'prow'+'l'='PROWL'
'from' acts as a link.
(Other definitions for prowl that I've seen before include "Move in a predatory manner" , "Move about with unlawful intentions" , "Nose around" , "Skulk" , "Walk menacingly" .)