Crew's leader I see heading for boat (4)
I believe the answer is:
five
'crew's' is the definition.
(thesaurus)
'leader i see heading for boat' is the wordplay.
'leader' becomes 'f' (I have seen 'German leader ' mean 'f' so perhaps 'leader' could also mean 'f').
'see' becomes 'v' (short for 'vide', Latin meaning 'see elsewhere').
'heading for' says to put letters next to each other.
'boat' becomes 'e'.
'f'+'i'+'v'+'e'='FIVE'
(Other definitions for five that I've seen before include "Cardinal" , "Number of towns Arnold Bennett's Anna is associated with" , "Fourth part of score" , "famous group" , "V as a numeral" .)