Troublemaker on a ship, sailor the French blocked (10)
I believe the answer is:
impassable
'blocked' is the definition.
(I've seen this before)
'troublemaker on a ship sailor the french' is the wordplay.
'troublemaker' becomes 'imp' (I've seen this before).
'on' means one lot of letters go next to another.
'ship' becomes 'ss'.
'sailor' becomes 'ab' (abbreviation for able seaman).
'the french' becomes 'le' (**).
'imp'+'a'+'ss'+'ab'+'le'='IMPASSABLE'
(Other definitions for impassable that I've seen before include "Blocked to travel" , "preventing progress" , "won't be crossed" .)