Sailor with ornament was obliged to entertain head of Navy (8)
I believe the answer is:
deckhand
'sailor' is the definition.
(deckhand is a kind of sailor)
'ornament was obliged to entertain head of navy' is the wordplay.
'ornament' becomes 'deck' (decking is a kind of ornamenting**).
'was obliged' becomes 'had' (to have to do something is to be obliged to do it).
'to entertain' indicates putting letters inside.
'head of' says to take the initial letters.
The first letter of 'navy' is 'n'.
'had' placed around 'n' is 'hand'.
'deck'+'hand'='DECKHAND'
'with' is the link.
(Other definitions for deckhand that I've seen before include "crew member" , "seaman" , "Ship worker" , "one employed on board?" .)