In the ocean ten navigators needed aerial (7)
I believe the answer is:
antenna
'aerial' is the definition.
('antenna' can be a synonym of 'aerial')
'in the ocean ten navigators' is the wordplay.
'in' indicates the answer is hidden within the clue.
'ANTENNA' can be found hidden inside 'the ocean ten navigators'.
'needed' is the link.
(Other definitions for antenna that I've seen before include "What detects signals" , "Insect's feeler" , "Feeling part" , "could send out a message" , "Transmitting aerial" .)