Navy tour in it at sea? Goodness! (9)
I believe the answer is:
nutrition
'goodness' is the definition.
'navy tour in it at sea?' is the wordplay.
'navy' becomes 'n' (common abbreviation eg in RN Royal Navy).
'at sea?' indicates anagramming the letters (I've seen 'at sea' mean this).
'tour'+'in'+'it'='tourinit'
'tourinit' anagrammed gives 'utrition'.
'n'+'utrition'='NUTRITION'
(Other definitions for nutrition that I've seen before include "form of sustenance" , "Food and drink, edibles" , "Act of nourishing" , "Food, its study" , "what's taken in?" .)