Training in it out at sea (7)
I believe the answer is:
tuition
'training' is the definition.
(I've seen this before)
'in it out at sea' is the wordplay.
'at sea' indicates anagramming the letters.
'in'+'it'+'out'='initout'
'initout' with letters rearranged gives 'TUITION'.
(Other definitions for tuition that I've seen before include "Teaching, instruction" , "Training" , "(Individual) instruction" , "Schooling" , "Lessons" .)