Crossword Genius

Shift at sea with Coastguard — be in good shape (3,2,1,8,3)

Ross

I believe the answer is:

fit as a butchers dog

Here is my best explanation:

'shift at sea with coastguard be in good shape' is the definition.
I know nothing about this answer so I cannot judge whether this works.

'shift at sea with coastguard be' is the wordplay.
'at sea with' is an anagram indicator.
'coastguard'+'be'='coastguardbe'
'shift' mixed up with 'coastguardbe' gives 'FIT AS A BUTCHERS DOG'.