Sailors, say, unhappy about porridge? (9)

I believe the answer is:

bluecoats

I'm a little stuck... Click here to teach me more about this clue!

'sailors' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.

'unhappy about porridge?' is the wordplay.
'unhappy' becomes 'blue' (blue can mean sad or miserable).
'about porridge?' becomes 'coats' (I can't justify this - if you can you should believe this answer much more).
'blue'+'coats'='BLUECOATS'

'say' acts as a link.

Can you help me to learn more?

I've seen this clue in The Independent.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.