A great stop for sailors (5)

I believe the answer is:

avast

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

'stop for sailors' is the definition.
'avast' can be an answer for 'stop' (I've seen this before). I am not certain of the 'for sailors' bit.

'a great' is the wordplay.
'great' becomes 'vast' (I've seen this in another clue).
'a'+'vast'='AVAST'

Can you help me to learn more?

(Other definitions for avast that I've seen before include "eleven [CEASE] at sea" , "Stop at sea" , "Stop on board" , "order for tar" , ""stop" signal" .)

I've seen this clue in The Guardian, The Globe and Mail and The Telegraph.

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