Sea passages (8)

I believe the answer is:

gangways

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'sea passages' is the definition.
'gangways' can be an answer for 'passages' (I've seen this before). I am not sure about the 'sea' bit.

'sea passages' is the wordplay.
'sea' becomes 'gang' (I can't explain this - if you can you should believe this answer much more).
'passages' becomes 'ways' (I've seen this in another clue).
'gang'+'ways'='GANGWAYS'

Can you help me to learn more?

(Other definitions for gangways that I've seen before include "Passages going on board" , "Movable bridges for boarding ships" .)

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

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