The main narrow channel for the voyage (3,7)

I believe the answer is:

sea passage

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'the voyage' is the definition.
Both the answer and definition are singular nouns.
Maybe they are linked in a way I don't understand?

'the main narrow channel' is the wordplay.
'the main' becomes 'sea' (the main is an old name for the sea).
'narrow channel' becomes 'passage' (I've seen this before. I am not sure about the 'narrow' bit.).
'sea'+'passage'='SEA PASSAGE'

'for' is the link.

Can you help me to learn more?

(Another definition for sea passage that I've seen is " main journey".)

I've seen this clue in The Irish News.

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