Horse saves one fellow at sea (8)

I believe the answer is:

maritime

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'at sea' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for maritime that I've seen before include "Relating to the sea" , "Of seafaring or shipping" , "Naval" , "Found near the sea" , "Coastal" .)

I've seen this clue in The Sun.

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