One of three in a boat somewhere off the Scottish mainland (6)

I believe the answer is:

harris

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'somewhere off the scottish mainland' is the definition.
(Harris is a Scottish island)

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for harris that I've seen before include "Joel Chandler --, creator of Brer Rabbit" , "Lewis with ------, Hebridean island" , "boating man" , "Hebridean area known for tweed" , "Hebridean area associated with tweed" .)

I've seen this clue in The Telegraph.

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