Getting cold in rough sea, hobby surfers from the 1960s (5,4)

I believe the answer is:

beach boys

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'getting cold' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.

'rough sea hobby surfers from the 1960s' is the wordplay.
'rough sea hobby surfers' becomes 'beachboy' (I can't justify this - if you can you should believe this answer much more).
'from' says to put letters next to each other.
'the b9b0s' becomes 's'.
'beachboy'+'s'='BEACH BOYS'

'in' is the link.

Can you help me to learn more?

I've seen this clue in The Telegraph.

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