The only theatre frequented by yachtsmen? (6)

I believe the answer is:

solent

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'the only theatre frequented by yachtsmen?' is the definition.
I can't judge whether this definition defines the answer.

'the only theatre' is the wordplay.
'the only' becomes 'sole' (I've seen this before).
'theatre' becomes 'NT' (National Theatre).
'sole'+'nt'='SOLENT'

Can you help me to learn more?

(Other definitions for solent that I've seen before include "sound" , "body of water" , "The ---, water N. of I. of Wight" , "Confine as a prisoner" , "Lets on to be an English waterway" .)

I've seen this clue in the Evening Standard.

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