Wild prank in sea, not a feature of yachting? (9)
I believe the answer is:
spinnaker
'feature of yachting?' is the definition.
(a spinnaker is a sail used on a yacht)
'wild prank in sea not a' is the wordplay.
'wild' indicates anagramming the letters.
'not' indicates named letters should be taken away.
'prank'+'in'+'sea'='prankinsea'
'prankinsea' with 'a' taken out is 'prnkinsea'.
'prnkinsea' anagrammed gives 'SPINNAKER'.
(Other definitions for spinnaker that I've seen before include "Large triangular sail at the front of a yacht" , "an expanse of cloth" , "one using the breeze" , "Lightweight sail" , "Large racing sail" .)