RN choose new vessel (8)
I believe the answer is:
schooner
'vessel' is the definition.
(type of ship)
'rn choose new' is the wordplay.
'new' indicates anagramming the letters.
'rn'+'choose'='rnchoose'
'rnchoose' with letters rearranged gives 'SCHOONER'.
(Other definitions for schooner that I've seen before include "In the main it is" , "wooden vessel" , "Sailing vessel used in former times" , "Type of glass" , "boat" .)