Can volunteers ruin a concealed vessel? (9)
I believe the answer is:
catamaran
'vessel?' is the definition.
(catamaran is a kind of vessel)
'can volunteers ruin a concealed' is the wordplay.
'volunteers' becomes 'TA' (abbreviation for Territorial Army).
'ruin' becomes 'mar' (I've seen this before).
'concealed' indicates putting letters inside.
'ta'+'mar'+'a'='tamara'
'can' going around 'tamara' is 'CATAMARAN'.
(Other definitions for catamaran that I've seen before include "Twin-hulled sailing boat" , "raft of logs" , "Boat with twin, parallel hulls" , "One vessel" , "Twin-hulled vessel" .)