Vessel in good condition managed to support area (8)
I believe the answer is:
trimaran
'vessel' is the definition.
(trimaran is a kind of vessel)
'in good condition managed to support area' is the wordplay.
'in good condition' becomes 'trim' (I've seen this before).
'managed' becomes 'ran' (both can mean organised or was in charge of).
'to support' says to put letters next to each other (in a down clue, some letters hold up others).
'area' becomes 'a' (maths abbreviation).
'ran' after 'a' is 'aran'.
'trim'+'aran'='TRIMARAN'
(Other definitions for trimaran that I've seen before include "Sailing boat with 3 hulls" , "Three-hulled boat" , "Three-hulled vessel" , "Sailing boat with three hulls" , "Ocean vessel with three hulls side by side" .)