Galley: new timer about to be installed (7)
I believe the answer is:
trireme
'galley' is the definition.
(trireme is a kind of galley)
'new timer about to be installed' is the wordplay.
'new' indicates an anagram.
'about' becomes 're' (common abbreviation for 'with reference to').
'to be installed' is an insertion indicator.
'timer' with letters rearranged gives 'trime'.
'trime' placed around 're' is 'TRIREME'.
(Other definitions for trireme that I've seen before include "Ancient rowed ship" , "Oar-driven battleship of classical times" , "Roman/Greek galley" , "Ancient Greek or Roman war galley" , "Ancient vessel with three banks of oars on each side" .)