Descriptive of galley, a shade beneath surface of ocean (5)
I believe the answer is:
oared
'descriptive of galley' is the definition.
(having oars)
'a shade beneath surface of ocean' is the wordplay.
'shade' becomes 'red' (red is a colour or shade).
'beneath' says to put letters next to each other (in a down clue).
'surface of' suggests taking the first letters.
The first letter of 'ocean' is 'o'.
'a'+'red'='ared'
'ared' after 'o' is 'OARED'.
(Other definitions for oared that I've seen before include "ready for a row" , "As some boats flew" , "Propelled like a rowing boat" , "(Of a boat) provided with rowing blades" , "Like a rowing eight" .)