Ship's platform isn't gone round by cleaner (7)
I believe the answer is:
maintop
'ship's platform' is the definition.
'maintop' can be an answer for 'platform' (I've seen this before). I'm unsure of the 'ship's' bit.
'isn't gone round by cleaner' is the wordplay.
'isn't' becomes 'aint' (non-standard version of 'isn't').
'gone round by' means one lot of letters goes inside another.
'cleaner' becomes 'mop' (something which 'cleans').
'aint' going inside 'mop' is 'MAINTOP'.
Can you help me to learn more?
(Other definitions for maintop that I've seen before include "Platform on a mast of a square-rigger - I'm on tap (anag)" , "Platform at the pinnacle of a mast" , "Superior position on board" , "one such at sea" , "Part of ship" .)