Shoddy stuff aboard ship piles up (6)
I believe the answer is:
stacks
'piles up' is the definition.
(stack things up)
'shoddy stuff aboard ship' is the wordplay.
'shoddy stuff' becomes 'tack' (tack can mean shoddy or tasteless stuff).
'aboard' means one lot of letters goes inside another.
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'tack' going inside 'ss' is 'STACKS'.
(Other definitions for stacks that I've seen before include "Orderly piles or heaps" , "Large tall chimneys" , "Ricks" , "bags?" , "Orderly heaps as of hay" .)