Incorrectly loaded ship - disaster! (4,4)
I believe the answer is:
dead loss
'disaster' is the definition.
(dead loss can mean a complete failure)
'incorrectly loaded ship' is the wordplay.
'incorrectly' is an anagram indicator (I've seen this in other clues).
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'loaded' is an anagram of 'deadlo'.
'deadlo'+'ss'='DEAD LOSS'
(Other definitions for dead loss that I've seen before include "Totally useless item" , "Unproductive person or thing" , "unprofitable" , "Unproductive person/thing" , "Useless person or thing - sounds moribund and profitless" .)