Short tons swindle cargo boat (5)
I believe the answer is:
tramp
'cargo boat' is the definition.
(I've seen this before)
'short tons swindle' is the wordplay.
'short tons' becomes 't' ('short' indicates a short form).
'swindle' becomes 'ramp' (I've seen this before).
't'+'ramp'='TRAMP'
(Other definitions for tramp that I've seen before include "Vagrant, drifter" , "Walk heavily - steamer" , "cargo boat" , "sometimes harboured?" , "I might hitch a lift" .)