Presumptive taxation for non-resident shipping treats freight and related charges as deemed income with return, assessment and port clearance obligations. A fixed presumptive computation treats freight and related receipts of non-resident shipping operators (other than cruise shipping) as deemed income, including demurrage and handling charges. Current and carried depreciation of other businesses cannot be set off; other business losses may be. The ship's master must file a return of amounts paid or payable before departure (or an authorised person within thirty days), the Assessing Officer assesses tax at rates for foreign companies, and port clearance is withheld until tax is paid or satisfactory arrangements are made.