The charterer may detain the vessel beyond the agreed laytime whilst loading or discharging and set this extra time against his payment of demurrage. There are, however, two qualifications to this rule. The vessel is not obliged to remain there indefinitely and any unreasonable delay may frustrate the purpose of the charter party. This means that once the vessel has been detained on demurrage for a reasonable time, the shipowner may be entitled to treat the contract as at an end (i.e. frustrated) and order the vessel away. Secondly, the owner may order his vessel away once the charterer has repudiated the contract. It will be held that the charter has repudiated the contract where it is obvious that there is no possibility of the contractual obligations being performed and that further delay will inevitably frustrate the purpose of the charter party. The basic principle when dealing with demurrage is that ‘once on demurrage, always on demurrage’. i.e. Demurrage is payable on all time lost after the expiration of the laytime including Sundays, holidays and any other excepted periods such as strikes. The length of time for which despatch money is payable depends, of course, on the terms of the charter party. Despatch money is frequently agreed on the basis, for example, of ‘all time saved’. This means actual time saved to the shipowner and includes both lay days and calendar days. Alternatively the agreement may me for despatch to be paid on all working time or all laytime saved. Additional information regarding laytime is contained in the Voyage Charterparty Laytime Interpretation Rules 1993 (Voylayrules 93) which have been prepared by BIMCO, FONASBA and other bodies.