A shipowner who charters his ship out on voyage charter may build in a provision in the freight for delay in berthing; this is easier for a tramp owner to do than it would be for a shipping line since most frequently the charter will apply to a single voyage whereas the freight rates of a shipping line are set for a much longer period and are, in any event, not intended to provide for temporary changes in circumstances. A common alternative for the tramp owner is to include a provision for demurrage.This is a penalty which cargo interests have to pay for taking longer than the time allowed for loading and/or discharging. In many charter-parties, any delay in reaching the berth, including delay caused by congestion, will count in the calculation of demurrage.