This is because the response of a main engine to a change of throttle position is very slow when burning IFO. As this could affect the safety of the ship when an instantaneous response by the main engine is required, the fuel will be switched to MDO for an almost instantaneous response. With the diesel electric ship becoming more accepted, the configuration of engine types and propulsion systems will undoubtedly change. In the case described a better way of achieving a more instantaneous response will be done by putting more engines on or off line using electric switchgear just as power stations ashore adapt to changes in electricity demand. Most modern vessels will be ‘fully automated’, which is to say that the main engine can be directly controlled from the navigating bridge. When negotiating a vessel for timecharter employment, it is usual to describe the daily consumption at sea against each of a particular range of speeds at which the timecharterers may instruct the master to operate. It is also necessary to include the vessel’s port consumption when ‘idle’ – when the main engine is immobilised and the vessel is using auxiliary engines to provide heat, light and power but cargo gear is not being used. Port consumption ‘working’ allows for extra consumption needed to power a vessel’s cargo equipment – e.g. her cranes – and it is usual to additionally describe ‘working’ consumption against, say, every ‘8 hours working’ or ‘per 24 hours, all gear working’. Fuel oils are graded according to quality. Heavy fuel oil is usually described around 380 c/s (centistokes) but many modern ships are capable of burning 500-700 c/s fuels. Many Panamax and small vessels burn IFO (Intermediate Fuel Oil) 180 c/s in their main engine or even better quality – say – IFO 150 c/s. Certain operators also opt for higher quality gas oil rather than diesel oil in auxiliaries, and with smaller, short sea craft, it is common to run both main and auxiliary plant on marine diesel or gas oil.