Maneuvering the Sally Maersk

of producing 74640 BHP at 94 RPM. In short: 12 cylinders, 74640 horse power and acruise speed of 24 knots.A direct reversing engine like the one fitted on the Sally Mærsk has no clutch andno gear: one revolution of the engine equals one revolution of the main propeller.Accelerations are thus achieved by increasing the amount of fuel being pumped intothe cylinders. While en route (also referred to as 'sea passage') only very few andminor changes are made to the RPM of the main engine. However, well in timebefore a harbor approach, the operational mode of the main engine will be switchedto 'maneuvering' allowing for rapid and frequent changes to the production ofpropulsion. The below table lists the approximate correlation between RPM andspeed.RPM and SpeedEngine order RPM Speedloaded conditionSpeedballast condition85% MCR AHEAD 94 23.6 knots 24.6 knotsFULL AHEAD 65 16.7 knots 17.3 knotsHALF AHEAD 50 12.8 knots 13.6 knotsSLOW AHEAD 35 8.9 knots 9.6 knotsDEAD SLOW AHEAD 25 6.3 knots 6.9 knotsFigure 24. RPM and speed.The number of revolutions per minute (RPM) of the main engine is controlleddirectly from the bridge. Three operational modes are available:1. Automatic speed control via the voyage management system2. Automatic speed control via the auto pilot3. Automatic speed control via the load program4. Manual speed control via the engine telegraph5. Manual speed control via the emergency engine telegraph6. Manual speed control via telephone connection to an engineer in the enginecontrol roomThe voyage management system and the auto pilot represent the two highest levelsin the speed control system (which runs on top of the engine control system). Boththe voyage management system and the auto pilot are capable of controlling thevessels speed (via altering the RPM of the main engine) but in practice speed isalways controlled via hands on control of the main engine telegraph.Accelerations up to speeds of about six knots are performed fully manually, whilethe remaining acceleration up to cruise speed is handled automatically by the socalled'load program'. In case the RPM of the main engine is increased at a too fastrate, the risk of inflicting serious thermal damage to the engine is imminent.14