Maneuvering the Sally Maersk

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systems digital sea charts or the way point position can be entered manually byreference to the master's spreadsheet version. On the Sally Mærsk the latter is thecase. The reason is that the vessel is in line service and thus calls on a fixed set ofharbors during a round trip. This normally means that only moderate changes need tobe made to the passage plans in-between round trips—and the standard passage planfor a specific round trip can thus be reused.In terms of automation the track plan is at the heart of the voyage managementsystem. In theory the coupling between track plan data and tuning parameters, sensorinput, radar targets, etc. may lead to the conclusion that the voyage managementsystem is capable of sailing the ship from port A to port B. However, reality tells adifferent story.Even though the voyage management system is far more sophisticated than theauto pilot both systems are—at the end of the day—automatic track followingdevices. The voyage management system—in contrast to the auto pilot—is capable offollowing a series of subsequent course segments; yet non of the systems have anycapabilities in regard to automating traffic issues: traffic is represented within thevoyage management system for the purpose of visual presentation but the system hasno model for the actual handling of traffic. As a consequence, track following isperformed manually in restricted waters with dense traffic. Automatic trackfollowing—performed by means of the auto pilot or the voyage management systemis only engaged in open water with ample space and little traffic.The fully automatic track following performed by the voyage management systemis refered to as the NAV MODE. But most often the voyage management system isrunning in the so called ADVISORY MODE. The two modes are identical with respect tothe calculations performed by the voyage management system. However, inADVISORY MODE the calculations are only displayed on the monitor—while the link tothe lower levels of the steering and propulsion control systems remains blocked. Inother words, the advise given by the voyage management system will only take effectif they are implemented by the navigating officer. The actual information provided bythe voyage management system will be discussed in more detail in the report dealingwith navigation issues.Maneuvering characteristicsThe rudder fitted on the Sally Mærsk is a conventional spade-type rudder—a passivedevice in the sense that it functions by guiding forces that are not the product of therudder itself. The rudder only functions if there is a certain magnitude of waterpressure on the rudder blade.Intuitively, one may assume that the rudder achieves its guiding effect on themovements of the vessel by pushing the water hitting the rudder blade to starboard orport. But in fact, the push only accounts for one third of the rudder effect. Theremaining comes from the vacuum and consequent suction effect created on the backside of the rudder blade—the side of the rudder facing away from the water pressure.In the case of the Sally Mærsk, the rudder demands a water pressure equivalent topressure available when the vessel is moving ahead at speeds of three knots or greaterspeeds. Below this magnitude of water pressure, the rudder has no significant effect on themaneuverability of the vessel.12
Figure 22: Turning circle for Sally Mærsk at 94 RPM in the loaded condition.The above figure shows the maneuvering characteristics of the Sally Mærsk duringa 360° turn as measured during test runs. Measurements were performed during tworuns at 94 RPM with the rudder hard a port and a starboard respectively. During thestarboard turn, the vessel advances 750 m. while transferring 800 m. The entire 360°starboard maneuver took 215 sec. while the 90° turn a starboard took 100 sec. Thebelow figure illustrates the test results for a 360° turn performed at 50 RPM.Figure 23: Turning circle for the Sally Mærsk at 50 RPM in the loaded condition.As can be seen from the two figures, the vessel uses less time but covers moreground when turning at greater speeds.PropulsionIn the following we will look at the controllable forces driving the vessel through thewater. We will consider the functioning and use of the main engine propulsion systemand the thrusters, and we will present the data illustrating the actual maneuveringcapabilities of the Sally Mærsk. We will start by introducing the main enginepropulsion system.AccelerationThe Sally Mærsk is fitted with one Mitsui-B&W 12k 90 MC two-stroke, singleacting, turbo-charged crosshead marine diesel engine with direct reversing—capable13
Page 1 and 2: Maneuvering the Sally MaerskM O R T
Page 3 and 4: MANEUVERING THE SALLY MÆRSKIntrodu
Page 5 and 6: Figure 2. Helm standThe rudder move
Page 7 and 8: Auto PilotThe auto pilot is capable
Page 9 and 10: identical function but the limitati
Page 11: Passage plan: ROTTERDAM DEPARTUREWP
Page 15 and 16: Figure 25. Main engine telegraph.Ba
Page 17 and 18: Figure 28: The crash astern test.Fi
Page 19: Figure 31: Thruster controls.The th

Maneuvering the Sally Maersk

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