Maneuvering the Sally Maersk

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stop engine, etc.). When a button is pushed on the bridge (indicating a command) thebutton will start blinking on the bridge and in the engine control room. The engineerin the engine control room confirms the command by pressing the button: theblinking stops and the now constantly lit button indicates the most speed command.The load program display is shown at the right hand side of figure 24. The twonumerical readings represent the desired and the actual RPM of the main engine. Thebuttons at the bottom of the display for fine tuning the RPM and for overriding theload program (the latter used in cases of emergency only).In terms of acceleration it is important to notice that it takes more than horsepower to get the vessel moving: it also takes water under the keel, and preferably lotsof it. Forceful accelerations in shallow waters will lead to increased turbulence at thepropeller, a higher stern wave, bad fuel economy, and only limited acceleration. As arule of thumb the vessel needs a water depth below the keel equaling twice its draughtin order to accelerate freely.DecelerationThe massive inertia inherent to the vessel becomes strikingly clear should the needfor a crash astern maneuver (emergency braking) occur. The below table lists the timeand distance needed to arrest the ahead movement of the vessel at various speedsduring loaded and ballast condition.Time and distance to stopLoaded condition Ballast conditionTime Distance Time Distance85% MCR ahead 960 sec 6100 m. 540 sec. 3240 m.HALF ahead 410 sec. 1600 m. 260 sec. 1000 m.Figure 27: Time and distance to stop the vessel.The long stopping distances are not solely the product of inertia, but can also beatributed to the de facto powers of braking available given the nature of the directreversing engine.The first step in reducing the speed of the vessel is to cut off the fuel supply to themain engine. This is done by setting the main engine telegraph in the 'Stop' position.Hereafter no power will be produced, yet the pistons will still move as a consequenceof the water pressure on the propeller: The rotations of the propeller will beforwarded to the pistons via the drive shaft and the connecting rods. Active brakingwould take to stop and reverse the pistons. However, the propeller has a diameter of10 meters, and when travelling at full speed, the forces produced by the water turningthe propeller simply prevent active braking. That is, active braking at full speed ispossible (via the engine telegraph) but at the risk of severely damaging or tearingloose the main propulsion plant. Therefore, it is not recommended to go astern untilthe vessel is at a speed below six knots.Between full speed and six knots, the only safe way of reducing the vessel’s speedactively is by means of the rudder. The rudder blade has a surface area of more than100 m2, and by putting the rudder at the maximum angle (35°) to either starboard orport, a noticeable braking effect is achieved. When the vessel starts turning, therudder is moved from hard a port to hard a starboard or vice versa.16
Figure 28: The crash astern test.Finally, the crew can decide to let go the anchors in order to arrest the vessel. Inpractice, however, this is only feasible at low speed—or else, at best, they risk rippingthe anchor chain or tearing the winches clean off the mooring deck! Yet, if this iswhat it takes to avoid a collision or grounding, these types of damages can certainlybe considered minute.Uneventful deceleration is performed over a relatively long time span. Most oftenthe deceleration from full to maneuvering speed (six knots) is handled automaticallyby the load program that cuts the engine’s revolutions at a rate of two RPM perminute. Decelerations from six knots and down are performed manually by means ofthe main engine telegraph (but preferably at a moderate rate). The load program canbe overridden in cases of emergency.ThrustersThe Sally Mærsk is fitted with three thrusters. One Brunvol thruster with a maximumlateral thrust of 30 t. at the bow and two 15 t. thrusters at the stern. The bow thrusteris fitted 22.23 m. abaft the front of the bulbous bow at a height of 4.69 m. above thekeel. The stern thrusters are fitted 28.58 m. and 33.42 m. forward of the transom at aheight of 2.66 m. above the keel.17
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 and 12: Passage plan: ROTTERDAM DEPARTUREWP
Page 13 and 14: Figure 22: Turning circle for Sally
Page 15: Figure 25. Main engine telegraph.Ba
Page 19: Figure 31: Thruster controls.The th

Maneuvering the Sally Maersk

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