Azipod propulsion systems - Martin's Marine Engineering Page

forward-mounted propellers, "pull" their vessels). Thepositioning of the Azipod and the speed of their motorsare determined by officers on the bridge.End-View of POD(3) Strut ModuleStrut module acts as a connective element in CompactAzipod structure. Control cables, piping and powersupply bus bars for propulsion motor are located insidethe one -piece cast called strut module.(4) Power Transmission and Steering ModuleModuleAzipod is a Podded propulsion system, azimuthingthrough 360 degrees. Power transmission and steeringmodule consists of local control and equipment box,cable drum (slipping unit as an option), steering motorswith gearboxes and assembly block. This model islocated inside the hull of ship. The shaft can be rotatedto any position in 360 degrees. The angular position ofrotation can change the direction of the ship'smovement or keep it sailing straight ahead. Thus, shipswith Azipods are steered without a rudder, similarly assmall boats use an outboard motor for power andsteering (but with their rear-mounted propellers,outboards "push" their vessels, while Azipod, withCrossectional View of AZIPODDesign Features:The design of Compact Azipod includes features thatmake system a reliable and effective for DYNAMICPOSITIONING operation. Power transmission insteering module is installed in the ship hull in theconvenient phase of ship construction. Pre-mountedstrut and motor modules are delivered and installed andconnected to the power and steering module only justbefore launching of the ship. Reliability, availabilityand maintainability are important factors during thedesign phase. Possibility to take full power withreversed RPM, precise azimuthing control, Azimuthingspeed, Possibility to tilt the unit are the few essentialthings to be borne in mind during the design.The Azipod-propelled ship achievesgreater fuel efficiency by the use of the latest materials,many stronger and lighter in weight than were used inconstruction in earlier designs.Electric Propulsion:Functionally, the propulsion drive can be divided intofollowing parts:(I) Supply transformer(II) Propulsion motor(III) Frequency converter.This document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net

The advantagesThe reliability and effectiveness of Azipod propulsionhas been proven over the last decade in the toughestocean-going ship applications: Arctic tankers and icebreakers. In those non-passenger-carrying vessels,propulsion was provided by only one Azipod, where ascruise ships may have two for additionalmaneuverability and redundancy.Azipod propulsion enhances the merits of electricpropulsion in a number of ways:Various Electrical InstallationsIn an AC drive, a frequency converter is used to controlthe speed and torque of electric motor housed in theazipod unit. The speed of the AC electric motor can becontrolled by varying the voltage and frequency of itssupply. A frequency converter works by changing theconstant frequency mains electrical supply into avariable frequency output. The frequency converterdrive provides step less control of three-phase ACcurrents from zero to maximum output frequency,corresponding to a desired shaft speed both ahead andastern directions. High torque is available at all speeds.Controller hardware and software are designed for safeoperation in all conditions, as well as for high dynamicperformance. Optional control parameters are flexiblyprogrammable according to special requirements.1 Superior maneuverability and dynamicperformance are advantages which are notprovided by the earlier system. Excellentreversing capability and steering during asternnavigation, and enhanced crash stopperformance are the important features. Testson arctic tankers converted from conventionaldrive to unconventional one shows a 46%reduction in crash stop distance over thepreviously installed conventional propulsionsystem. In conventional drives, wherepropellers are attached to drive shafts, therotating shafts set up a swirl in the waterpreceding the propellers--a situation analogousto sailing upstream.Conventional propulsionRUDDER-PROPELLERLayout of Various Electrical Installations2 The design states that the Azipods aresuspended beneath the water line at the aft endof the ship, having the FP-propeller at the frontto move the ship through the water. In case oftwo Azipods, there is one Azipod on the portside (left facing forward) and one on the starboard side (right facing forward). Each Azipodis mounted on a shaft perpendicular to thecenter line of the ship's hull. The shaft can berotated to any position in 360 degrees. Theangular position of rotation can change thedirection of the ship's movement or keep itsailing straight ahead. Thus, ships with azipodsThis document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net

are steered without a rudder. For instance,Azipods are capable of moving the shipbackwards during docking. In this case podsare rotated to the 180-degree position, or theycan be positioned straight ahead (zero degreeposition) while the motors are reversed.5 Low noise and vibration characteristicsassociated with the conventional electric drivesystem are enhanced by Azipod motor’sunderwater location. Also the hull excitationsinduced by the propellers are very lowcompared to the conventional propellers.6 Azipod system facilitates extra space than theconventional ships. Space within the hullotherwise taken by propulsion motors andshaft lines is saved and can be used either forthe cargo storage or any other domesticrequirement on board. Azipods allow us todelete shafts, shaft bearings, rudders, thrustersalong with the rudder(s) and long shaft line(s),and associated equipment, which reducemaintenance and also improves efficiency.AZIPOD facing Forward in Twin Screw Vessel3 Much higher side thrust as the pods can berotated sideward and the direction propellercan be reversed thus eliminating the use of sidethrusters as in conventional drives sidethrusters, bow thruster are used to rotatesideward.4 Each Azipod can be operated independently ofthe other allowing subtle maneuvering. Theyhave short turning radius as compared toconventional rudder-propellers.Large engine use to turn propeller inConventional propulsion7 Azipod propulsion deliveries can be made latein the shipbuilding process significantlycutting dead-time investments costs. Modularconstruction reduces installation time andexpenses.8 Azipods offer safer cruising in harsh weatherand greater control in restricted passages.Reduced propeller induced vibration of theAzipod propulsion, possibilities to minimizehull noise by optimum layout arrangements,gearless and constant operation of diesels are aboon for the crew. Firstly ships with Azipodsystems have higher cruising speeds, notalways concurrent with fuel conservation,which may result in more or longer port calls.This also allows some lines to have itinerarieswith ports at greater distances from each other.This document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net

One best example that can be sited for instanceis as follows:- Norwegian Cruise Line'sNorwegian Star provides year-round Hawaiiservice with a visit to Fanning Island, Republicof Kiribati, about 600 miles from Hawaii, for aday at the beach. Traveling at about 25 knots,the Norwegian Star covers the distance in just24 hours, giving passengers two sea days--anda remote island call--on a seven-day cruise.9 Power requirement for twin-screw ships areless.10 Operational flexibility gives low fuelconsumption, reduced maintenance costs, It isreported that the operational efficiency if 15%more than the conventional propulsionresulting in high annual fuel saving, lessexhaust emissions and adequate redundancywith losses installation power. According toavailable statistics the vessel with carryingcapacity of 61,000-grt saves "up to 40 tons offuel per week." This is primarily due to theoverall improved efficiency of the Azipods.11 It saves lube oil consumption than in shaftdriven, some 10 liters of lube oil consumptionagainst 1000 liters in the conventional drives.In the construction of the first Azipodequipped cruise ship, the Carnival cruise LinesElation, approximately 100 tons was savedover previous ships with conventional driveand an 8% improvement in propulsionefficiency resulted in fuel savings of 40tons/week.Disadvantage• Higher capital loss• Diesel electric system required (power loss ,thepower generation is Diesel based)• Power requirement is higher for single screwvessels• Limitation in power• Limitation in speedMaximum powerper unitMaximumpossible speedMax. propellerdiameterLimitations uptillnow21MW26Kts6mLimitations uptill nowAnd in thefuture32MW30Kts8mThese limitations reduce the applicability of podpropulsion for fast ships and for the ships with veryhigh power requirement.Power (in KW) Vs Propeller Speed (in rpm)Environment and Azipod:The power plant concept offers anadvantage in meeting low emission standards. Emissionanalysis shows that diesel engines produce considerablymore nitrogen oxides when operated at variable speedThis document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net

than at constant speed. Since the Azipod system entailspower plant engines (generators) operating at constantspeeds and close to optimum power, the exhaustemissions to the environment are reduced. Thisenvironmental aspect will obviously become ofincreasing importance in near future, especially for theselection of machinery for ships operating on costalroutes.Environmental Impact1 Reduced exhaust emission.2 Improved safety by :• System redundancy.• Equipment reliability• Excellent maneuverability.3. Very efficient in dynamic positioning.• Need for anchoring and erosion of seabed decreases.Other Featuresi. The amount of heat generated is far lessin the system.ii. Long lasting equipment.iii. Recycling.iv. Easy disposal of material and parts.Protective FeaturesThe propulsion system includes several protectivefunctions.Major goal for the protections is to prevent“black out situations”. In normal circumstances thepropulsion system is the biggest consumer in theelectric network of the ship. Therefore the protectivefunction of Azipod is to ensure that propulsion systemitself does not generate blackout conditions. In order toknow the amount of the available power and thenumber of generators connected, the propulsion systemsupervises the status of the supply network, the statussignals for the breakers as well as the generators loadsare essential for network monitoring.Overload prevention or componentmalfunction may require propulsion power reduction.Possible reasons for reduction are explained in thefollowing sections.fresh water environments. All material combinationsare carefully studied to avoid corrosion.Machinery OnboardThe power plant's engines that drive the electricgenerators on today's azipod-propelled vessels are oftwo basic types:• Diesel• Turbine.Diesel engines operate onthe same principles used in cars and trucks that isInterrnal combustion engines. Turbine engines aresimilar in design to those on jet airplanes. One of themany criteria that the ship consider in choosing theengine type was the environmental impact of theexhaust smoke from ship funnels. Environmentallyfriendly, smokeless power-generation systems releaseno soot or visible smoke. Smokeless engines for thepower-generation system would be ideal. Today manyships have advanced-design turbine engines thatapproach this smokeless goal, partly by using a morerefined, cleaner-burning fuel.Latest Developments in Azipod Technology:The first version of the Azipod system was developedfor icebreakers, passenger ships, and tankers. The latestAzipod generation, currently in the launch phase, isknown as the CRP (contra-rotating propulsion) Azipod,developed jointly by ABB and Samsung, this is suitablefor a wide range of ships, from oil and LNG tankers toRoRo vessels. Based on the principle of contra-rotatingpropulsion (CRP), this new system consists of aconventional propeller system and an Azipod rudderpropellerrotating in opposite directions. The Azipodunit is located in line with the shaft-driven mainpropeller, without being physically connected to it, andoffers an alternative to designs that use two propellershafts.(a)Available Power in Supply NetworkAzipod control calculates the available power forpropulsion system. It depends on the generators andconsumers connected to the network.(b)Prime Mover Overload LimitThe prime mover load limit control works in such away that the power of any prime mover will neverexceed nominal value.Corrosion Protection:Azipod corrosion protection is performed with galvaniczinc anodes secured on the shell plating and azipodhousing. Material selections are based on both sea andContra-Rotating Propulsion (CRP)This document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net

More than 100 Azipod systems have been delivered todate, for use in liners, ice-breakers, supply ships,drilling rigs, and car ferries; the combined operating lifeof these units already exceeds 600,000 hours. Themajority are first-generation units. A total of eightCompact Azipod systems have been delivered, andorders have been secured for a further 25. The QueenMary 2 plans to have a maximum speed of 30knots,which will be helpful in establishing a regulartrans-Atlantic schedule of crossings, even inmidwinter's stormy weather.With the launch of the CRP Azipodsystem, the sales potential of the technology has beenfurther extended. Two RoRo vessels fitted with theCRP Azipod system will be delivered to Japan’s Shin-Nihonkai Ferry Company in 2004. Displacing 17,000GRT, these vessels will be the largest and fastest shipsof their size in Japan.Conclusion:From the discussions done in the last pages, it isobvious that The Azipod propulsion gives rathernoiseless and vibration less, comfortabletransportations, more carrying capacity, highmaneuverability as well as very flexible layout in termsof design. This system has a very flexible power systemand the requirement of spare parts is even low then theconventional ones.However, there are certain defects and technical flawsin each of the systems be conventional orunconventional one and considering all of the factorsinvolved, we, the authors feel that for the present timeAzipod systems will be in vogue and with thedevelopment of new technologies.Bibiliography:All the information furnished in thistechnical paper is collected from the following sources.i. ‘Marine Diesel Engines’by D K sanyalii. ‘Pounders marine dieselengines’.iii. ‘Marine auxiliarymachnies’ byHD McGeorgeiv. www.abb.com/marinev. www.mmd.comvi. www.abb.com/motors&drivesvii. www.hightechnologyfinland.comviii. www.marinelog.comix. ‘Basic Ship Structure’ –D.J.Eyersx. Reed’s ‘Ship Constuction’:Thomas Reed PublicationVessel Type Power(MW)AzipodunitsMV Seili Bouy 13 1TenderMT Uikku Product 11.8 1TankerMT Lunni Product 11.8 1TankerIB Rothelstein Icebreaker 1.1 2IBSVArcticaborgIcebreakingsupply3.3 2IBSVAntarcticaborgIB BothnicaMTNewbuilding1MTNewbuilding2(details till 2001)vesselIcebreakingsupplyvesselMultipurposeicebreaker3.3 28 2Tanker 20 1Tanker 20 1This document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net