SHIPREPAIR AND CONVERSION TECHNOLOGY 2ND QUARTER 2004 3

AHUGE conversion project on the semi-submersible heavy-lift ship Blue

Marlin, by increasing the breadth of the hull,required upgrading of its propulsioncapabilities. Wärtsilä was one of the maincontractors for the task, which includedsupplying generating sets, two retractablebow thrusters, and a large high-efficiencynozzle with new propeller blades for themain propulsion plant.

Blue Marlin, originally built at CSBC, inKaohsiung, Taiwan, (newbuilding 726) wasdelivered in 2000 - her sister, Black Marlin,was presented in the RINA annualSignificant Ships of 1999. The vessel iscurrently owned by Dockwise, a Dutchcompany specialising in heavy transportshipping for the oil and gas industries. Shewas originally equipped with one open LipsCP propeller with a diameter of 6200mm,which was directly driven by a MAN B&W8S50MC-C low-speed diesel enginedelivering 12,640kW at 127rev/min. OneKawasaki transverse thruster was installed inthe bow.

The complex conversion task at HyundaiMipo Dockyard in South Korea requiredincreasing the breadth of the vessel from42m to 63m. With an enormous unobstructeddeck area of 11,227m2, Blue Marlin is nowbelieved to be the largest semi-submersiblevessel in the world. The deadweight of thevessel is 78,000dwt, enabling the vessel totransport heavy structures weighing up to73,000tonnes. With her new dimensions,Blue Marlin is able to transport heavier andultra-large floating production and drillingplatforms and larger semi-submersibledrilling units.

Propulsion requirements for the muchlarger converted vessel were investigated inmodel tests at MARIN in The Netherlands,

where sea-keeping tests revealed that morethrust was required to operate andmanoeuvre safely, especially in adverseweather conditions. To obtain this, two newretractable thrusters were proposed for thebow.

However, these two alone could not coverthe extra thrust needed, and it was alsonecessary to upgrade the existing main CPpropeller installation. In September 2002,Wärtsilä won the contract to supply threeWärtsilä 8L32-driven generating sets andtwo electrically driven Lips retractablethrusters. The order to supply a large LipsHR (high-efficiency) nozzle with newpropeller blades for the main propulsion trainwas placed slightly later in October last year.This contract also included model testing ofthe new propeller design at MARIN.

High-efficiency nozzle increasesthrust A Lips HR nozzle was installed around theexisting propeller to increase thrust withoutchanging the power of the engine - theexisting main engine, shaftline, and propellerhub could remain in place. A key reason forchoosing the HR nozzle was to maximise thebenefit of the installation of such a nozzle.According to Lips (today WärtsiläPropulsion), its HR nozzle differsconsiderably in shape compared with aconventional nozzle profile.

A curved outer profile and an inner profilethat flares out to the trailing edge increasesthe mass flow handled by the propeller. Thisleads to a larger pressure difference betweenthe inside and outside of the nozzle, resulting

in greater thrust on the nozzle. The Lips HRdesign is said to have proven to be verybeneficial in both free sailing and bollardconditions, providing up to 10% more thrustcompared with a conventional 19A nozzle.

New blade design with reduceddiameterThe hydrodynamic department of Wärtsilämade a completely new blade design to fulfilthe new requirements. The shape of thesewas challenging since many parameters wereoutside the normal range applied to nozzles.To limit tip speed, the original propellerdiameter of 6200mm was reduced to5200mm. The wake field at the aft of the shipwas investigated by measurements and tufttests. The wake field is important forpropeller design because it determines theinflow and therefore the cavitationbehaviour, hull pressure fluctuations, andchanges in thrust and torque during eachrevolution of the propeller blade.

A tunnel-headbox combination wasdesigned by MARIN to improve afterbodyflow towards the nozzle. The tunnel-headboxconstruction makes the wake field very closeto homogeneous in the axial direction, whichis favourable, and wake field measurementsshowed the beneficial working of thisfeature. The measured wake field was usedwhen designing the new propeller blades.When this design was finished, a model wasmade and several tests were performed atMARIN. The results showed an estimatedincrease in thrust of approximately 30% inbollard condition.

Two large Lips retractable thrusters of the

Extra width for Blue Marlin at Hyundai Mipo

Blue Marlin in drydock at Hyundai Mipo Dockyard, where the enormous extra width of the vessel(exceptionally wide at 63m, compared with 42m previously) only just fitted into the dock.

The newly constructed Lips nozzle. New CPpropeller blades were fitted later. Above and tothe left can be seen the remodelled semi-tunneladdition to the hull to provide improved waterflow.

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