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Systems Articles |
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From time to time, this page will be liven up with general description articles regarding various systems, functioning, technic or design we can find on modern cruise ships. Since these articles will be available in the forum too (but without images), you're free to react, to add your own commentaries, precision, or to add your experience and knowledge. If you would like a specific system to be treated here, simply ask it directly through the forum or e-mail me, I'll try to do it, with the help of other readers if they want.
Articles yet available:
- Gas-turbine propulsion system
Pod-propulsion system:
Here are few datas about ELATION / PARADISE and MILLENNIUM pods: - ELATION: 2 azipods, developed by ABB Marine, adjustable on 360°of 14,000 kw each, running at variable speed (that's why azipod systems and diesel-electric ones in general, needn't variable pitch blades propellers but fix ones, a substantial economy and simplification regarding propellers) between 0 to 146 turns/min.. Of course, to go astern during manoeuvres or to brake the ship, the rotation is reversible, electrically by inverting polarities and 20 secondes are necessary to go from full ahead to full astern. The electric motor inside the pod is fed with a tension of 6660 V. The whole pod is 170 tonnes heavy and can operate a 180° turn in 22.5 secondes. |
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| Azipod model. (source: Kvaerner Masa yards) |
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Compared to the traditional inboard elecric engines / shafts of the other ships of the same class (FANTASY...), the general output is improved by 8%. More, they are lot of more manoeuvrable and the gyration's diameter is 35% reduced. The electric engine and working parts are cooled with air. We have to notice too, these pods have no fire extinguishing's system. Indeed, in case of fire in the pod, a smoke's detector stop immediately the ventilation and the resulting absence of oxygen in conjugation with the natural cooling because of the exterior sea water's circulation would stop flames. |
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Azipods installation aboard ELATION and PARADISE. (source: Kvaerner Masa yards) |
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- MILLENNIUM: 2 Mermaid pods, design resulting of a collaboration between Alstom and KaMeWa, 19,500 kw each and a general functioning comparable to the ABB Marine ones above. To sum up, the main advantages are: - far best manoeuvre ability, (so economies too. y the way FANTASYs, without pods and with their 3 stern thrusters of 1,5 Mw each, are already able to manoeuvre near a quay without tug's assistance until 35 kts winds and this despite their 7,600 m² of longitudinal sail's surface, so you can imagine to use the whole power - 2 X 14 Mw - as a lateral thrust in case of short emergency with the pod's ships). - best output so economies of exploitation - absence of stern thrusters, shafts, less bearings. - better comfort because of lower level of vibrations. - better flexibility during the construction since the propulsion's engines can be set after, avoiding few delay's problems and permitting the continuation of the other rooms (or blocs setting) in the hull. - gain of volume for the addition of more lucrative spaces for passengers, - faster and easier maintenance (especially in the case of very serious failure of electric propulsion engine which needs its replacement in shipyards), so economy of exploitation. The diameter of propellers is about the same than for traditional systems one (but pod system is now the traditional one!), so about 6 meters. Accidents and risks of damages with pods in case of the ship runs aground are about the same than with any ship. I don't think; in case of very serious damages, it would be more difficult and slow to change a pod than a whole shaft/bearings/supports/watertight supports/propellers/rudders line, it seems it would rather be the contrary. In the ELATION and PARADISE, the very aft structure of the hull has been reinforced to support the additional weight and thrust's strength due to the azipods. These pods and their propellers, are not under the keel level and so are not more exposed than a shaft system. We can even say, because of the better manoeuvrability and reaction in case of emergency depicted above, risks to occur impacts are theoretically smaller. |
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ELATION's stern with the two rotating Azipods. (source: Kvaerner Masa Yards)
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| VOYAGER OF THE SEAS's stern with the two rotating Azipods and one central Fixipod. (source: Kvaerner Masa Yards) (photo graciously sent to me by Romain). |
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To finish, advantages and reliability of pods have been widely demonstrated (a 11,4 Mw azipod had been tested first by ABB with a tanker in -30° C air conditions in very cold waters and that was absolutely conclusive). Last year troubles with PARADISE are not due to pod's principle but because of a defective watertight seal so the sea water entered in the pod. The delay (and so the cancelation of few cruises) to repair it was mostly due to delay of livraison of spares from European firms than a big problem about the principle or the realization and reliability of the pod system itself. Even better, the MILLENNIUM's problems during her maiden cruise was not due to pods at all as first rumours said and even not because of it gas-turbine system! The cause was "simply" a break box in the electrical circuit between alternators driven by gas-turbines and the electric engines of the pods. This break box, after the problem was localized, was first bypassed to allow electrical feed of the propulsion engines, and then replaced (or repaired) at Rostock in Germany during an afternoon and an evening "only". The type of breakdown which can happen with any classical diesel-electric ship. Of course, other breakdowns with pods (or gas-turbines) can and will probably arrive, but this is the case with any mechanical or electrical device. In about three years of exploitation, ELATION and PARADISE had not occurred particular serious problems with their pods. Same thing with VOYAGER OF THE SEAS. Of course, as I'm interested (and probably other readers) in informations about that, all additional ones are greatly welcomed.
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