wakefields, good cavitation behaviour and low excitation forces. We have much more freedom to use our imagination,” he adds.
Revolutionary aftbody MARIN has helped STX Europe in several fields. Using decades of experience STX Europe devel- oped a new revolutionary “Wave Damping Aftbody” using Computational Fluid Dynam- ics (CFD) software. The advantage of this aftbody is the absence of the typical aft shoulder crest wave, while at the same time, the deep wave trough and transom waves are also much smaller compared to earlier forms. With this new aftbody, the small bilge radi- us generates more flow in accordance with the buttock directions and prevents the flow turning in the centerline direction, so avoid- ing the typical low-pressure area in the aft- body. This low-pressure area is generated earlier in a typical wave crest location. Waves generated in the aftbody are now much smaller than they were in earlier vessels and wave resistance is much lower. “The new aftbody works best for fast, slen- der vessels, improving their fuel economy performance by 10 to 15%,” he says. STX Europe has also developed a new way of looking at springing/swinging behaviour for large cruise vessels. Now the shipyard
has a good understanding of the different forebody and aftbody form effects on swinging forces. “This is very important when huge cruise liners are considered,” Raimo stresses.
Performance and speed predictions have also improved by the help of CFD calcula- tions and prediction accuracies are much better than before, he says. High-speed, Wave Damping Aftbody ferries from Superfast III (1998) to Superspeed 1 (2008), have seen power levels drop by about 1% a year due to more effective hull, appendage and propulsion design. These latest technologies have also meant that the highest comfort class is now possible for even the very powerful and fast ropax vessels.
Close cooperation on the very larg- est liners MARIN and STX worked very closely on Oasis of the Seas. Here, a lot of R&D work was done before ordering the ship. Particular attention was paid to the springing behaviour and the effects of big beam and short rolling periods on the oper- ability of the ship. Steering tests were car- ried out in the pre-project stage in Miami port using four pods in the aftbody and two pods in the forebody. Raimo comments that in the hydrodynamic design the biggest
challenge was achieving high comfort levels during swinging behaviour, when the natu- ral frequencies of the hull are lower than earlier cruise liner designs. Another issue was the safe location of the very large 370-person lifeboats that are necessary for a 5,400-passenger cruise liner.
Equally challenging were the demanding manoeuvrability requirements for different ports compared to normal size cruise liners. The big beam was also a design challenge when looking at the cruise liner’s seakeep- ing behaviour. STX carried out extensive CFD studies together with RCCL, as well as wind tunnel tests to ensure high passenger comfort in terms of wind and exhaust gases, on the decks and promenade. The Oasis of the Seas is much more environmentally- friendly than earlier cruise liners and uses less fuel per passenger.
Skilled model basin staff Raimo says that MARIN has played an important role in the development of the very largest cruise liner. Being a prototype builder, STX Europe gives full-scale trial data to MARIN in order to improve and fine-tune things for future projects. This is very important to a prototype ship builder in order to improve accuracy for future projects, he says. Rules of thumb are
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