BEYOND
ALL EXPECTATIONS

Sergio Cutolo - Naval Architect & Exterior Designer

HYDROTEC,
OVADA, 25 MAY 2021

FOCUS ON: EXPLORER YACHTING

An interview to Sergio Cutolo, fouder of Hydro Tec, who designed Aurelia’s bold exterior lines and developed her super-efficient naval architecture (not to mention her state-of-the-art engineering).

You designed the exterior line of Aurelia as well as all Flexplorers. Spaces on board Aurelia, 39.37 metres, are actually huge for a yacht of this size and the layout is extremely functional with plenty of space for storages, too. How did you succeed in combining an exterior that is not aesthetically heavy or voluminous with such roomy interiors? From a structural point of view, we have tried to minimise the impact of the structures on the hull and superstructures to maximise interior spaces. In the superstructure we have managed to create the perfect match between the designed internal layout and the positioning/size of the windows. The transverse frame, in line with the shipyard approach, allows for better spaces optimization, increasing the internal volume also thanks to the structural arrangement that requires limited space for internal structures. The hybrid structural arrangement, main longitudinal structures and transversal frames at 500 mm, also provides additional design flexibility, allowing for easier modications/customisation. A gallery/tank deck runs below the guest area to connect the engine room to the crew area. This technical space also allows easy access to equipment and tanks. Thanks to the hull’s large volume, easily accessible storage compartments and freezers are located below the crew area.

How you developed her naval architecture? The hull was preliminarily optimised using CFD analysis with particular attention to avoid any kind of interference between the various appendages (rudders, stabilizers, thruster, exhaust scoops, etc). Once the CFD analysis has been completed, the hull has been tank tested at MARIN Institute in Holland. The naval architectural aspects were influenced by the peculiar weight distribution and the profile of the bow which was designed according to the specific aesthetic needs of the owner. Hull lines were designed to improve efficiency and to match the weight distribution as well as interior space requirements.

On the occasion of sea trials - in all weather conditions - she proved to be even more efficient than expected. Would you please tell us what makes her so efficient? I’ll make a list of the key characteristics: Her hull is a typical fast displacement round bilge hull, with a bulbous bow and deep and flared in its forward sections to keep the deck dry in all weather conditions, even the worst, and to allow for optimal space for the crew area and for the Owner Suite. The hull has a generous bulbous arc and flat sections at the stern. The Beam/Draught ratio has been brought to an optimal value and special arrangements have been made to allow high diameter/high efficiency propellers. Towards the transom, transversal sections flatten and enlarge astern to allow large diameter propellers without affecting the draught and huge space for beach club and swim platform. Aurelia has two pairs of electro-driven stabilizing fins. This solution, which is not common on vessels of this size, has multiple beneficial effects. First, the four fins arrangement grants, by definition, for better course keeping because they cancel completely the steering effect caused by aft fins. In addition to that, Aurelia was designed also with independent electrically driven rudders that, thanks to a sophisticated software, work together with the four stabilizers furtherly improving coursekeeping and, consequently, seakeeping itself.

What are the main benefits of having four fins? Compared to two-fins installations, the four-fins installation allow for the installation of smaller machines and blades, offering redundancy in case of blade failure. In practice the experience showed that, during normal operation, the contribution of the aft fins to stabilization is about one third compared to the forward ones, so they be kept almost centered reducing any possibility of turbulence to the propellers. At anchor, the four fins work in synchrony to provide optimal stabilization.

As said at the beginning, Aurelia behaviour during the tough sea trials exceeded your expectations... Yes, indeed! Data from sea trials were excellent in all regards: the maximum speed has been more than 15 knots, exceeding by more than one knot the contract specifications. Also range calculations showed an incredible 7.000 nautical miles range at 10 knots, much higher than the contractual values, due to the extremely low fuel consumption which is about 70 l/h at a speed of about 10 knots. This amazing achievement is the result of the hull optimization combined with the perfect integration between the hull itself and the propulsion package (engines, gearboxes, propellers).

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