The custom superyacht market has tended to disregard power catamarans, but there are signs this is about to change. This Is It, previously known as Project Illusion is a 43.5-metre power catamaran in-build at The Italian Sea Group, she promises to usher in a new age of multihull design that will transform perceptions.

Catamaran design and construction is old enough to be well understood, but young enough to still hold some mystique. Large custom catamarans, sail or power, are a rare breed that make up only a tiny proportion of the superyacht fleet, a niche within a niche. This is surprising given they offer inherent stability, more living space, more efficiency and less draft than comparable monohulls – all characteristics that are usually top priorities for superyacht owners.Boxy, utilitarian design has not done the genre any favours. Take two quite recent power cat projects: 66-metre Hodor (Astilleros Armon) and 46-metre Charley (Echo Yachts). In these cases, the twin-hull configuration was chosen because it suited their function as support vessels for carrying tenders and toys. The aesthetics were less important. Even 44-metre Hemisphere (Pendennis), the largest privately owned sailing catamaran in the world, turns heads for her sheer size rather than her exterior design.

This Is It is completely different and the exterior design was a priority from the start. Admiral is understandably reluctant to reveal too much about its all-aluminium power cat before her launch, but radical styling, an asymmetric layout and huge glass windows promise to confound our expectations of what a catamaran should look like.

“The owner was largely unsatisfied with the lack of innovation found in new-build yachts and yachting today,” says Michel Chryssicopoulos, Global Managing Partner at IYC, acting as the owner’s representative. “His vision was to create something unique and groundbreaking from every point of view. We spoke to various designers, but in his eyes nothing was daring enough. As luck would have it, before abandoning the search all together, we were presented with a ‘crazy’ catamaran design by The Italian Sea Group, to which the owner got up from his seat and exclaimed ‘That’s it!’ without hesitation.”Not surprisingly, the innovative design presented significant technical challenges. Rated at 750GT, the project was developed completely in-house by The Italian Sea Group, but Lateral Naval Architects in the UK were brought in to optimise the structural engineering and naval architecture.

“This was a demanding project in a number of ways,” says James Roy, Managing Director at Lateral Naval Architects. “We have a lot of useful experience with commercial multihulls, but you’re never going to be able to take a commercial catamaran design and apply it to superyacht, even with some tweaks. For a start, the hulls on a fast ferry are much slimmer because they have no accommodation requirement. The process of hydrodynamic refinement might be the same, but you’re dealing with two fundamentally different vessels.”

The team had very little wriggle room to play with because This Is It had been sold based on a specific design and specification, as well as a redline speed of 20-plus knots. In each of its hulls the yacht will have a 2000 M96 series MTU engine and a 150kW CAT generator. Both engines and generators are IMO Tier III compliant, which created another challenge for the shipyard when it came to fitting the bulky SCR systems into the relatively narrow hulls.

Lateral Naval Architects

Lateral Naval Architects is the yacht division of BMT Nigel Gee that provides naval architecture and engineering services to the superyacht industry. Beyond its core competencies, it focuses on meaningful innovation to enable superyachts meet the demands of today's owners and those of the future. Projects like 110-metre Kaos and 109-metre Bravo Eugenia (Oceanco) presented demanding specifications requiring specialist knowledge and innovative solutions. BMT Nigel Gee also designed Chief Flying Sun (now Disco Volante GT), a 36-metre power catamaran with a top speed of 42 knots that was built by T-Craft in South Africa and delivered in 1992.“We certainly like a challenge,” says naval architect Michael Barakis. “In the case of This Is It it was sticking as close to the original concept as possible in order to make something that everybody was happy with. We couldn’t play it safe and add a few grammes here and there. Everything had to be spot on first time round because there was no time for reworking.”

Weight Watchers

Weight was a critical factor from the start, especially given the amount of glass. A catamaran’s long, skinny shape hulls mean that as the weight increases they tend to sink proportionally lower in the water than broad-beamed monohulls. The Displacement Designed Waterline (the volume allotted to the submerged part of the hulls) is used in calculations for the superstructure, stability and compliance with various Class societies.

Underestimating the displacement results in a disproportionate increase in wetted surface area, which in turn increases resistance. It can also lead to lower than intended clearance in the tunnel between the two hulls. Keeping the weight down not only improves speed potential and hydrodynamics, but also reduces overall loads so the hull and crossdeck structures can be built lighter using less material.“The biggest challenge has undoubtedly been controlling the weight,” says Primiano Protano, technical and build manager at Admiral Tecnomar. “Even a small variation in the designed displacement can dramatically affect the drag, trim and speed of the hulls, as well as reduce the height of the cross-deck clearance and increase the risk of wave slapping.”

To simulate physical phenomena and evaluate the structural and fluid dynamics, This Is It has been totally designed using Finite Element Analysis (FEA). Simply put, FEA is a numerical method for predicting how a part or assembly behaves under given conditions. As the basis for modern simulation software, it helps engineers identify areas of stress or strain in a design. The numerical results can then be used to optimise shape, geometry or other parameters and reduce the need for physical prototypes. When used in conjunction with CFD, FEA is a sophisticated tool in the design of large yachts for overcoming the tendency of naval architects to err on the conservative side when it comes to displacement.

“Structurally speaking, the challenge was not just the glass, but also the beautiful yet complex shape of the aluminium superstructure,” says Andy Douglas, Principal Structural Engineer at Lateral. “Our experience told us that we had to do full FEA of the whole structure, not only the hulls and cross-deck. This wasn’t just for verification purposes – it was integral to the design to make sure it all worked.”

Most commercial catamarans are approved for restricted service and limited by distance from a safe haven or weather conditions, but This Is It is certified by RINA for unrestricted navigation. Lateral drew on its previous experience and compared its findings with different sets of Class rules to ensure the structural engineering complied with regulations. In some cases, it discovered that the Class rules didn’t cover all the loads they were expecting. “When you combine malleable aluminium with large areas of glass, which doesn’t like flexing, it’s more about the structure’s deflection than its strength,” adds Michael Benakis, Senior Naval Architect at Lateral. “We couldn’t just throw more material at it because the overall weight was so critical. Yachts normally grow, which means more weight and volume. Here everything had to be contained.”

Ocean Marine Systems

OMS specialises in the custom design and manufacture of electric and hydraulic marine thrusters and subsea instrument deployment systems. Superyachts with OMC equipment installed include some of the biggest sailing superyachts in the world, including 106-metre Black Pearl (Oceanco), 93-metre Eos (Lurssen) and 85-metre Bold (Silver Yachts). They also built the titanium and carbon fibre bow thruster on Skorpios, the recording-breaking 43-metre maxi racer from Nautor Swan.

“The only reason why we can make electric retracting and swing thrusters is because of the evolution in compact but power dense permanent magnet motors,” says Mark Barwelll of OMS. “They are a quarter the size and weight of a traditional motor and that means we can also move it up and down on top of the thruster instead of having it bolted to the hull structure as used to be case. The development of permanent magnet technology over the last few years has been the driving force behind the push to save weight and increase efficiency.”Heart of Glass

A defining design characteristic of This Is It is the 600 square metres of curved glass and the sheer size of the individual panes. Supplied by Sunglass Industry in Italy, the largest pieces are 14 square metres and the total weight of glass is around 23 tonnes.The laminated glass was chemically toughened rather than heat tempered as it requires less material for the same strength and resistance (the thickest panes aboard This Is It are just 400mm, but strong enough not to require storm shutters). The chemical process toughens glass through a sodium and potassium ion-exchange process in a salt bath. It imparts not only higher strength and MOR (Modulus of Rupture or resistance to breaking in bending), but also higher surface quality for superior optics. Special plastic interlayers between the laminates adds further strength and protect against overheating in critical areas. All the windows will be bonded in place using adhesives.

Sunglass usually uses photogrammetry, the science and technology of obtaining accurate dimensions from photographic images, but because of the size of some of the glass panes, in this case the structure was measured using a 3D laser scanner to ensure the panes precisely match the spaces provided.

Holes in Hulls

As in large sailboats, big thruster holes in the bows would have increased drag and adversely affected the catamaran’s performance, so This Is It has retractable electric bow thrusters supplied by Ocean Marine Systems (OMS) that rely on compact but powerful permanent magnet motors. The design is especially suited to the catamaran’s deep-V hulls because the thruster can be fitted higher with a longer deployment stroke to clear the hull.

“Powerboats normally overcome the efficiencies of an open thruster tunnel with more horsepower, but the shipyard was chasing efficiency and wanted to achieve a certain speed with a defined number of kilowatts,” says Mark Barwell, sales director at OMS. “When the thruster is retracted the base plate closes the hole, and because it’s been faired to match the hull shape you basically don’t know it’s there.”An Even Keel

The hull forms were tank tested at the Model Basin in Vienna, but additionally MARIN in the the Netherlands was asked to carry out a numerical seakeeping assessment – an interesting collaboration between two organisations that are usually are competitors.

Key to the research was ensuring the correct weight distribution, which is harder to achieve in a catamaran because the centre of gravity is not necessarily where the weight is placed and unbalanced loading negatively affects trim and performance. Once you have the weight distribution and you know where the loads are, then you can see how the model reacts in water and calculate the ship motions or damping.

The tank tests in Vienna verified the hull separation to minimise the incidence of wave reflection between the two hulls that can result in increased resistance. Top speed was optimised with the addition of hydraulic interceptors mounted inside each propeller tunnel, which resulted in a three percent gain in powering performance.

After careful consideration it was decided that the inherent stability of the catamaran configuration precluded the need for stabilisers. Catamarans generally have a high GM or metacentric height, which makes them very stiff with a low natural roll period. In fact, roll is mostly eradicated by virtue of their width. Attaching fins or foils to the hulls to further enhance ride control is possible, but they would need to have a very large surface area to be effective, which would mean more weight and hence drag.

Related to the stabilisation issue was resonance, or the tendency of a vessel to oscillate with greater amplitude at certain wave frequencies. Wave periods in the Mediterranean are generally six to seven seconds and seven to eight seconds in the Caribbean. A vessel with a natural roll period within that range could result in more excitation due to resonance. In fact, most monohulls do fall within that range, but a lot can be done with stabilisation systems because they have low GM and low damping. Not so with catamarans.

“We asked where in the world the catamaran would be sailing, because then we can say whether the weight distribution and hull geometry is suitable for a specific area or not,” says Enrico della Valentina, Yachts Team Leader at MARIN. “Admiral was very interested in exploring the stabilisation options, but as the roll period is slightly outside the critical range we advised against it. Another factor is that roll is associated with beam seas, but at anchor you usually have bow or quarterly waves and catamarans respond much better at anchor in these conditions than most monohullls.”

Sunglass Industry

Sunglass Industry, part of the group that includes German glass specialist Sedak GmbH, is a leading glass manufacturer based near Padua, Italy, and specialising in the hot bending of glass. It has one of the largest machines in the world for the chemical tempering of glass and over the years it has supplied curved glass panes for cutting-edge architectural requiring maximum transparency, including Hamburg’s Elbe Philharmonic Hall and the Louis Vuitton Foundation in Paris. It is also a key supplier to the superyacht industry and made all the glass windows for the 75-metre Admiral Kenshò.

“The main challenge with This Is It was not so much the curved shapes, but the size of the panes,” says Lorenzo Neri from the nautical division of Sunglass Industry. “We’re used to working with compound curves, but we had to make the panes both very large and light. The advantage of having lighter, thinner glass is that it is also more flexible, more than you might imagine, which combined with elastic adhesives means it can flex to some extent with the aluminium structure.” The Last Word

This Is It is not the only large catamaran project in build at The Italian Sea Group: they are also working on a 46.5-metre sailing catamaran. In addition to other multihull projects by other brands, they point to something of a renaissiance of the catamaran configuration in a market dominated by monohull superyachts that all too often fall back on established technical platforms and unadventurous design solutions.

“This is one of the most exciting new build projects we’ve been involved with to date,” concludes Michel Chryssicopoulos of IYC. “It’s the perfect blend of an audacious owner with a thrilling vision and a shipyard that was up for the challenge.”

This article was originally published in Issue 1 of How To Build It, you can download the magazine for free here.