Solving the performance puzzle of superyacht Smeralda

Meeting Smeralda’s demand for fast ocean crossing ability with high fuel efficiency presented the design team with a range of issues. The formula of long waterline, narrow beam and lightweight construction had to be balanced against stability and a requirement for shallow draught for access to anchorages.

Resolving the naval architecture issues within Espen Øino’s design concept fell to a team of experts at Hanseatic Marine led by Nick Stark.

‘There are a multitude of yards producing large-volume 12 knot displacement boats,’ says Stark. ‘Our challenge was to produce a boat that can reposition quickly and get places others cannot.

‘You can make boats go fast by throwing money and brute force horsepower at them. But that solution is not serviceable in the long term. We were looking to meet the challenge without resorting to something that would burn the owner through cost and maintenance.

‘Achieving a long, narrow boat with the kind of finish that is expected of a yacht of this calibre, and maintaining stability within the bounds of SOLAS rules, involved a tightrope walk, but due diligence and relentless attention to detail yielded results.’

Weight control was critical, which required a high degree of engineering and structural optimisation, while low drag performance required a high degree of hull design optimisation.

This involved extensive use of finite element analysis (FEA) and computational fluid dynamics (CFD) – with much of the code written in-house. A number of hull models were subsequently tested in tanks both at SSPA in Sweden and at the Krylov Institute in St Petersburg – which agreed to rare, if not unique, access for a private application.

Long, narrow shapes are well known to provide low drag efficiency; look no further than top-level rowing shells. But rowing shells also demonstrate the problem: they have minimal stability. So the challenge is to produce a long, narrow hull that can meet the safety requirement of coping with the severe heeling conditions it would face in a Force 10 gale.

With a length to beam ratio of 7.7:1 (77m LOA and 10m beam), Smeralda is not as narrow as some large military vessels, or even the Queen Mary liner. But those examples achieve stability through weight and draught.

Smeralda, says Stark, is 30 to 40 per cent narrower than yachts of a similar size, which generally cruise at 12 to 14 knots, not 22 knots. And she meets the stability requirements with a draught of just 2.6m and a displacement of 560 tonnes.

Stability under way is one thing, but guests demand yachts that lie still in anchorages as well. This is assisted by two pairs of Quantum Zero Speed Ride Control stabilisers – one fore and one aft.

Stability and structural engineering were not the only issues. The reduced volume of the hull shape poses challenges for comfort and accommodation, and the placement of all the machinery and systems that run a yacht of this size.

‘You could always do with a metre or so more in the beam, but we did not allow ourselves that luxury,’ says Stark.

‘Different design and technical terrors strike at different times, but when you see it all come together in the form of a svelte sea creature working as it should, it makes it worthwhile.’

Smeralda is the third yacht in this series, with another 77m sistership already under construction and 82m and 100m versions in development. Stark says the knowledge gained by developing this concept has seen the yard constantly refining its building processes.

‘We are learning all the time, developing a tremendous base of intellectual property and finding better ways of sequencing tasks and understanding how different trades will best operate through the build,’ said Stark.

‘To see the thousands of small details that will probably go completely unnoticed by the world at large and know that they all represent a significant improvement in the overall quality and efficiency of the product is very satisfying,’ he says.

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