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Shinkai: Inside the design journey of the superyacht designed for deep-ocean adventures

6 March 2024 • Written by Roger Lean-Vercoe

With a name meaning "deep sea” in Japanese, the 55-metre Feadship explorer yacht Shinkai is packed with ocean-going accessories including a  7.2-tonne, three-person submarine and Toyota Land Cruiser. Currently turning heads in Hawaii, designer Phillipe Briand breaks down her brief and build...

“Designing explorers – boats with a meaningful purpose – really interests me,” says Philippe Briand, a naval architect whose 30-year career can be traced through the 12,000 or more yachts conceived on his drawing board: a multitude of race-winning custom sailboats, a huge number of cruising yachts from production builders Beneteau and Jeanneau and, latterly, a series of elegant custom superyachts bearing the stamp of his award-winning Vitruvius brand.

Image: Feadship

So when approached by a superyacht owner with a desire to explore high-latitude waters – not just above the waves, but also beneath – his attention was truly grabbed by the challenge. “This highly experienced client had plenty of ideas as to how he might achieve his goal,” Briand explains, “including the possibility of a ‘submarine yacht’ – an idea that was eventually decided to be just too far ahead of its time.”

The brief eventually evolved into a highly-customised 50-metre explorer, whose prime task was to carry and operate a three-man submarine. “Of course,” Briand continues, “the boat still had to have all the luxury of a superyacht and carry a normal complement of tenders and toys, as well as a Toyota Land Cruiser and an all-electric Jet-Ski, so the 50-metre target size was under pressure from the very start of the design process.” The ‘high latitude’ requirement, including a desire by the owner to transit the Northeast Passage, further added to the complexity.

Image: Vitruvius

A 6.3-tonne, U-Boat Worx C-Explorer 3 was eventually selected as the submarine of choice. To allow its deployment in less than perfect sea conditions, a 7.0-tonne crane with an 8-metre reach, with stabilising lines running from the sub to deck winches on the mothership, was identified as the most reliable method of launch and recovery. This would be accomplished as a ‘launch-and-go’ operation with the three passengers boarding the sub before launch.

Image: Vitruvius

Breakthrough stabilisation

Then came the issue of the mothership’s stabilisation. “I was not keen on using conventional fin stabilisers,” explains the owner, “because they are rather inefficient at low speed and can be damaged by ice and flotsam, so I suggested that we should investigate the use of gyro-stabilisation, as I knew this is being used successfully in many smaller craft today.”

The technology is not new – Emily Cadwallader’s 136-metre motor yacht Savarona had been fitted with a gyro weighing 50-tonnes in 1931 – but this was never considered a satisfactory solution on larger yachts until recent technological advances, including the operation of the gyro in a vacuum and a tenfold increase in rotational speed to 2,000rpm, prompted its reemergence – but only in boats up to around 30 metres LOA.

Image: Feadship

The main downside of scaling such technology up to larger vessels is that the gyro installation will occupy a significant volume in the yacht, but for this project there were other considerations. At cruising speed the gyro’s performance is slightly inferior to fins, but, says Briand, “this deficiency can be partially rectified by adding long bilge-boards to the hull”. Going with a gyro would also eliminate ice-vulnerable hull appendages, increase the fuel efficiency of Briand’s already efficient hull form, and provide significant additional stability when launching the submarine and tenders, so it quickly became the most compelling option.

Image: Vitruvius

With this choice made, the final hurdle was to identify a manufacturer. “No one had ever built such a large and technologically advanced gyro, and just two manufacturers worldwide had the capability,” explains the owner, “Veem in Australia and GyroMarine in Italy – both of whom satisfied us that they could build what we needed. We eventually chose the Livorno-based GyroMarine for their Active Drive concept that is more attuned to the needs of larger vessels with slower roll rates.”

A custom-built GyroMarine GM600 Active Drive System gyro – at that time the world’s largest active drive system – was selected. This 23-tonne beast is housed within a 3.3m x 2.7m x 2.5m cube and develops an impressive 850kN of angular momentum (a measure of rotor size and speed) that delivers a stabilising torque of 1,000kN m, with peak power consumption of 70kW. “It was a unique experience for us to work with such a passionately interested owner,” says Tony Hands, the technical manager of GyroMarine’s Active Drive technology. “He certainly put us through our paces to create an ideal solution for this very exciting yacht.”

Image: Vitruvius

The Toyota Land Cruiser also called for special treatment. “I’ve carried vehicles on previous yachts,” says the owner, “but they rust really badly in salty air.” The answer was to treat the vehicle in the same careful manner as one would an embarked helicopter and store it in a sealed garage.

Finalising the design

With these technical parameters decided, together with identifying the need for six guest suites and generous accommodation for 12 crew, Briand could start design work. His approach was first to concentrate on the stern to locate the submarine, tenders, toys and gyro, to confirm that they could be accommodated within Briand’s slender 50-metre hull with its characteristic steep underwater rise at the stern – an essential element to meet the owner’s demand for fuel-efficiency.

Image: Vitruvius

While highly efficient, this hull shape limits the volume available in the stern sections for the internal stowage of tenders and other equipment so, as the design progressed, the yacht’s size not only grew to 55 metres but the decision was also taken to store the submarine on the open aft deck, together with the two tenders and the Land Cruiser. The submarine takes pride of place, centrally positioned in a shallow well at the stern with its huge Palfinger knuckle-boom launching crane on its starboard side. Just forward is the watertight box containing the Land Cruiser, a 5.7-metre SOLAS tender and its launching crane and an 8-metre limousine tender, launched by the sub’s crane. It’s a deck layout that permits sufficient below-deck volume to be allocated to the gyro.

With these items provisionally positioned, it became apparent that the elegant, low-profile design that is the trademark of Vitruvius designs would not provide sufficient volume for spacious accommodation. “I therefore pressed the owner to add an additional ‘owner’s deck’,” explains Briand, “rather than increase the length once again, which would make access to shelter and small harbours more difficult. After much discussion concerning the effect on the yacht’s aesthetics, this was eventually agreed.”

Image: Feadship

The remainder of the vessel offers all the luxury of a regular superyacht. Below an open observation deck, the uppermost enclosed deck contains the wheelhouse and captain’s cabin, while below is the owner’s deck featuring a full-beam dining room, two impressive suites and his and hers offices that provide panoramic views forward. Two spacious guest suites and two twin-bed children’s suites are located on the main deck together with the main saloon. Excluding the engine and gyro rooms, the crew have the lower deck to themselves, with seven cabins, a large mess room, laundry and galley.

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