Double bubble?

British yacht designer Christian Stimson has reconciled the contradictory demands of lifeboats and tenders in a single craft that will not only save weight and deck space on superyachts, but also blend in with the aesthetics of the mother vessel. bob greenwood reports.

Originality, eye-catching styling, dazzling performance, air-conditioned luxury, EC Recreational Craft Directive compliance — none of these attributes appear in the SOLAS list of ‘must-haves’ for lifeboats. Similarly, the ability to be rowed is not usually a requirement for superyacht tenders and nor would they normally be expected to withstand freefall launching vertically or horizontally from a great height.

Since the function of lifeboats is to save lives, they need to be sturdy and safe, but usually they don’t need to move at more than displacement speeds. They must have sufficient transverse flexibility, measured by a swing test, to absorb energy without excessive accelerations on the occupants. Yet they must also have high longitudinal stiffness, so that there’s minimal deflection between lift points even when loaded to double capacity. At the same time they must have the global strength with variable stiffness to pass a drop test, absorbing energy, while not deforming to the extent that doors, hatches, engine mounts and other mechanisms no longer function.

“Chopped strand mat can do the job, but that makes for a heavy structure, albeit a relatively low-cost structure,” says yacht designer Christian Stimson, whose engineering and materials expertise is usually employed at the opposite end of the spectrum with more exotic composites and high-performance craft. “Higher spec materials are more obvious when it comes to high-performance craft, sleek superyacht tenders included, but they have seldom been first choice when it comes to life preservation. But once you consider using lightweight and strong composite structures, accommodating the opposing operational demands of tenders and lifeboats in a single vessel is more than possible.”

Indeed, Stimson can see significant advantages to superyacht owners of having a craft that satisfies SOLAS lifeboat standards, as well as qualifies for a CE mark under RCD rules. He reasons that such a solution would not only release deck space, but could also translate to less weight in the wrong place. There could also be further savings as regards crane specifications.

“With two boats in one, costs could be a lot less than for a lifeboat and a separate tender,” says Stimson. “Indeed, in many cases savings could actually be doubled — as two lifeboats are required for the larger superyachts and most prefer to carry two tenders.”

He also believes there are gains to be had aesthetically. Rather than stick out like a sore thumb, as conventional lifeboats often do, a new dual-role craft could be made to blend in with the overall design concept of its mother ship.
With his design business based in Cowes, Isle of Wight, Stimson is probably best known for high-profile leading-edge performance sailboats. The best known of those include the canting-keel yachts Full Pelt X (11m/36ft) and Big Grin (9m/30ft), the 11.6m Reflex 38 and, more recently, the 18.3m (60ft) SDG60. However, he has other boat design credits. Often working in partnership with stylist Roel de Groot, who has worked on several production powercruiser projects for clients such as Princess Yachts, Stimson’s portfolio also includes a 13.7m (45ft) power-catamaran, an 8.5m (28ft) production RIB and a 45kt superyacht RIB-tender.

As well as private owners and marine industry clients, Stimson has carried out work for the Royal National Lifeboat Institution, Trinity House and the British government’s Ministry of Defence. Nothing has tested the range of his engineering knowledge and design flair, however, quite so much as his latest venture, the Superyacht Lifeboat-Tender. Despite the formidable technical challenges that such a hybrid presents, he is sure that he has now found a viable solution.

As for the market for such a dual-role craft, Stimson is convinced that he has come up with what superyacht owners and captains want. And he has done his homework, having completed a market research tour of the European heartland of the superyacht industry, the Côte d’Azur, a few years ago.

“The original purpose of that trip was to prospect for superyacht tender commissions, but in meeting after meeting with brokers and captains of large displacement yachts, the same message kept coming back,” recalls Stimson. “They wanted to go faster, lighter and narrower, and if they could roll the duties of tender and lifeboat together in one vessel that, they said, would be a big step in the right direction.”

On his return he wasted little time in laying down some structural ideas on computer to produce a structural design, onto which his associate Roel de Groot overlaid some styling interpretations. Stimson then put together a presentation package with which he was successful in applying to the UK government’s Department of Trade and Industry for funding in the form of a £45,000 (E60,000) SMART Award. This grant was supplemented by private funds to give a total budget of £60,000 (E120,000), which enabled him to carry out a six-month feasibility study to investigate the practicality and commercial viability of producing a 10m (33ft) vessel that combined the roles of SOLAS lifeboat and superyacht tender. Part of the process included seeking help and advice from materials producers, structural engineers, superyacht management companies and various MCA (Marine Coastguard Agency) personnel. He also did some 3D modelling.

The design brief he initially imposed on himself was for a semi-enclosed boat that could plane at more than 30kt, accommodate up to 16 guests and two crew in tender mode and, initially, up to 35 people in lifeboat mode — although the latter figure was subsequently raised to 45. With a single engine it would also need to be rowed in order to comply with SOLAS, so rowlocks and sweeps had to be factored in too.

Also, to enable the craft to be adapted to the styling of its mother ship, the project brief called for non-structural ‘cladding’ to be used over a structural frame. “The structural concept was the single most significant and complex issue to resolve,” recalls Stimson. “We needed to standardise structures to reduce costs, while allowing for looks in keeping with highly bespoke mother ship styling.”

The solution that he came up with was a cage-like structure, a foam-cored laminate frame. “It could be done with a wet lay-up — say, using a Corecell structural foam core and epoxy/E-glass laminates and where localised stresses demand, carbonfibre,” says Stimson. “The skill base needed to produce this will not be top end…”

The pretty bits, foam-cored FRP panels, would attach to the structural cage. They can be customised to reflect any styling of the mother vessel. For Roel de Groot, the styling presented some particularly tough challenges, as he has had to marry the demands of the functional people carrier with those of a sleek express-style cruiser.

And passengers are also going to require comfort and convenience. “This has got to be a boat that will serve in hot climates, therefore air-conditioning and ventilation are a must,” says Stimson. Armchair seating set all around the internal perimeter of the hull will also make passengers comfortable and keep them safe in a light and airy deck space with large windows that run the length of the superstructure. Big sliding side doors and a stern ramp will provide for getting in and out. Save for a head compartment amidships, the passenger deck is completely uncluttered, as the helm station is contained in a streamlined wheelhouse that sits on top of the craft.

Not the least of Stimson and de Groot’s problems was the accommodation of SOLAS requirements for high visibility. While ‘Day-Glo’ orange or fluorescent lime green hull and topsides are perhaps not the most used colours of the yacht stylist’s palette, a compromise has been found that will satisfy the likes of the MCA and those concerned with mother ship aesthetics — bands of high visibility colour.

Certainly initial feedback from superyacht builders, owners, captains and yacht management companies to the Lifeboat-Tender concept has been very positive, says Stimson. “One common criticism, however, is that what we’ve come up with is too small. Although we chose 10m (33ft) for the feasibility study, it seems the industry really wants a larger vessel still… They’ve indicated that 13-16m (43-52ft) is more appropriate. And they also want twin engines for speed and reliability, which means that the vessel won’t need to be ‘rowable’ in order to conform with SOLAS.”

Accordingly, Stimson has revised his design, making it longer and sleeker — 15.5m in all. “The engineering for the layout has not been carried out yet,” he says, “but we’re a quarter of the way up the pyramid. For lightness and strength, we’ll possibly use carbon and Kevlar, with an 80°C post cure, like modern racing sailboats, but infusion is also an option if production volumes justify it.”

Only one major hurdle now remains — selling the first boat with only drawings and a tank-test model to show. “Alas, just before Christmas a commission from a German superyacht yard was narrowly missed,” says Stimson. “But there are another eight to 10 ‘hot prospects’ out there… We’ll wait and see.”
He doesn’t rule out building a boat speculatively, however, which would mean applying again for a government grant and putting in a sizeable investment of his own. In the meantime, his main investment is necessarily in promotion.

Lateral Thinking

Before tackling the ‘lifeboat as tender’ project, Christian Stimson had already dealt with several challenging demands as regards tenders. For instance, this 8.5m (28ft) RIB designed for the Farr 115 yacht Sojana owned by GBR Challenge America’s Cup campaigner Peter Harrison. The 60hp Steyr sterndrive-powered tender had to be light enough to be raised by the yacht’s mizzen boom, small enough to fit into a cramped lazarette, but still carry up to 14 passengers. The answers were provided by a 2m (7ft) removable bow that allows the tender to fit diagonally into its 6m (20ft)-long compartment. The RIB has a dihedral bulkhead with a three-pin bow latching, while the target weight of 1,100kg was met with the help of titanium components and composite construction. The use of female moulds, says Stimson, also meant the weight of fairing materials and paint could be significantly reduced..

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