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Super sub scores winner

An 'underwater Ferrari' that could also offer low cost inspection is waiting for the green light. Dave Parker reports on how one structural engineer's dream took shape.

Sitting on its trolley in an Essex barn, the Subeo Gemini submersible looks sleek, sophisticated and sexy. This is no accident, says Subeo managing director Bob Leeds.

'We put a lot of effort into the fibreglass bodywork. In fact this turned out to be our biggest challenge. But the market sector we're interested in will demand something that looks more like an underwater sports car than a piece of industrial equipment.'

Leeds, whose mainstream activity is structural design for the construction industry, admits that Gemini is the culmination of a life-long dream. As a child he was captivated by the story of Captain Nemo and the Nautilus in 20,000 Leagues under the Sea. 'When I grew up I took up diving as a hobby, then became a professional air diver, working as a marine inspector in the Middle East and the North Sea.

'But this was still a long way from my dream of gliding along coral reefs in shirt-sleeve comfort, like Captain Nemo.'

About five years ago Leeds began to define his ideal submersible in detail. It had to be a lot more user friendly than other small submersibles currently on the market. Expensive support vessels were out. 'My concept was a two-seat craft with reasonable surface capability that could be tied up to a jetty or hung off the stern of a large yacht, ' he says. 'And it would be limited to a maximum depth of 50m.'

Most commercial and research submersibles can dive much deeper than this, of course. Keeping to the 50m limit, however, offers more than much lower stresses on the pressure hull, Leeds points out.

'If anything goes wrong, you can simply flood the hull, open the hatches and float up to the surface using normal breathing apparatus.'

Further simplification comes from the decision to do without the thrusters that most small submersibles rely on for attitude control at low speeds. Instead, Gemini relies on a 150kg moveable lead weight for fore and aft trim and the transfer of water ballast for roll trim. Front and rear hydroplanes and a rudder take over as speed increases. In this aspect Gemini resembles the classic military submarine more than a modern submersible - but there is a potential drawback in this quest for simplicity.

'Submarines that depend on trim tanks and hydroplanes usually need large crews to operate them safely, ' Leeds says. 'Even a craft as basic as Gemini would probably require three or four crew members. The secret is to do everything through a programmable logic controller: that way one man can drive it.' (See box) However clever the concept may have been, Leeds' dream may well have remained a fantasy had not a friend advised him that his project could well be eligible for an innovation grant from the Department of Trade & Industry. 'We were based in the north east Essex peninsula, and our ideas were classed as a high risk project. In the end we got £25,000 - which just about paid for the hatches.'

Serious construction began in 1995. Leeds did virtually all the design himself, subcontracting component manufacture to a wide range of suppliers. As much as possible he adapted existing components and technology.

The carbon steel pressure hull, for example, is welded up from two standard torospherical pressure vessel end sections from the Leeds & Bradford Boiler Co.

'Sophisticated finite element analysis was needed here because of the large openings for the hatches, ' Leeds reports.

A programmable logic controller - basically a very robust specialised computer - was sourced from the solvent recovery industry. This accepts input from a joystick controller and touch screen, operating valves, pumps and hydroplanes as required to produce the desired response. It also acts as a safety monitor, preventing the vessel from submerging with the hatches open, for example, or refusing to let it descend below the 50m limit.

As construction proceeded Leeds began to appreciate the size of the challenge. 'It's much more demanding than designing and building a light aircraft, for example, ' he insists. 'A submersible has to work underwater in a corrosive environment. And even at only 50m there's 14t of pressure on the hatches.'

By May last year the project had moved to its current home, a barn on a farm near Harwich belonging to a diving friend of Leeds. Its main advantage is the presence on the farm of a small reservoir, just big enough and deep enough to carry out initial tests. On 27 August last year, in the presence of Commodore David Russell, deputy flag officer HM Submarines, Gemini was formally launched into its natural element.

'Our only problem was that the reservoir's so small we can't get up to full speed, ' Leeds reports. 'Otherwise it was something of an anti-climax.

Now we're waiting for classification from Lloyds so we can begin using it commercially - and soon we're off to Spain to make some films with TV companies.'

Subeo has yet to set a price on Gemini. Leeds says only that a US-based company is offering to produce a similar craft for something over £400,000, but Gemini will be significantly cheaper than that. Apart from the rich man's toy role, Subeo believes Geminis could be used for everything from inspecting subsurface pipelines in shallow waters to patrolling coral reefs at risk from poaching. And can it be long before James Bond climbs into one?

Looking back at the last five years, Leeds says: 'If I'd known how hard it was going to be I probably would never have started.' But many will envy him all the same.

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