On the crest of a wave

When he moved house more than a decade ago, US boat designer David Borman soon began to miss the picnic lunches he had enjoyed with his family 130 miles further up the Florida coast.

Pestered by his children but unable to afford a ‘billionaire power boat’ that would make the journey possible, he began to draw up plans for a vessel that would offer the same performance at a fraction of the cost.

The strange-looking vehicle that now sits in his workshop — part batmobile, part aircraft, and part speedboat — is evidence that the family picnics could be back on again soon.

The Sea Phantom, developed through Borman’s company International Maritime Flight Dynamics, is a high-performance powerboat with a difference. Instead of using a mixture of conventional boat design theory and brute force to batter its way through the oceans, the vessel flies just above the wave crests on proprietary shock-dampened aerofoils, radically reducing hydrodynamic drag and with it, fuel consumption. It represents, said Borman, a quantum leap in efficiency.

The craft begins its journey like a regular boat then, at about 35mph, curved aerofoils drop down from its wings and air flowing under the craft lifts it out of the water, elevating passengers to 8ft above the waves.

It is designed so that when it reaches its cruising speed of more than 100mph, only a tiny portion of its structure is in the water. With just the tips of the propeller and the aerofoils tracing a line in the surf, Borman said 85 per cent of the craft is carried aerodynamically. The Sea Phantom at full tilt is, he said, more like an aircraft travelling at speed down a runway than a boat.

This is not a flippant comparison. Borman said the Sea Phantom can generate twice the aerodynamic lift of an offshore raceboat by turning conventional boat design theory on its head and borrowing from the aerospace industry. ‘It’s impossible to maintain stable subsonic flight unless the centre of gravity is in front of the centre of lift, and that’s why raceboats do backflips. All the weight — engine, drives, fuel and batteries — is in the back. The Sea Phantom starts out passively stable through the air like a glider so when I launch off a wave it doesn’t want to flip over backward, it just wants to float until it hits the next one.’

He said the resulting vehicle is almost as efficient as an aircraft; an astonishing claim for a vehicle designed to travel through the water, a medium 800 times denser than air. ‘You can’t get much more inefficient than trying to push a boat at 50mph through the water,’ he said, pointing to a powerboat developed earlier in his career that burned 200 gallons of fuel an hour, had 3,600hp and did 105mph. ‘If you put 3,600hp in an aircraft you would be pushing the speed of sound.’

By contrast, in early tests the existing Sea Phantom prototype, which weighs 4,000lbs (1,818kg) has, claimed Borman, consistently averaged speeds in the mid-70s on less than 180hp.

The principle of operation resembles that of so-called Wing in ground effect vehicles or WIGs — boats with wings that float above the surface of the water on a cushion of high-pressure air created by the aerodynamic interaction between the wing and the water surface.

There have been many attempts to develop these fascinating vehicles and few more intriguing than Russia’s Cold War efforts to develop giant troop carriers able to sneak beneath radar systems. But according to Borman, most of these attempts have been let down by their heavy reliance on aerospace engineers.

While the Sea Phantom exploits similar aerodynamic properties, Borman said it is one of the first of its kind to be developed by a boat builder. ‘95 per cent of all past efforts have been undertaken by aerospace engineers, and if you’re going to go to all the trouble and expense of building a craft as complicated and expensive as an aircraft that stays on the ground — why not just build the airplane?’ he said.

So despite its bizarre appearance and heavy debt to aerospace engineering principles the Sea Phantom is, insisted Borman, a boat. ‘It operates under WIG principles but is definitely a boat — it can’t leave the water, and it uses conventional off-the-shelf race boat propulsion gear that has decades of R&D behind it.’

The big problem with applying aerospace techniques and materials to the development of such a vessel is that they are not rugged enough, claimed Borman. ‘The structure of the Sea Phantom has to withstand about five times the structural loads of a space shuttle on launch. Hitting an 8ft wave at 100mph for a fraction of a second creates between 20 and 40g load on the structure. That’s outside the realm of thought of any aerospace engineer.’

Although some of Sea Phantom’s components — most notably its propulsion system — have been sourced from the racing boat industry, Borman has had to look beyond conventional suppliers, and estimates 80 per cent of the vessel is based on surplus military technology.

‘There is no available civilian technology to make a craft light enough to operate in complete free flight and sturdy enough to hit a wave at 100mph without disintegrating. That’s a big problem when you’re flying a couple of metres off the water and you’re in a structure where theoretically every seventh wave is 50 per cent higher than the other six.’

Clearly, reacting to this seventh wave is important, and Borman has developed an elegantly simple passive suspension system that responds rapidly to variable sea states. This contrasts with the aerospace industry’s attempts to solve the same problem.

‘Many aerospace engineers have attempted to find a solution using fly-by-wire control systems where they’ve got forward looking lidar, infrared, and so on. If a fly-by-wire control system goes out at 30,000ft you’ve got 20 minutes to decide what you’re going to do about it, but if it goes at 6ft it’s going to disintegrate. You’re going to die. The other problem is the expense — once you start piling in gear like that you end up with no economic reason to exist.’

Borman believes he has strong economic reasons to exist and, after completing early sea trials, he is applying the finishing touches to his proof of concept model, a 34ft, five-passenger prototype powered by a 10-cylinder, 625hp engine developed by UK company Ilmor Engineering.

First production models are expected to cost $400,000-500,000 (£200,000-250,000), but with the design becoming more efficient as it is scaled up Borman plans to develop a range of models capable of carrying up to 21 passengers.

Though he has had several visits from US special forces, Borman confessed he is glad he hasn’t sold the technology to the military as his primary ambition is to sell production versions of the Sea Phantom to wealthy power boat fanatics, emergency services and commercial operators. ‘That’s where it gets really practical — it can make triple-digit speed available to people that can’t afford an aircraft ticket.’