Christmas road test 2022: Griffon Hoverwork 12000TD

The hovercraft is unique in its ability to travel across both water and land, or an otherwise impassable mixture of the two. The Hovertravel service is the only year-round scheduled hovercraft service anywhere in the world, in the summer departing as often as every 15 minutes. Fittingly, if somewhat belatedly, it’s the first hovercraft to become the subject of Autocar’s Christmas road test.

Design and engineering 

Buy a ‘ticket to Ryde’ in Southsea and you’ll walk through a waiting area and onto a concrete pad, so things feel more like an old airport departure lounge than a ferry terminal. And that’s fitting, because a hovercraft owes as much to the aerospace industry as it does to marine engineering. For the first few decades of the machine’s existence, operations were even governed by the Civil Aviation Authority rather than maritime authorities. Well, it does fly, after all, albeit at quite a low altitude. 

The hovercraft was conceived by Christopher Cockerell, an engineer who had bought a boat hire company and wondered how to make them go faster. Moving through air is a lot easier than moving through water, so he figured it would be better if you could lift your boat out of the sea. Thus inspired, and using two tin cans and a vacuum cleaner, he proved the concept at home before patenting the idea in 1955 – and in doing so, laid out some principles that still apply today. 

It’s a relatively straightforward idea. There’s a hull, around whose edges sits a rubber skirt – the design of which is key to speed and fuel efficiency. Large fans suck air from outside the skirt and push it into it. That fills the skirt with air and the pressure lifts the hull from the ground: the more air you push, the higher the hull gets. At which point, as you’ll know if you’ve played air hockey in a seaside arcade, it’s easier to set an object moving. 

Different-sized hovercraft have different kinds and types of fans. Small leisure, rescue or race craft might have a single fan on the back, to both push the craft forward and channel air, via a duct, into the skirt. Huge American military hovercraft have four gas turbines driving skirt fans, along with moveable thrusters and rear props.

The 12000TD sits somewhere between those two extremes. It has an aluminium hull, which is flat underneath and 5mm thick. Overall, the craft is 22m long (23.7m to the edge of the skirts) and nearly 13m wide. It has two MAN V12 diesel engines mounted longitudinally and sitting side by side at the rear, driving four fans between them, by belt, with no clutches. Two fans pull air into the skirt, with fixed blades, so the higher the engine revs, the greater the amount of air that goes into it. At a cruise, the hull is between 1.5m and 1.8m from the surface. 

Also at the back is a pair of five-blade variable-pitch props, 3.5m in diameter and made from wood but with nickel and rubber on their leading edges. Each can be set to neutral thrust, forwards, backwards or anywhere in between, for low-speed manoeuvres. Behind those are rudders that, in normal forward running, steer the craft. 

And that, bar some finer trim and handling details, is pretty much it. One benefit is that, compared with a conventional boat, a hovercraft is really fast, as Cockerell hoped it would be. The second, though, is that a hovercraft can travel across land, too, which is a huge boon on the approach to somewhere like the Isle of Wight, where there’s a very shallow sea and a long stretch of sand at low tide – meaning regular boats need to take to a pier or have a harbour dug out for them. Our test boat, the Solent Flyer, can take 78 passengers directly to a beach.

Interior

The 12000TD is compact by most passenger boat standards but still imposing as you walk to it from the terminal building. Two passenger doors swing upwards at the front, with steps on one side and a ramp on the other, arcing to the ground over lowered sections of skirt. 

There are two aisles inside, with large, comfortable chairs (no seat belts) in a two-four-two formation across the airy cabin. There are big windows, but they don’t open. Behind the passenger compartment are life vest stores and access to the two separate engine compartments. 

At the front, between the aisles, is an area for a wheelchair and/ or luggage, a stretcher, bicycles and mail sacks. Hovertravel has had a Royal Mail contract since 1978 and carries time- and temperature-sensitive medicine to the Isle of Wight. During the pandemic, Hovertravel became a patient transport vehicle – it’s the fastest way to link mainland and island hospitals. A crew collecting a patient can be away from their ambulance for as little as 40 minutes, and in the past two years more than 500 patients have travelled to hospital by hovercraft. 

Behind the storage area is a six-rung ladder that takes you up to a four-seat wheelhouse, with a seat either side of the floor access hatch and two more up front. 

The one to the front right is for the pilot and has all of the vehicle controls; the left chair is typically used by a navigator. In effect, though, one person flies it: in our case, Steve Attrill, Hovertravel’s head of marine operations. 

You get a good view from up here. If you think Land Rover’s ‘command driving position’ gives a decent look out over things, you should try this – as long as the windows are clean. If you’ve driven a car in winter, you know what a pain road salt can be, but here’s a machine that not only operates in salt water but actively enjoys spraying it up, along with a little sand and dust. Windscreen washers and wipers are vital. 

Ahead of the pilot is a raft of screens and displays, from a radar through to fire control systems and engine rev counters (see the main image on the left for more details). Then there are the flight controls. To the pilot’s left, the red-topped pair of levers control the pitch of the propellers – as shown, they are roughly in a neutral position when the craft is set down. The blacktopped pair are the throttles, again wound back to zero here with the Flyer switched off. 

The rudders can be controlled two different ways, but each does the same thing. There’s an aluminium bar on the floor, which is Attrill’s preferred way to steer the craft “because it leaves a hand free”, but some pilots prefer to use the joystick to their right. Either way, in what could be a useful lesson to automotive designers sticking everything on a touchscreen, there’s an invaluable number of big, clear physical buttons abounding in the 12000TD’s wheelhouse.

Handling and performance 

You can tell the 12000TD is quick because the pilots who operate it have to get a Fast Type Rating in order to sit at the controls. Nonetheless, Attrill calls it a “relatively low-powered” machine, despite its two 24-litre V12 diesels, each making 1063bhp. As crucial as the amount of power, though, is the way the skirt is designed, to allow it to flow over the water while letting air escape in the right places. The skirt, says Attrill, “is the most important part of the raft”. 

He starts the engines to a 750rpm idle, with the craft starting to lift off at around 1000rpm. We’ll come onto the finer points of handling in a moment, but the craft gently rotates into the water, and we’re away. 

Maximum lift, or ‘full hover’, happens at 1800rpm, which seems pretty efficient given that lift only accounts for one-third of the engines’ power and the hovercraft can weigh in excess of 45 tonnes – 33,500kg on its own, with a payload of up to 12,000kg. 

That leaves two-thirds of power for propulsion. In good conditions, this means up to 45 knots – or 52mph in land terms. 

To achieve that means trimming. There are 1700 litres of water ballast on board, with a small joystick next to the rudder stick for moving it around. Attrill won’t have seen where passengers are sitting, so altering the weight distribution will take a few minutes of fine tuning before he’s happy.

Then there’s ‘the hump’ to get over, a variant of wave drag. At low speeds, the craft sits in a depression in the water caused by the downward pressure of the air that gives it lift, so it travels ‘sub-hump’. As speed increases so does the drag from it, until you start to leave it behind. That speed, in the 12000TD, is around 13kts (15mph). The pilot will run the craft level to balance out that drag, but beyond ‘the hump’, water is pumped rearwards to give the craft a 1-1.5deg upward pitch where it likes to accelerate. 

From the passenger seat it’s hard to detect this happening, but the engine torque output dials show it. At low craft speeds the engines are giving 98% of maximum torque, but as speed through the prop increases that drops towards 93%, and at the 31.4kts (36mph) cruise we settled into on a calm, sunny day, that had reduced to 90%. Propeller blades run just 15mm from the ducts, which reduces noise and, like the winglets of an aircraft, also increases efficiency. 

The craft can and will run faster, but not by much. “You’ll rarely see us above 40kts [46mph],” says Attrill. This is because Hovertravel runs to a timetable that there’s no need to beat, and the craft gets thirstier the faster you go. But given the chance, the 12000TD would exceed its 45kts stated top speed. By how much, we don’t know, although it would be a lot of fun finding out. A tailwind obviously helps, as do calm seas – in waves above 1.5m, the Flyers don’t fly, although this affects less than 4% of crossings a year. 

Certainly, conditions on our October test day couldn’t have been better, especially given that it’s the worst month for storms and cancellations. Even so, Attrill is making constant adjustments to our direction. The big rudders, four on each side, are angled 17deg from vertical, which helps create some roll, which increases drag on the inside to help the craft turn. 

“It’s naturally directionally unstable,” says Attrill, “which is one of the reasons why we don’t have an autopilot. Much of what we do is anticipation. The craft is one big weather vane and won’t go for any length of time in a straight line.” 

It basically amounts to one big, long drift, as far as we can tell. Which only adds to the appeal.

Buying and owning 

A hovercraft’s unique abilities makes it the only choice in some circumstances. The military and rescuers such as the RNLI use them because they can operate on sea and sand – the RNLI has a fleet as the only way to get to people who find themselves stranded on beaches or mudflats – while conservation organisations like their very light footprint across delicate terrain. 

But like most fun, fast things, they’re expensive to run. A 12000TD costs around £5million and at full whack use 170 litres of fuel an hour, perhaps 150 with a tailwind. That’s not much less than the 200 litres per hour of an RAF Chinook (last year’s Christmas road test). 

It’s unbeatable in the right place, though. Hence alongside those specialist operations, there’s a summer passenger and freight service in Canada to a community that uses an ice road in winter. There is a service between Russia and China, where the river can freeze and limit boat travel, while a Japanese operator has ordered three Griffons for a regular service to Oita airport. Or if you fancy a used one, the old Isle of Wight hovercraft is available, yours for £3m. If our numbers come up, you’ll have to get behind us in the queue.

Verdict

There’s no reason that the Christmas road test should have a different set of criteria from those of the regular road test – how fit, we wonder, is a product for its purpose? – and assign the rating from there. And here it’s bang on. Five stars.

If you want to cross a stretch of difficult and often changing terrain, at speed, your answer is either this, a helicopter or to go a different way entirely. Here, you can do it in comfort, reliably and at a relatively affordable cost – a day return is £28, while season, resident and concession tickets are cheaper again. 

The hovercraft will remain a slightly niche way to travel, because it is cheaper to go more slowly. But in a particular set of circumstances, this is the only way: a British-designed, eccentric but exotic way, and one that has settled into south-coast life in such an inveterate way that you’ll find people commuting to work and college on it, sitting alongside those who have come from the other side of the world to tick ‘travel by hovercraft’ off their bucket list. We loved it. Last word to Hovertravel’s Steve Attrill: “There should be more hovercraft in the world,” he says. We couldn’t agree more

Road test rivals

Griffon Hoverwork H-Class Rescue: The RNLI’s H-Class hovercraft is a modified Type 470TD designed and built, like the 12000TD, by Griffon. It weighs around 3.86 tonnes and can hit 26kts. The H-Class is powered by Volkswagen diesel engines and can carry up to 10 people. The RNLI has seven in service.

Neoteric Hovertrek: An American maker of small hovercraft for commercial or rescue use, or just for fun. Has a 65bhp two-stroke engine and can do up to 45 knots on smooth ice. Neoteric has been in business for more than 50 years. Cost around £40k assembled or cheaper supplied as a kit.