HOVERING with INTENT
Most of us pass through Auckland Airport at some stage in our lives, where giant airliners line up on a runway sticking into the Manukau Harbour like an extended forefinger. Few think about the people tasked with picking up survivors if it all goes wrong.
Depending on the state of the tide, the D runway is surrounded by a quagmire of mud and sand flats, thinly disguised, at high tide, by turbid brown water. But every year more than two million people pass overhead; sitting in that parlous state between being aloft and aground.
Few people notice the cluster of buildings on the foreshore or, if they do, don’t give them a thought, but it’s headquarters for the 60 or so personnel of the Airport Emergency Services (AES) who maintain a 24/7 watch on operations.
The airport firefighters are, like their urban counterparts, constantly on alert for potential danger and highly trained to cope with it. But, in line with the specialised nature of their location, they have a two extra tools.
These are the two lime-green Griffon hovercraft slumped on deflated air skirts in the fenced-off yard on the harbour shore.
“This one [H1] is 25 years old,” says senior firefighter and hovercraft trainer, Richard Gowdy. Its lime fuselage looks like new.
“One of the advantages hovercrafts have over helicopters is that you don’t need specialist technicians to maintain them.
He unlatches an aluminium cover. “Look – a plain old Deutz air-cooled V8 diesel – just about any mechanicallyminded person can look after it.”
A belt-driven compressor off the front of the engine “generates the volume of lift-air that’s maintained by the flexible skirt at a higher pressure than the ambient atmospheric pressure,” the Griffon website explains. “They can travel over almost any non-porous surface – ice, debris, rock, sand.”
Another belt takes power from the back of the engine to drive the two-metre diameter propeller and an electrohydraulic pump pushes the hydraulic oil used to adjust propeller pitch. “The default position is full pitch – so you always have enough drive to get you back to home base if anything fails,” says Richard.
Not much of this is new technology – Sir Christopher Cockerell conceived the idea over 50 years ago. Hovercraft have been used for years to supply far-flung outposts in the Canadian Arctic over thin ice during their frozen winters.
“She’s saved a few lives, this old girl,” Richard pats the aluminium hull affectionately. The AES hovercraft are called on by police, Coastguard and SAR authorities in Manukau Harbour and have rescued kayakers, paddle boarders, distressed fishers and others.
“They’re perfect for rescue work,” he explains. “You can go right up to a person or vessel, deflate the skirts and settle beside them like any boat with extra low freeboard. They don’t leave any wake or wash – and you can go almost anywhere. Sometimes we take one down to Huia for a cup of coffee or a feed of fish and chips – just run it up on the beach and walk across the road.”
Underneath, the 2mm marine alloy hull plating is
slightly concave with buoyancy tanks running down each side to stiffen the structure and provide fastening points for the rubber skirts.
Richard ushers us aboard H2, a five-year old Griffon 2000TD, powered by a 440hp, liquid-cooled Deutz V6 diesel, and distributes lifejackets with his safety briefing. “If we turn over,” he points out, “we won’t be able to get out of the gullwing doors – so take this fire axe and smash the windows.”
The hovercraft are under Maritime New Zealand survey for 15 passengers but there are six 30-passenger life rafts fastened around the side decks and, “if we had to – we’d load them to the max,” says Richard. “If a plane dumped in the mud or shallow water – our role would be to transfer survivors to the boats waiting out in deep water.”
Each shift of airport firefighters has four skippers who hold
Restricted Limits Launch Master (RLL) tickets. They carry a minimum crew of three; helmsman, skipper and trainee/ deckhand. They aim for a five-minute deployment deadline from an alarm being sounded to on-the-water readiness.
It’s a cold, breezy day and the latte- coloured water looks most uninviting. “Our operating parameters are 20 knots – gusting 30 – of wind. We call the control tower and they tell us what we’ve got.”
Any engine or belt noise from the Deutz is drowned out by propeller roar as the bags inflate and the hovercraft jerkily rises like a camel groaning to its feet. It glides towards the water. Well – where the water should be at high tide – and barrels down the launching ramp, slightly down by the nose with a sensation that is half floating, half flying.
“One difference from a boat is these foot pedals,” Richard points out. “They control the skirt matrix by pushing or pulling a stainless rod which alters the shape of the skirts to enable better handling and cornering. And, of course, you have to alter propeller pitch in sync with whatever manoeuvre you want to do.”
They can travel over almost any nonporous surface – ice, debris, rock, sand.”
Three small rudders are mounted side by side in the propeller wash and enable the hovercraft to virtually spin on its axis at speed. With no boat in the water, or friction on the skirts, the hovercraft rotates effortlessly, the panorama flashing past the windows is the only indication that we’re in a two-tonne spinning top.
The Griffon website cautions against operating the hovercraft on steep slopes. “All hovercraft are susceptible to side-slipping,” it says understatedly.
“Driving them is seat of the pants stuff – some people get the feel for it quite quickly – others never do. These things are all about centre of gravity – you have to be mindful of it all the time – it’s all about feel,” says Richard.
Any of the airport crash responders who show interest – and a degree of competency – can ask to be trained as hovercraft operators.
Another point of difference from a conventional vessel is the ballast/ fuel tanks which hold 440 litres of fuel at either end of the boat – sorry, hovercraft. A pump transfers the fuel from tank to tank in seconds through 50mm pipework. Counter-intuitively, says Richard, they go better downwind when the weight is in the forward tank.
At about 20-25 knots we scoot across the sand bars and over the channels, ignoring markers and buoys, like schoolboys splashing through puddles after school. The wheelhouse windows are quickly covered in a smear of muddy water being pushed around by the three wipers.
In operational mode – the skipper would sit in the right-hand seat to keep an eye on the radar and plotter.
The launching ramp is dead downwind. “That’s about the worst angle of attack for a hovercraft – the wind up your backside pushes you all over the place.” Gauges flicker and he hits switches to transfer ballast, his feet firmly pressuring the skirt control pedals. The ramp lines up with the craft’s blunt nose and we run straight up it to settle in the car park. Easy as that.
At 1800rpm, the Deutz uses about 45 litres per hour of fuel. Consumption climbs to 75 litres at 2000 rpm and doubles to 90 litres at 2100 rpm. “We try to run them at about 1500rpm which is economical cruising and less drag on the skirts,” says Richard.
“The skirts last for years – but we only get 4-6 months out of the fingers (the rubberised strips on the underside of the skirts that make contact with the ground).”
Operational speed over water is 35 knots, or 15 knots on firm ground, and they can carry a 2200kg payload. “They’re the perfect tool for the job really,” Richard says.
Ready and waiting.
BELOW H1 is surveyed for 15 passengers but she carries six 30-person life rafts.
BOTTOM The operational end of the hovercraft, and opposite, right, the 440hp Deutz V6 diesel engine.
LEFT Plenty of space to accommodate passengers unlucky enough to end up in the drink. BELOW Propulsion comes from a fivebladed, two-metre propeller.