Appeared in DIVER June 2010
Why did no-one think of making a tank-mounted DPV before? John ‘Jetboy' Bantin goes west to try out the Pegasus Thruster on some big wrecks
THE REMOTE CONTROL was gripped firmly between the handle of my big camera housing and my hand. I held the other handle of my camera housing, and looked through the viewfinder. Things didn't look promising.
I had been hoping to try the Pegasus Thruster by sweeping majestically round the wreck of the 155m-long Spiegel Grove off the Florida Keys, but high winds had made diving in the sea impossible.
So we were reduced to immersing ourselves in a Florida creek that had visibility no better than London's Wraysbury Lake, over a weekend when all the trainee divers had been stirring things up.
However, I had come a long way, and with a retreat back to the UK impossible thanks to a plume of volcanic ash over Europe, I was going to make the best of a bad job. I pressed the big Go button and, after a moment's thought, as the electronics checked that everything was technically OK, I was off.
I was travelling silently with no effort on my part, chasing my similarly equipped dive-buddy Dean Vitale through the murk in a bid to get some pictures.
What was unique about our form of transport was that I was totally hands-free, and able to use my camera.
Other diver propulsion vehicles (DPVs) require you either to hold onto them with two hands, or to be towed by a lanyard, steering by rotating the DPV with one hand.
Holding on with two hands can result in tired wrists and biceps, to the extent that some DPVs cannot be said to remove all the effort from making progress under water.
Hands-free, I merely had to turn my torso a little to control my direction of travel. If I wanted to stop, I released the magnetic switch in the remote control and the effect was immediate. I looked where I was going, pressed the button, and that is where I went. It was so easy – it was simple.
IN DEMAND
Dean Vitale conceived the Thruster for use by disabled divers, and he continues to work with Fraser Bathgate and the US Wounded Warriors organisation.
It seems ideal for this application, but others too have caught on to the idea that you can do a lot more work under water if your air consumption is not taken up by the effort of producing leg-power.
The security services have found that they need far less manpower to do the under-hull inspection of ships entering Miami Harbour. The US military is experimenting with some examples.
Dean is getting ready to demo the idea to Seabees (US Navy Construction divers) and other parts of the US Navy.
Woods Hole Oceanographic Institution has purchased units, as have Florida's Department of Transportation bridge-inspection teams.
Even Britain's security services, charged with protecting the 2012 Olympics in London, have noted that they can inspect more underwater structures such as the bridges over the Thames if their divers are equipped with these devices, or, at least, that they can use fewer divers for the job. The future looks bright for the Pegasus Thruster.
THE CONCEPT
I had previously met Dean in the UK at Pinewood Studios, where he was experimenting with using the Thruster with an underwater cameraman in the underwater studio. Since then he has come up with all sorts of ideas for using the Thruster in conjunction with a remotely operated camera.
Pinewood is where we conceived the notion that I could give the DPV a full sea trial for divEr in the Florida Keys.
I first saw a prototype Thruster a couple of years ago with Fraser Bathgate at a DEMA show, but it was not until Dean got the commercial backing of Miami businessman Patrick Gleber that he was able to get the fully developed idea into production.
The concept was to produce a sleek device that could be added to an existing scuba tank and BC and be easily controlled, even by someone with no use of his hands, for example by squeezing the control under the chin.
The remote control at the end of its lead is a key part of the design. Its switch is designed to avoid wear by using the repelling properties caused by the reversed polarity of two magnets.
The motor is developed from a well-known high-torque electric motor normally found in heavy-duty power drills, and as such can take a lot of use.
However, unlike a drill that might be used to attack concrete, all the Thruster's motor has to cope with is the viscosity of water. It should therefore enjoy a long life.
Power is transferred to the propeller via a gearbox with a clutch mechanism that prevents damage should the propeller get fouled.
The 12V ni-mh battery gives enough “current draw” for its application without being unstable, vital when sea water is in the vicinity. As Dean put it: “It gives enough grunt!”
The unit includes sensors that disconnect the motor when the voltage gets low, and there is an automatic clutch release. All circuit boards are laminated in silicone.
OVERALL, THE UNIT GIVES MORE than 15g of thrust. I appreciated this while holding on to Dean's ankle as he dragged me around, giving me the chance to take close-ups of the big whirling propeller and the shroud of his Thruster.
A bracket and camband is used to mount the unit on the tank, low down to allow clearance for the propeller. This is a quick-connect device, and when you're ready to dive, the Thruster simply snaps into place.
After a dive, it can be removed in a moment by pulling a pin and unhitching it, allowing the diver to sit down. It's all very convenient.
The cable of the remote control is connected via a wet connector and, very unusually, the battery-pack can also be connected or disconnected from the drive while still under water. This gives the option of extending the 45-minute duration by changing batteries during the dive.
The battery-pack and powertrain snap together inline to form a torpedo-like shape. In fact the Thruster is remarkably slim when compared even to the most lightweight DPV.
Dean manufactures the whole thing in a small facility in Florida, hand-assembling each part. It's beautifully crafted in anodised aluminium, with a high-impact plastic shroud and prop. Like so many good ideas, the basic concept is so obvious that one wonders why no-one else has thought of it.
Mounting the unit on the tank means that it is not at all intrusive, and if you want to fin without its assistance, you don't notice that it's there.
I found it perfect if I wanted to stop, resort to conventional finning while taking a picture, and then move on.
ON THE WRECKS
After a week of waiting we got lucky, and the weather cleared. Dean was able to take me out in Patrick's 40-knot fishing boat to dive the wrecks of both the Spiegel Grove and the Duane.
It took no time to zip round the whole of the vast Spiegel Grove, formerly a military hovercraft transport ship, even with pauses to take pictures. I didn't go deeper than 32m, but stayed a long time at that depth and found that the nitrox in my 11-litre tank easily lasted the dive.
We startled a couple of giant wreckfish that weren't expecting us to approach so quickly, and hurtled through thick shoals of Atlantic spadefish and pompano jacks.
As we made our way back to our upline, a huge school of silvery barracuda came flooding into the wreck.
It was exceptionally nice to know that the upline was never far away in terms of time. It only needed pressure on the remote control of the Thruster to see us zooming back the way we'd come.
I don't think many people get to see the whole of this wreck on a single tank, and without incurring long deco-stops.
THE DUANE IS A VERY PRETTY WRECK, because it's covered in growth but quite deep. I limited myself to 37m. It was a Coastguard cutter, purposely sunk like the Spiegel Grove, but around 20 years ago. It's full of fish, including a couple more wreckfish and lots of big, toothy barracuda that I found I could approach really closely.
Like the wreckfish, the barracuda aren't used to divers zipping so quickly over to them, and of course it's easy to hold your breath while you're doing it. It's effortless.
The Duane is often swept by strong currents, which this could have led to some anxiety about getting back to the mooring line to which our boat was tethered – but not with a Thruster mounted on my back!
As soon as I wanted to go back, I went – and I really went. Because it was not necessary to shelter against the water flow by being close to the deck of the wreck, I could travel through blue water and complete a slow ascent as I went.
The 45-minute runtime proved very adequate, considering that I didn't run the Thruster while taking pictures.
Of course actual speeds and runtimes vary enormously, depending on the amount of drag. With a wetsuit and single cylinder the Thruster sped me along, but not so quickly as to threaten the watertightness of my camera housing.
I would guess that I was going as fast as I could have been with a Gavin, Farallon or other proper cave-diver's DPV of the sort I have used before.
THE PRODUCT
You can fit one Thruster to twin-tanks or fit twin Thrusters; in which case it's possible to specify counter-rotating propellers to avoid any pronounced torque-effect that might make it easier to turn one way than the other.
With the single unit I noticed no such effect, and found I could go readily in any direction, including downwards.
Because it's hands-free, I could easily pinch my nose to clear my ears as I descended, too. (You must take care not to ascend too quickly with any DPV.)
The whole thing is less than 59cm long, and the widest part, the shroud, is around 22cm in diameter. It weighs 5.5kg in the air and is about 2kg negatively buoyant in sea water.
It comes in a Pelican case with two battery-packs, tank-bracket assembly, tank strap, battery-charger and the remote control with its magnetic switch.
One option that might interest some commercial users is the “surface-supply” umbilical version, which can provide a tethered diver with propulsion to 100m away from the surface.
This newly released assembly will appeal to those involved in ship hull inspections, giving the diver unlimited time to get the job done.
The price for the UK has yet to be fixed, but expect it to be around £3200, so don't expect to see too many in club RIBs.
However, if someone did want to take one aboard such a small boat, it would not be too much of an imposition for fellow-divers – it even fits into a typical tank rack. Show me another DPV that does that!
Visit Pegasus Thruster's website.
