Electric converted LandCruiser attempts to drive under Darwin Harbour – 7 kilometres in length, and up to 30 metres deep!

By Toby Hagon 11 Min Read

It’s one thing bolting on a snorkel to making wading across a river that little bit easier. It’s another altogether engineering an old Toyota LandCruiser to drive for seven kilometres under Darwin Harbour. At depths of up to 30 metres.

That’s the challenge a bunch of engineers, enthusiasts and passionate car blokes have taken on with an ambitious attempt to set a few world records.

But first…

First, let’s start waaaaaay back at the start. 40 years ago someone attempted the same crossing in the same model FJ40 LandCruiser … only to have it fail.

“I heard this story growing up,” explains Glen Summers, an electrical engineer who’s also worked on solar car races and relishes a challenge.


“We’ve all worked on whacky projects all over the world,” he says of the team that was assembled.

It’s what drew him into this project, which was kickstarted by Tom Lawrence, who grew up in Darwin.

The team grew to include a diverse mix of talents from not only across the country but also across the globe.

Three of the team are from San Francisco. Where they worked as electrical engineers in Silicon Valley. One formerly worked for Tesla. And has injected some of those EV learnings into a car that looks like it’s seen plenty of rough roads.

Another is Luke Purdy, who presents a reality TV show called Aussie Salvage Squad. He’s used to unusual requests and giant challenges. Which is handy because the underwater FJ40 certainly created that.

Describing it as “the opportunity of a lifetime” and “an engineering challenge” he says the FJ is like three projects in one.

“First we had to build an electric car. Then build an underwater car and restore a LandCruiser,” says Purdy.

As well as keeping water out of key components, he says the team was busy “understanding the theory of what happens with pressure and what happens to oxygen underwater”.


That’s one reason the 37-inch Maxxis tyres are filled with water: to cope with the pressure of being 30 metres underwater. Each now weighs about 180kg.

The FJ

The short wheelbase FJ40 ute was bought for $5000 as an unfinished project. It’s got some surface rust and the obligatory faded paint. And it looks like it’s dealt with its fair share of Aussie dust, corrugations, rocks and sand over the years.

It’ll soon be dealing with a lot more sand…

It’s also picked up a nickname: Mudcrab.

“That’s because it’s orange and crawls along the bottom of Darwin Harbour,” says Lawrence.

While its Toyota 2H petrol engine has now been removed, the gearbox and transfer case remain.

An electric motor provides the drive through the standard drive shafts and diffs.

It’s all about keeping it simple.


That was the focus with the LandCruiser.

The Mudcrab FJ40 was designed with one focus in mind: an underwater crossing.

Everything in it has been chosen and engineered for that sole task.

“The car is not made to drive on the road,” says Summers, explaining “we don’t have a battery management system” because “it’s more stuff that can fail”.

A BMS is a standard component of any roadgoing EV to keep an eye on cells, voltages and other key electric components. But the FJ40 team is instead monitoring charging externally when the car is on land to ensure the batteries are up to the task.

Powering up

The battery pack measures 32kWh, about half that of most EVs.

But it only has to travel a bit over seven kilometres.

That said, they’ll be tough kilometres.

Water is a lot harder to push out of the way than air, so the electric motor will be utilising much of its torque to keep moving.

The car will be travelling at 1-2km/h, a glacial pace, but plenty in the dense flow of H20.


From Datsun, with love

The electric motor in the FJ is an off-the-shelf NetGain HyPer9 unit commonly used in EV conversions.

So much so that it was initially to be installed in an old Datsun.

The owner then changed their mind and decided to sell it before it had even been used.

“We got it second hand unused,” says Lawrence.

The motor makes 88kW and 162 pound-feet of torque (about 220Nm). They’re modest numbers, but more than enough in an old LandCruiser, especially once you consider the torque is available from zero rpm.

The motor has been mounted on the front of the gearbox. It’s protected from the elements with some innovative engineering.

“We basically put a garbage tin over the top of it and saturated it with silicon oil,” says Purdy of the efforts to ensure the electrons keep flowing.

Back and forth

Because an electric motor can run forward or backwards, reverse gear in the gearbox is superfluous. To change the direction of travel, the driver can just change the rotation of the electric motor with a switch.

That’s part of the reason the car now runs only two pedals, with the clutch pedal (and the clutch itself) removed.

While it could have remained in the car, the team saw it as one extra component that could cause an issue or leak fluid when they didn’t need it to.

Water out and in

The team worked hard to ensure critical components – the battery and electric motor, for example – are sealed from water.

At the same time, they identified components that could deal with some water ingress.

“The transmission and diffs can handle water,” says Purdy, who knows 4x4s backwards and has seen the punishment OEM components can deal with. “So we’ve gone for an open system because it’s easier.”

The team instead filled many drive components with food-grade grease, which not only lubricates but also keeps sea water away from metal components.

The biodegradable grease is used in food preparation and won’t harm the ocean if some seeps out. Its thickness also nicely prepares it for the slow speed drive.

High pressure

It’s one thing keeping water out of components that will fail if they come into contact with it.

It’s another dealing with the pressure of hundreds of tonnes of water from above.

The build team worked tirelessly to ensure the FJ is ready for the intense pressure.

The entire car and its components will be under 60psi of pressure at a depth of 30 metres.

“Our components internally are kept slightly higher than the outside ocean pressure,” says Summers of the efforts gone to preparing for all that pressure.

He says on land those key components are a few PSI above the ambient pressure and that is increased when the car descends. Two hydraulic pressure compensator bladders have been added to stabilise the pressure throughout the system.

The drive team

The next phase of the FJ40 development is to hit the road – or sand.

And it’s more divers rather than drivers that will pilot to underwater FJ40.

Each has to be proficient in deep water diving and wear appropriate safety equipment.

There are about 30 of them in all, because no one can spend the entire time underwater due to the pressure.

All are doing it to be part of the crazy adventure that is hoped to snag a few world records.

They won’t use the Guinness World Record tag, though, because there were significant costs involved with that.

And while the team had to speak to the Darwin port authority and harbour master, it says that because it’s not a commercial venture “you don’t need permits for aquatic activities”, something that meant a little less red tape for the underwater run.

Test run

Earlier this week the Mudcrab went for an underwater test run at Casuarina Beach in Darwin to check its systems and validate the months of intense work that have gone into it.

Lawrence says “it couldn’t have gone any better”.

But there’s more to be done ahead of its world record attempt this weekend.

As well as final checks the team is repainting the car, with a rescue life ring inspiring the theme.

“Imagine Aquaman was building a 40-Series and he had to make 1000 cars, what would that factory build?” says Lawrence of the new orange and white colour scheme.

“We want to make it look like it’s just come out of the factory.”

All of which will be quite the sight if – the team says “when” – the humble FJ40 emerges from the ocean after seven arduous underwater kilometres.

The ambitious attempt takes place this Saturday, July 29.


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