One kilometre off the coast of Newcastle, the crew of the dredging vessel David Allan flicks a switch, releasing a hydraulic lock that allows the ship's hull to split in two.

Key points: The Port of Newcastle dredger needs to maintain a channel depth of 15.2 metres from its breakwalls to coal shipping berths

The Port of Newcastle dredger needs to maintain a channel depth of 15.2 metres from its breakwalls to coal shipping berths The first commercial shipment from Newcastle was 220 years ago, with dredging required for the past 160 years

The first commercial shipment from Newcastle was 220 years ago, with dredging required for the past 160 years The David Allan does around 10 trips per day, every day of the year

As the 70-metre hull cracks open, 1,100 cubic metres of mud, sand, rocks and water is dumped into a one kilometre square area of waters known as 'the spoil grounds'.

In one form or another it is a process that has been operating continuously at the Port of Newcastle for 160 years.

Last month's 160th anniversary came at the same time as the port marks 220 years of operation, starting with the first commercial shipment from Newcastle in 1799.

As the spoil empties, the vessel turns around and returns to the mouth of the Hunter River to continue dredging — a process that continues 12 hours a day, seven days a week.

Silt and sediment from the sea bed of Newcastle Harbour pours into the hopper on the dredger David Allan. ( ABC Newcastle: Anthony Scully )

Dredge engineer Dana Crampton reflects on the marvel of naval engineering that is the David Allan.

"You're meant to keep boats together to stay afloat, and this one just splits in two and dumps the whole lot," she said.

"It's really quite unique in how it operates."

In a 12-hour shift the vessel might make the journey out to sea 10 times, a fact that might escape most Novocastrians on shore.

"People see us going in and out of the harbour, and probably half of Newcastle don't know what we do," Ms Crampton said.

"It's like 'oh, is that what that boat does?'"

Dana Crampton says it is unique how the boat stays afloat when it is designed to split in half. ( ABC Newcastle: Anthony Scully )

Nine kilometres of channels need constant attention

The location of the dredger changes constantly, depending on which part of the port's nine kilometres of channels needs attention.

According to the Port of Newcastle, the dredge needs to maintain a channel depth of 15.2 metres, from the breakwalls to the Kooragang 10 berth in the river's South Arm.

The David Allan operates 12 hours a day, every day of the year, to maintain a depth of 15.2m throughout the port. ( ABC Newcastle: Anthony Scully )

During the infamous Pasha Bulker storm in 2007, there was so much sediment the channel lost almost a metre in depth which took approximately six months of dredging to clear.

The importance of maintaining safe keel clearance for vessels using the channels is not lost on the crew, which is licensed to move 650,000 cubic metres of silt and sand each year.

"Basically, if we're not here keeping the harbour clean they can't come in and out, which closes the port down," said crew member Mick Crabb.

"We play a pretty important role, I'd say, not only for the Port of Newcastle but for the coffers of Australia."

Crew member Mick Crabb says the drag head, pictured, at the end of the dredge pipe works like a vacuum cleaner. ( ABC Newcastle: Anthony Scully )

Like Groundhog Day, but in a good way

On the David Allan's bridge, dredge master Tim Hooper pointed to a map on a computer screen divided into a grid representing an area the size of several football fields.

"That's an area where the government's given us approval to place the spoil material," he said.

Mr Hooper points to the location of spoil grounds, where the government has allowed the dumping of mud, sand, rocks and water from the channels. ( ABC Newcastle: Anthony Scully )

"We've got a dumping management plan. We then take the material out there to the spoil ground, monitor our position and record where we've placed the material."

Although the repetitive nature of the work can sometimes feel like Groundhog Day, Mr Hooper said 'boring is good'.

"There's different flavours of exciting," he said.

"The most interesting parts of the job, I find, are the problem solving and adapting to the dynamic situations that come up all the time.

"I was away at sea for 15 years before this and I now get to go home and see my kids every night. So that's the bit I like."