In the shallow end

tidal ports beckoning in ships along their fairway sometimes have their fingers crossed Tidal ports beckoning in ships along their fairway sometimes have their fingers crossed
Industry Database

Tackling depth blackspots can be a key to increased productivity, explains Stevie Knight

Some ports are born with restricted depth, others have it thrust upon them. Take Marsden Point, for example. This refinery outlet had a good trade going when suddenly, after 30 years of apparently safe operation, two oil tanker groundings occurred within three months of each other, resulting in an environmental calamity, a media circus and a lot of questions.

The port’s 14.7m depth had been suddenly and significantly marked down, effectively barring the big tankers. The resulting hit was large enough to reach beyond the port, affecting New Zealand’s whole economy.

However, although the Marsden Point issue was probably one of the most notable, it’s a potential that affects many ports, box and bulk alike.

Peter O’Brien, chief executive of OMC International, says that tidal ports beckoning in ships along their fairway sometimes have their fingers crossed. He explains it’s a fact of life that the static rules that govern the depth of keel that should be able to get across their doorstep “are fine 95% of the time, marginal 4% and downright dangerous 1% of the time”. He adds: “The problem is, you don’t know which time it’s going to be an issue.”

Plus, he adds that if there’s a silty or sandy bottom neither the port nor crew will necessarily even know that the vessel has even grounded, with damage becoming apparent later.

Mr O’Brien explains the issues: “There’s a lot that these static rules simply can’t take in. Beyond wind, waves and swell impact there’s the pace of the ship; pilots who may be worried that they won’t reach certain waypoints before losing the tide will often go a little faster, causing the ship to heel over or squat – the hull working like an upside down aeroplane wing.”


On the spot

So, a responsive system that not only takes into account the fairway and environmental condition but also the vessel itself is going to give much more accurate results. This is where OMC’s Dynamic Under Keel Clearance (DUKC) system can help, as it gives both the port and bridge (via screen/web access) a good picture of what is coming up under the hull – and what will be showing up later. This application helped restore confidence in the Marsden Point operation, allowing the tankers back in.

Jonathon Pearce, previously a pilot at the Port of Taranaki, New Zealand (and now OMCs pilotage adviser) has had firsthand experience of this system doing rather more than act as a ‘safety alarm’, and actually helping to open up trade. He explains: “Energy politics lost Taranaki 4m tonnes of methanol trade virtually overnight. Although Fontera’s milk cargo was on its doorstep, Maersk said it would bring in its ships only if there was a guaranteed 11.2m of draft, and at that moment, Taranaki could only guarantee 10m.”

The port looked at capital dredging alone and in combination with the DUKC system. “It showed us that with minor dredging of berth pockets and high spots in the approach we’d get to our magic figure of 11.2m almost overnight. All in all it reduced our dredging costs by half, nowhere near the price of the system.”

But more impressive was the effect on sailing windows: “One three month period showed up two encounters as dangerous that the static rules would have simply passed. However, on the other side there were around 80 voyages in and out of the port where the rules would have only given a five-hour window but this system showed we could realistically work with 24 hour-a-day sailing.”

Taranaki is not alone. There are quite a number of box ports like Lisbon’s which used to have to keep vessels hanging around outside to comply with risk mitigation measures until they deployed the DUKC system, and bulk ports like Australia’s Dampier have gained quite a bit as the system means they can keep loading up until the last minute, given the wider window.


Southern success

But why is its popularity mostly constrained to the Southern Hemisphere? There could be a number of answers to this. One is the bigger tidal extremes of the Antipodes, although there are enough tidal ports in other regions that might benefit.

Another could be the ‘hot political potato’ effect. One source familiar with the DUKC system said that a more northerly facility that had been pursuing dredging permissions for a number of years “simply didn’t want the introduction of a possible ‘solution’ to confuse the issue and give the environmental pressure groups something to throw back”.

Mr O’Brien himself admits: “People can occasionally get into the habit of thinking in opposition to each other, which means some possible ways forward can be ignored.” Despite this he points out it’s not the only response and some ports are much more positive: “Montreal, on the other hand, is trying to get stakeholders onboard, so it is using the DUKC system to show its real commitment to mitigation measures.”

While there are some clever bits of kit that help ports with issues around depth or morphology, environmental concerns add a whole dimension to the cost/benefit analysis of dredging, not least because environmental tariffs can be steep in sensitive areas, with a much larger compensatory area balancing every square metre of disturbance, explains Paul Morter of BMT Argoss.


Gut feeling

So, while a port may feel the answer is usually not so elusive and may already have a sense of what will work, the fact is that getting the figures nailed down and a realistic compromise worked out is a whole other ball game. Mr Morter says an important aspect of BMT’s Rembrandt simulation is that “it helps put metrics to gut feeling”.

The fact is, it’s not always clear. One Asian port’s realisation that its usual long, winding approach didn’t stand up to new business needs was complicated by the simultaneous realisation that widening an alternative channel was going to hit an area of sensitive flora. “Running the simulation gave an overview of various dredging options that brought together a minimal amount of environmental impact with an acceptable level of navigation safety,” says Mr Morter.

However, it is possibly a less quantifiable benefit that could make the most difference to outcomes. He goes on to explain that a simulation aids transparency, allowing all the stakeholders to get around the table, not just the port authority, ship and tug masters but the environmental groups and residents who are increasingly included in the search for solutions.

“You can take a helicopter view and visualise both a vessel’s progress through a channel and the impact of change on the surrounding area. It helps everyone, marine background or not, to see the challenges and work together toward potential answers."


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