Dredging the harbour into shape
DURBAN’S harbour master, Captain Alex Miya, has reinstated a number of berths in the port back to their original permissible draughts. This follows Transnet National Ports Authority’s response to criticism that dredging had failed to address shallow spots exacerbated by the size of much larger ships now calling at the port.
A period of concentrated dredging of certain berths has since redressed the situation.
“The vessels calling at our ports have got bigger and therefore require deeper draughts,” said Durban port manager Moshe Motlohi.
“But they also cause challenges for ports because of the manner in which they more aggressively displace material from the sea bed, thus causing shallow spots.”
He confirmed reports in the media that shallower berths had cut into the vessel payloads of ship owners because it meant they could not sail into the port with their vessels fully laden and had to wait for high tide to sail or to berth.
After concentrated dredging alongside, four container berths out of eight at the Durban Container Terminal, namely 107, 200, 202 and 205, have now been called back to their original permissible draught of 12.2 metres.
Berth P at the Point Terminal, Berth MW 9 at Maydon Wharf Terminal and bulk Berth BCA 4 in the Island View precinct have also been called back to their permissible draughts of 10.3m, 9.3m and 10m respectively.
“We are also expecting engineering sounding results that are likely to indicate more berths will be called back to their permissible draughts,” said Motlohi.
He explained that ultimately the safety of vessels had to take priority, which was why the harbour master had taken the safety precaution of reviewing the permissible draughts of some berths this year.
The permissible draught is the vertical distance between the sea bottom and the lowest part of the ship’s underside, otherwise known as the under-keel clearance. In Durban a 600mm clearance is allowed to minimise the chance of the vessel running aground in that area.
The dredging fleet has pursued various interventions to address the issue of diminishing draughts. The authority says it is continuing with maintenance dredging and is pushing forward its R2-billion dredging fleet replacement programme.
While the plough tug Impisi continues to dredge in the port, the short-term plan is for the grab hopper dredger Italeni to continue to dredge along the berth pockets of Durban Container Terminal.
Italeni, which was previously intended to dredge in the other ports, will instead remain in Durban until the port takes delivery of a hired dredger dedicated to Durban’s dredging needs.
Suction hopper
The port authority will also be taking delivery of its new suction hopper dredger, named Ilembe, in December 2015. The new 5 500 m³ capacity dredger – the biggest yet in the fleet – will arrive in Durban in January. Ilembe will be used for dredging larger areas, such as the entrance channels.
The port authority also has access to another of its suction cutter hopper dredgers, Isandlwana, which entered service in Durban in December 2010.
The port authority has also received approval to build another new grab hopper dredger which will be dedicated to the Durban port. This should be delivered by the end of 2016.
The port authority’s long-term intervention is to deepen and lengthen the container and multipurpose berths to cater for the bigger vessels now calling at the port.
This project is expected to begin in 2016 at the container terminal, although it is already under way at Maydon Wharf.
Lengthening of the berths on the North Quay of Durban Container Terminal will allow the port of Durban to berth three big container vessels, against the two it is currently accommodating. This, says Transnet, will immediately reduce the number of vessels waiting at anchorage, thereby improving port turnaround time.
The other benefit is that the port will cease to be a tidal one, so that berthing and sailing will no longer depend on high tide. This will optimise the capacity of the port and improve the total vessel stay in South African waters.
The challenges presented by the larger ships calling at ports is a global phenomenon, as highlighted in a recent report by the International Transport Forum, which said “mega-containerships contribute to congestion and add to the need for costly infrastructure upgrades.