Projects

de Neus - Balancing Act

She’s unique, is now working for the Port of Antwerp and BERT VISSER had a date to meet her...

She’s called De Neus and Raamsdonksveer- based builders Shipyard De Donge call her a ‘balance dredger’ because of her hydraulicallydriven balance grab crane. De Neus was handed over to Antwerp Port Authority (APA) a couple of months back, the latest in a line of vessels that have dredged the docks since 1870, when the city bought a steam-driven bucket dredger to carry out maintenance work. Antwerp continued to buy bucket dredgers and by the 1960s owned three such vessels – two of them still steam driven. Today, one’s been scrapped and the other converted to diesel-hydraulic power. The third, called B4, was originally diesel-electric powered and when built in 1929 was probably the first (or maybe second) of her type in the world. And, complete with her original Smit Slikkerveer engines and 900-litre buckets, she still operates in the port today.

PROGRESS
Port extension projects during the 1970s saw Antwerp building larger, deeper docks with depths up to 18m and the APA had to invest in new dredging equipment:

• The bucket dredger B1, with a 700- litre bucket capacity and a maximum dredging depth of 22m, and
• In 1980, a new split-type, 1,500m3 trailing suction hopper dredger (TSHD), Sinjoor I.

Over the last 20 years, the port’s four dredgers have carried out the majority of Antwerp’s maintenance dredging – about 500,000 tons (dry material) every year. They’re supported by several 650m3 barges, a barge unloading dredger, a cutter suction dredger and a floating crane, the latter mainly used to remove large objects found near quaysides that could hinder normal dredging activities.

RESEARCH & DEVELOPMENT
In 1999, the APA carried out a study of its dredging activities and dredging fleet with the aim of optimizing operations. And that threw up the need for a new, high-performance vessel capable of dredging at least 1,100 tonnes of silt per hour, with a dredging depth of 18m and able to operate with great accuracy. The latter point was considered vital by the port authority because of the risk of destabilizing existing quay structures by dredging too deep. And a survey of other European ports showed that in most cases backhoe dredgers were deployed for this type of work. But Antwerp’s specific requirements – the combination of a high production rate with a dredging depth of 18m – meant such a vessel would need an extremely large, heavy backhoe crane fitted with a very small bucket – 3m3 maximum. The APA briefly considered using a rope grab crane, but dismissed the idea as it wouldn’t meet the accuracy requirement. And then someone suggested the balance crane principle... It’s a proven technology, used for both port and shore-based applications – mainly at scrap terminals – but had never been used for dredging. Why? Because such a crane can’t exert any real penetration force into compacted river or seabed material. But for Antwerp, this disadvantage simply didn’t matter as maintenance work there means dredging in soft soils, mostly silt. Further study of the concept proved to APA that a balance dredger would be the ideal solution: such a vessel could be fitted out with a relatively large grab of 15m3, enabling it to comfortably reach the required 1,100 tonnes of silt per hour production rate. The dredger can use such a large grab because the crane’s boom and stick are counterbalanced in any position when dredging, thus only the weight of the grab itself and its content have to be lifted.

OUT TO TENDER
In early 2002 tenders went to several shipyards, with the contract awarded to Shipyard De Donge that August, the yard proposing to use a balance crane from French manufacturers Seram. Not only did De Donge submit a competitive price, but the yard also came up with an advantageous alternative technical solution... The APA’s original idea was for a diesel-electrical dredger, but De Donge suggested diesel-hydraulics instead, a configuration offering:

• More efficient power transmission
• Simpler construction and less noise as no separate power source is needed to drive the crane, and
• Overall, a more economical vessel.

FINALLY...
Not only has the APA a unique vessel in De Neus, but one that’s perfectly suited to fulfil a major part of the port’s dredging needs. As a result, bucket dredger B3’s likely to be decommissioned in the near future, while the B4 will almost certainly be taken out of service too, though held in reserve. In short, De Neus represents a major step in the modernization of Antwerp’s dredging fleet and a benchmark for other ports with similar dredging needs.

Tech Specs
DE NEUS is a self-propelled pontoon, 53m long and 19m wide

• Type 880 Balance Crane – supplied by French builder Seram, it weighs nearly 300 tons and is the largest of its type ever built by the firm. It has a 26.5m boom, a 17m stick and can dredge to a depth of 18m
• Main Power Plant – one ABC type 6 DZC- 750 1,065kW diesel engine that provides all the energy needed aboard – propulsion, crane operation and spud-lifting
• Spuds – three, each 24m long, which means De Neus doesn’t need to anchor while dredging, causing minimal obstruction to port vessel traffic.
• Spud Winches – mounted below deck in three separate winch rooms, avoiding the need to have cumbersome (and potentially dangerous) cables on deck
• Dredging Instrumentation – supplied by Seatools and giving De Neus centimetre dredging accuracy.

The origin of this story is DPC magazine June 2004

More info at www.dpcmagazine.com