The company also commenced an investment and fleet modernisation programme aimed at having both the best equipment and operational independence. The process has seen the refurbishment of existing plant and investment in newbuildings. A year spent thoroughly and carefully examining the marketplace identified a clear opportunity for Humber Work Boats to equip itself with a large self propelled backhoe dredger capable of working in the 10 to 19m depth range.

Dredged depths of 15m in fairways and alongside are becoming mandatory as major ports compete to accommodate higher capacity, deeper draught VLCCs, bulk carriers and containerships. There is also considerable scope for works in harbours and marinas, where the hard digging and break-out capabilities of a powerful backhoe dredger are much in demand.

There are a number of major and smaller ports within a day's sailing of Humber Work Boats' North Killingholme base, and it is here that the decision to opt for self propulsion comes into play. Most dipper dredgers depend upon towage or even heavy lift for mobilisation and then require dredging support vessels for assistance once on site. A self propelled dredger offers clients considerable efficiencies of both time and money.

For Humber Work Boats, the obvious choice of builder was across the North Sea in the Netherlands. Shipyard De Donge has built a reputation for the innovative design and construction of backhoe dredgers.

Dating to the 1830s, the yard began concentrating on dipper dredgers, floating cranes, self elevating platforms, split barges and spud pontoons in the 1970s.

Humber Work Boats' vessel was delivered last month in time for a blessing service and celebration at North Killingholme.

Christened Pat M in honour of Pat Morton herself, it is the 72nd dipper dredger to leave Shipyard De Donge and all but one of those remain in service. Pat M is unique in being the first self propelled dipper dredger to come from the yard. The vessel is a B-Type Donge Dipperbarge 600, with a length of 44m, a 14m beam and a draught of 2m. It is classed by Bureau Veritas 1-3/3 for self propelled coastal service up to 30 miles offshore, meaning it can cross the Channel for work in continental Europe without tug assistance. Its services will be available in UK and European markets on contract or charter basis.

A Demag - Komatsu PC1400 125 tonne Aquadigger excavator is mounted on a pedestal on the lowered aft deck. The excavator sits on a flexible pedestal and is connected to the heavy excavator deck with special bolts. Power is from a 1,000hp Cummins diesel engine which, in an arrangement developed by Shipyard De Donge, also powers the hydraulics operating the vessel's three 26m long spud legs. The pontoon can be stabilised on the seabed and lifted 80 cm out of the sea to work in a wave height of 1.5m.

Propulsive power is also provided by Cummins. Two 440hp main engines reside in completely seperate engine rooms, each driving a 360º HRP thruster with wheelhouse controls also by HRP. This combination exceeded expectations by powering the vessel at 8.5 knots when it was delivered from the Netherlands.

The thrusters are in a well protected position below the excavator and above bottom level, suggesting the Pat M will be able to tow her own splitbarge for further operational economies. A full house of Cummins power on board is completed by generators of 118kVA and 38kVA.

Precision and efficiency have become bywords in the competitive world of dredging and to achieve them the Pat M has been equipped with the most sophisticated electronic . .

. . controls. Trimble RTK-DGPS giving centimetre accuracy is interfaced with gyro, tide gauge and the latest version of the Dippermaster backhoe control system from Seatec Underwater Systems BV of Zierikzee in the Netherlands.

Dippermaster provides on-line graphic and positioning data for the operator, with twin high brightness screens providing visual representation of the excavator in top view and side view. This information equips the operator to achieve incredible accuracy when dredging complex slopes and trenches.

The system also logs digmarks, allowing dredging data to be exported to disk in Excel format and/or sent to the Humber Work Boats office via GSM. Survey data can also be imported into Dippermaster via GSM. An incorporated safety feature is slew torque limitation, which prohibits the crane moving outside pre-set boundaries.

Pat M is equipped with a dedicated survey boat from which the intermediate survey data is transmitted directly to the Dippermaster computers for precise dredging and 'high spot' tracking. The vessel has an office/meeting room equipped with plenty of computer power points just below the wheelhouse, in which survey post-processing is undertaken and A1 colour bathymetric charts plotted for client examination.

Pat M has been built primarily for capital and maintenance dredging works in ports and harbours but a vast open deck lends itself to a variety of other potential applications. Some 400 tonnes of stability allows for a 100 tonne construction crane coming on board with space remaining to carry a rock armour deckload for placement in coastal protection works. Also within the Pat M's considerable range of capabilities will be trenching, pipe laying and removal, jetty demolition, mattress and outfall scour protection, and numerous other marine construction duties.

MJInformation 16726