A further step in the evolution of multipurpose, shallow draft work-vessels
During the last twenty years or so, the ?Multi-purpose work vessel? has enjoyed an evolution that now sees it positioned as an essential item of floating plant in several sectors of the marine industry, from fish farming to port construction.
Specialist Dutch shipbuilders Damen have been at the very heart of work-vessel development and the term ?Multi-Cat? has become almost a generic term for any form of self-propelled pontoon style vessel. It is fitting therefore that one of the latest and most powerful craft of this type was delivered recently by the Damen Hardinxveldt yard.
Designated a Damen Multi Cat 2611 the vessel, named Zwerver II, was constructed to a standard design intended for serial production but extensively customised to meets the needs of its Dutch owner HVS Dredging Support BV, of Harlingen. A long association with the dredging and marine construction caused HVS to look very closely at the type of vessel most suited to the services demanded by their clients. Zwerver II replaced an earlier and very successful vessel of the same name but of a very different type. The company chose to move away from the shallow draft tug configuration of the previous vessel to one combining a shallow draft with massive buoyancy for lifting and transportation, good sea-keeping qualities, yet retaining a significant towing capability.
Damen Shipyards of Hardinxveldt produced the design and the fabrication of hull and all major steelwork was carried out in Poland. Once completed the hull was towed to Holland to be fitted out in the company?s large building hall at Gorinchem.
In order to meet the owners requirements for draft and towing performance it was decided to opt for a triple screw propulsion system in a pontoon style hull of 26m length overall. The hull is rectangular in planform, with heavily radiused and fendered corners and a beam of 11.5m. The bottom plating is reinforced to permit deliberate grounding without damage, and the bow is rounded to improve waterflow and enhance seakeeping characteristics whilst underway. A rise in the deck of 40cm from aft to forward has also been incorporated to improve performance at sea and afford additional buoyancy. Three shallow tunnels formed at the stern accommodate the triple screw propulsion nozzles, shafts and rudders. The result is a vessel with a minimum draft of 1.75m, increasing to a maximum of 2.20m at full ballast/deck load condition. Other hull features include two 600mm diameter ?Spud? holes, one forward and one aft, and a 1.00m diameter ?Moonpool?.
To facilitate pushing operations, with barges and other floating plant, four heavily built ?push knees? have been incorporated in the bow to meet the owner?s specification. A 6m wide bow roller, for anchor-handling and lifting, has a diameter of 1.2m, and a safe working load of 150 tonnes. Bulwarks have been kept to a minimum and guard rails are used around the stern to prevent fouling during towing operation. Deck space has been kept as free from obstructions as possible, with the working areas protected by hardwood sheathing.
The design and position of the superstructure aboard and multi-purpose work-vessel is a compromise determined by the need to maximise the working area and locate the winches near or on the centreline. On Zwerver II the superstructure has been located hard over to the port side and carefully configured to encroach as little as possible on the working deck. A well-glazed wheelhouse has a slight overhang to starboard offering a good view of the work deck and winches. Two single drum Ridderinkhof winches are both installed on the vessel?s centreline and both can be operated remotely from the wheelhouse. The towing winch has a line pull of 30 tonnes and has been positioned as close as practicable to amidships. Situated adjacent to the towing winch is a Mampaey quick release tow hook of 30 tonnes SWL. A 500m steel wire towline of 36mm diameter is provided. A larger winch, designed for anchor-handling has a line
pull of 80 tonnes and carries a 100m of 50mm diameter steel
wire rope.
The choice of suitable cranes has become an important decision when compiling the specification for a new work vessel. When supporting dredging and marine civil engineering projects the ability to provide on-site lifting capacity for construction work and maintenance can prove a major advantage. In the case of Zwerver II, an Effer 160000/3SL capable of lifting up to 13.5 tonnes at a radius of 11.5m is mounted on the port bow. A second crane, an Effer 80000/SL is fitted on a mounting adjoining the towing winch fairlead. The latter is equipped with a winch and hoist wire and has a maximum lifting capacity of 6.2 tonnes at 11.6m radius. Both cranes are hydraulically operated with independent power packs.
Zwerver II is fitted with three Cummins KTA-19M3 main engines delivering a total of 1690kw. Power is transmitted via Reintjes WAF 364L gearboxes, with a 4.92:1 reduction, to fixed
pitch Promarin propellers of 1
.55m diameter. Each propeller rotates within a fixed ?Hodi-S?
nozzle supplied by Van Voorden Gieterijn. The steering system utilises three rudders and handling is improved considerably by the installation of a fully steerable, gill type, bowthruster. The latter is hydraulically driven and rated at 240kW.
On trials Zwerver II achieved a bollard pull of 28.2 tonnes ahead and 19.3 tonnes when pulling astern, and a maximum speed of 10.7 knots. Since the vessel has been in service its performance has far exceeded the owners expectations. Manoeuvrability is reported to be excellent and the ability to utilise the thrust of three propellers independently for precision positioning, when working with floating plant, has proved a substantial unforeseen bonus.
Two Cummins 6 BT5.9G2 generator sets of 98 kVA provide electrical power. Both deliver 220/380v at 50 cycles and one set is fully silenced. An additional Cummins N14 M 400 kW auxiliary diesel powers the deck hydraulic system. The rapid transfer of fuel and fresh water to other vessels can be carried out at 75 m3 per hour, through separate hose reels on deck. Integral tanks can accommodate 140 m3 of fuel oil, 60 m3 of fresh water and 90 m3 of ballast.
Fully air-conditioned, accommodation is provided for up to five persons in three cabins located below deck in the forward part of the vessel. The usual domestic facilities include a mess room, galley and washroom spaces.
The wheelhouse affords excellent all round vision and is well laid out for both navigation underway and working on site. A comprehensive bridge electronics package includes two Furuno radars, an FR 1505 ARPA set and an FR 1505 Mk III. Also from Furuno is a SC-120 Satellite compass, a GPS 80 and GR 800 D-receiver, and a FE-700 echosounder. The magnetic compass is an Observator Mk IV and the autopilot is a Sea Pilot 75. A chartplotter and display is configured with Tsunamis 99 Offshore software whilst radio communication is provided via two Sailor RT 4822 units.
Zwerver II is currently working on the ?Le Havre DPAM Port 2000? port expansion scheme, under contract to marine construction company Stemat for at least one year. The project includes working with large ?split hopper? barges in the construction of a new outer breakwater and support for dredging operations.
