An unusual set of operational challenges has led to an innovative, front-loaded propulsion arrangement on a heavy cargo deck carrier under construction at Jiangsu Zhenjiang Shipyard.
Designed by Hamburg-based engineering company HeavyLift@Sea, the vessel will transport very heavy but fragile turbine components that must be rolled rather than lifted onto the deck. The carrier will operate in the North Sea and Baltic for offshore wind specialist UNited Wind Logistics.
HeavyLift@Sea managing director Hendrik Gröne explained that this operational requirement, demanding a wide cargo deck, had to be balanced against other constraints. "The deck width had to be reconciled with a ship that was small enough for the approach to a particularly small Danish port and to meet the requirements of the Kiel Canal," he said.
The ship design squeezes 3,600m2 of deck space, with a loading capacity of 10,000 tonnes at maximum draught, onto a vessel that is 148.5m long and just 28m wide. This was achieved in part by making the superstructures, including the 21-person accommodation block, as compact as possible.
The requirement for deck space also proved challenging for the propulsion installation, especially for the positioning of the exhaust funnel and selective catalytic reduction units. Project manager Frank Schernikau explained that deck space was optimised by putting the funnels near the superstructure close to the bow of the vessel. But putting main engines at the fore would usually require a very long propeller shaft, disrupting the layout across the length of the ship and increasing the risk of alignment issues.
The solution was to opt for a diesel-electric configuration, with engines installed near the ship’s bow and a propulsion room with electric motors driving fixed-pitch propellers via conventional shafting in the aft. Although the diesel-electric configuration is not as efficient as directly driven propulsion due to conversion losses, it regains some of the lost efficiency by allowing engines to be run at a consistent, optimal load, which also reduces engine wear.
The shipyard has ordered two MAN 9L 21/31 and two MAN 6L16/24 gensets for the DP2 vessel. Steel was cut in November and delivery is expected at the end of 2019. Meanwhile HeavyLift@Sea has been awarded the basic design contract for the shipowner’s next vessel, a special ship for offshore wind operations.