Despite frequently being seen as the cheap workboxes of the global dirty ore and coal trade, bulk carriers must comply with a growing number of efficiency, safety and environmental regulations.
DNV GL recently assisted with bulk carrier optimisation services for hull and machinery for a new type design Ultramax-size vessel called Diamond 2.
Type Designs Bear High-Level Engineering Efforts
Ships with the fullness of a bulk carrier are difficult to analyse with CFD due to a high share of viscous effects in resistance and propulsion. This makes hydrodynamic optimisation of bulk carriers expensive although the outcome is considered marginal compared with a faster container vessel with even more installed power. The building costs of a bulker often hardly exceed steel price. Properties that could cancel any thought for high-level engineering such as optimisation immediately, if there was not the fact that there is such a large fleet of bulkers sailing the oceans. A good reason for Graig Shipping Group and Econovo to get into the market with a state-of-the-art Ultramax type design from which presumably around 100 units will be delivered.
World-Leading Technology for Hydrodynamics
For the hydrodynamic hull design, the well-known ECO-Lines services of DNV GL were used. The Diamond 2 received the complete package of treatments from wave reduction and aft-body propulsion optimisation on to an optimised twisted aft ship and a highly efficient design propeller. As usual, CAESES is linked in the process chain for automatically generating the hull geometry. From there, all necessary data such as constraint values and numerous outputs for robust analysis, such as reparametrized surfaces for grid generation in FS-Flow and STL meshes for the OpenFOAM-based RANS solver. This setup is a very powerful and efficient design process, to quickly find the optimal design candidate.
Promising Performance Prediction
For this bulk carrier optimization, the objective is the power consumption on five draft/speed combinations with typical time-at-sea weightings (operational profile). Whereas ships with high wave resistance ratio often see double-digit optimisation results, it is a huge success for a bulker to be improved by 5% in the operation range. The ship was tested in SVA Potsdam (before the application of an asymmetric stern, see below) and was compared to an anonymous fleet of 4 similar vessels. The graph for the design draft condition is shown below:
The final hull features an optimised asymmetric stern instead of appendages. Simulations show another 2.6% power reduction due to the twisted inflow. A high-efficiency propeller and a rudder with a vortex-reducing bulb complete the propulsion system. Graig expects the efficiency enhancements to result in fuel consumption of 14.6 tonnes per day at an optimised speed of twelve knots.