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Aframax tanker with asymmetric aftbody under construction at GSI

for the Swedish shipowner AB Gotland. Guangzhou Shipyard International Company Ltd. (GSI) and MARIN closely cooperated for this project. An extensive model test campaign was performed to optimise the propulsive performance of the vessel. The propeller and rudder cavitation and manoeuvring capabilities of the vessel were also evaluated and optimised. In early 2018 full-scale trials were performed on the first vessel that was delivered. The trials were in line with the model test predictions.

Minimum power requirements To reduce the emissions of the shipping industry, vessels need to comply with the Energy Efficiency Design Index (EEDI). This is beneficial for the environment, however in some cases the safe operation of the vessel might be at stake. One of the measures to reduce the EEDI is to lower the installed power on board the vessel. For some full block vessels, this can compromise the safe operation of the vessel when sailing in adverse weather.

Together with Shanghai Waigaoqiao Shipbuilding Co., Ltd. (SWS) a study was recently done on the minimal power requirements for a VLCC. In order to

determine the minimum power requirement according to MEPC.1/Circ.850/Rev.1, a Quadratic Transfer Function of the wave added thrust was determined by means of wave added thrust tests in regular waves. The minimum required power was determined and checked with the available power.

Asymmetric aftbody Together with Guangzhou Shipyard International Company Ltd. (GSI) MARIN recently developed an asymmetric hull for an Aframax tanker (Dang et al., 2015)2

. An asymmetric aftbody

is a type of Energy Saving Device (ESD) which can generate a pre-swirl in the propeller wake to improve the interaction with the propeller, but without adding additional appendages on the hull. To maximise the energy efficiency of the vessel, the hull form and propeller were designed simultaneously. By using a RANS-BEM coupling, thousands of hull form variations and propeller geometries were evaluated overnight, resulting in a fully-integrated, hull-propeller design (Ploeg & Foeth, 2013)3

Cavitation observations, hull pressure measurements and manoeuvring model tests were also carried out and showed normal behaviour compared to the symmetric tanker. Finally, feedback from full-scale measurements confirmed the findings of the model tests.

The overview shows that the Chinese market is interested in high-end development of knowledge and ship design supported by MARIN. We are looking forward to continue cooperation with Chinese shipyards and design offices in the future.

1 Hooijmans P.M., van der Meij K.H., Greening D., Yu L. (2014). Traditions Broken in Modern Container Ship Design. Design & Operation of Container Ships, London, UK.

2 Dang J., Chen H., Rueda L., Willemsen H. (2015). Integrated Design of Asymmetric Aftbody and Propeller for an Aframax Tanker to Maximize Energy Efficiency. Fourth International Symposium on Marine Propulsors, smp’15, Austin, Texas, USA.

. Calm water model

test results showed more than a 6% reduction in required shaft power compared to an optimised symmetric hull form.

3 van der Ploeg A., Foeth E-J., (2013). Optimization of a chemical tanker and propeller with CFD. Proceedings of ECCOMAS International Conference on Computational Methods in Marine Engineering V, Hamburg.

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