New ship design requires better forecasting methods

Hydrodynamic improvement is one of the pillars to enable more energy efficient shipping. This requires that the methods and tools for hydrodynamic performance evaluation continuously follows the development of technology and meets the accuracy requirements.

Foto: Shutterstock.com

Foto: Shutterstock.com

In a Lighthouse pre-study, written by Sofie Werner, SSPA, a proposal are submitted for a research and development agenda regarding the methods used to forecast vessel performance in calm water. The long-term goal is not to let the standards and methods used in the hydrodynamic design of ships stand in the way of energy-saving innovative design, as is the case today.

Correct forecast important
The following example shows what major effect on energy efficiency a possible incorrect forecast can have:

During the design of a new vessel, two innovative propellers from different manufacturers should be selected. Comparative model trials are performed. One propeller is 3% more efficient, ie the ship will use 3% less fuel. Due to errors in the evaluation method, this isn’t known. If you then choose the "wrong" propeller on the basis of incorrect results, you can lose a fuel saving of 3%. If the ship is built in 10 copies and has a running time of 25 years, it will be a lost fuel saving of 170,000 tonnes, which corresponds to approximately 2000GWh (80MWh / year).

New opportunities
Achieving energy efficiency of vessels requires proper standard methods for performance evaluation in the design phase. Today's methods of extrapolating model test results have worked well for many years. Now, the required accuracy has been raised and with new innovative design, the scope has been expanded. The emergence of calculation methods, CFD, has provided new opportunities to improve methods.

It is also found that CFD-based predictions cannot completely replace model tests for this purpose. Instead, we propose the development of hybrid methods, which use both experiments (EFD) and calculations (CFD).

In order for the new methods to be reliable, a major development work is required concerning the confidence of CFD calculations. A research agenda is proposed and the process of applying for research funding has already begun.

The pre-study has been funded by Lighthouse. Financing has also been obtained from Hugo Hammar's Fund for Maritime Research. The work was performed by Sofia Werner, SSPA Sweden AB and Rickard Bensow, Avd. Marin Teknik, Chalmers University of Technology.