Energy efficiency and environmental considerations are key driving forces determining maritime operation. Economical pressure and international legislation require energy resources to be used sensitively and the associated emissions to be reduced as well as properly treated.
The TARGETS project aimed to support the development and operation of energy efficient ships. Specifically, it sought to provide substantial improvements to cargo ships’ energy consumption.
The prime goal of TARGETS (Targeted Advanced Research for Global Efficiency of Transportation Shipping) was to undertake a global analysis of the most important causes of energy consumption on board of cargo ships in a comprehensive and holistic approach. Having identified resistance and propulsion aspects as primary causes of energy consumption, work will be dedicated to the improvement of such characteristics.
TARGETS assembled a team of leading European fluid dynamics and energy specialists as well as major EU shipping operators, covering container, bulk and tanker cargo operations. The project set out to develop designs, tools and operational guidelines for the energy efficient operation of cargo ships.
The TARGETS project combined the principal elements determining the use of energy consumption on board a cargo ship and integrated them in a holistic simulation to determine optimal solutions. The project’s findings indicate that:
- For form related resistance, computational speed is an important factor determining the efficiency of –RANS based – optimisation processes. Significant speed ups could be achieved for volume of fluid based free surface computations through pre-conditioning and algorithmic improvements.
- The second largest resistance component is due to viscous forces which depend on two main parameters: the viscosity of the fluid and the surface quality. To assess the potential of modern coatings, extensive tank tests have been run to measure the losses associated with surface deterioration and fouling. Depending on the surface condition, significant increases up to 50% have been found for (heavy) calcareous fouling. These findings have been implemented in a scaling procedure which allows to determine the effect of surface deterioration at full scale during operation.
- The effect and net gain of the air lubrication varies strongly. While full ships such as bulkers or tankers show significant benefits, the net gain obtained on slender hull forms is negligible.
- The BLAD – Boundary Layer Alignment Device is meant to work further upstream of the propeller and deflect outer streamlines into the propeller plane, thus reducing the typical axial flow deficiency in the 12 o’clock position of the propeller and harmonising the inflow condition. Using an asymmetric arrangement on port- and starboard side further creates a swirl against the propeller rotation to generate extra thrust. Together with an adapted propeller this yields a reduction of more than 7.5% of PD at the design point.
- The implementation of Speed Selection Optimisation seems to be more promising in comparison to Trim and Ballast Optimisation.
- Wherever reduced speed is not an option, e.g. in a regular scheduled service, CFD simulations which have been performed for the car carrier and the container ship, indicate that some gains can be obtained through trim optimisation as well. The results of the study indicated that there is no common trend between the different vessels investigated Each ship needs to be treated individually, based on the specific hull form, before deciding which trim option is best.
Similar to ship hulls, propeller performance will be affected by surface quality. Deterioration in form of roughness or fouling will increase losses in propeller efficiency due to increased friction. Hence propeller cleaning is an appropriate means to improve the performance of a ship in service. A new prediction algorithm based on Schulz’s method was developed in TARGETS to quantify these losses and hence allow to assess the evolution of propeller performance over time during operation. The method includes an established relationship between the drag and roughness of selected commercial coatings (soft and hard) using experimentally established data from representative coated flat surfaces. The algorithm has been built in an in-house propeller analysis code.
Some energy saving potentials will have better results in container vessels while others are more suited to fuller vessels like bulk carriers and tankers. TARGETS has investigated a large number of energy saving potentials and categorised the different identified ESPs with respect to their suitability for various applications and effect.
- Resistance improvement technologies
- Propulsion Improvement Technologies
- Improved auxiliary on-board energy generation
Although the establishment of Energy Efficiency Design Index [EEDI] is an encouraging step towards the extension of existing environmental regulations and it addresses the issue from the design stage, further development is needed considering that:
- It represents the ship transportation CO2 efficiency at a single point during the life span of the ship disregarding at a stroke operational and maintenance practices;
- The specific fuel consumption of auxiliary engines has minimal impact on EEDI, a rather misleading fact since the installed electric power capacity depends on mission requirements and safety margins;
- Larger payload capacity leads to improved EEDI (the capacity term is in the denominator) and renders larger ships more environmentally friendly in comparison to smaller ones.