The Less You Burn, The More You Earn

Within the maritime shipping industry recently are, among other things, the effects of shipping on the environment, emissions reduction, political regulations in shipping areas, and a lifetime improvement of vessels and cutting back fuel prices.There are eleven companies and institutes from six European countries that have collaborated in a three-year project that took a closer look at a solution for these matters.

Green Retrofitting through Improved Propulsion also known as GRIP is a European Collaborative Research Project, which aims at improving insight in the working principles of Energy Saving Devices (ESDs), also in fuel reduction and providing a sound basis for the choice of a specific ESD. The research project also aims to show that fuel consumption in shipping can be reduced by more than five percent. GRIP is dedicated to contributing solutions to important matters like reducing exhaust gas emissions and cut back fuel costs.

A lot of concepts

An ESD is designed to prevent energy losses in the ship propulsion system, or to redeem a part of these losses. Professor Tom Van Terwisga, senior project manager at MARIN, explains: “You can never redeem more energy than you have lost, which is a hydrodynamical and scientific starting point. ESDs can be installed in front of the propeller, to prevent energy losses, or behind the propeller to win back the loss. There are a lot of different ESD concepts and the question remains how they work and which energy losses they prevent.”

Anton Voermans, supervisor hydrodynamic engineering at Wärtsilä, explains that the development and application of ESDs goesway back to the 1970s: “Most ESD designs were not that successful because their effects were often determined from experiments in model basins. When implementing the ESD on full scale it would mostly not function as thought or not function at all, because of scale effects. Nowadays those scale effects can be taken into account with the modern calculation techniques like CFD (Computational Fluid Dynamics, ed.).”

Applause for the EU

The GRIP-project does not stand alone, but can be seen as part of a strategic research and development policy says Van Terwisga:

“When I look back on the long-term strategy of the European Union in the area of retrofit, I can only say that they have handled the subject very well. The first EU-financed projects regarding ESDs started in the 1990s. The Calypso-project, for example, researched hull optimization. In 2005 the Virtue-project took off, aimed at improving and integrating state-of-the-art CFD tools in a comprehensive simulation environment of ship behavior. Then the Streamline-project was started, which investigated several state-of-the-art propulsion systems and new propulsions systems combined with advanced CFD for accurate analysis and design of these propulsions. GRIP is the successor of the Streamline-project, in which we aim to optimize ESD designs with CFD. These four projects cover around 16 years in which the European Union supported the development of a retrofit tool that comes in handy with the current regulations.”

Voermans: “The GRIP-project started by making an inventory of all the types of ESDs, their working principles and which ESDs can be used for retrofit. We also had a look at the known certainties and uncertainties when calculating the effects of these ESDs, and how these computations could be done as accurate as possible. Then the structural aspects of ESDs were taken into account, since they need to be strong enough to stay attached to the vessel in heavy seas and we wanted to know what the most efficient way is to attach the ESD to the vessel. And in the final stage of the project, we put our findings to the test by retrofitting a bulk carrier with an ESD.”

Sharing knowledge

Under the vast leadership ability of Wärtsilä an Early Assessment Tool also known as EAT was developed. The extended version is only available for the consortium; however the simplified version is shared online with the world so interested parties, like ship owners, can make a first estimation of the costs and the payback time.

Voermans says: “To develop the EAT two basic questions needed to be answered: what do we expect from the EAT and which vessel types and ESDs are there. The owner of a vessel wants to gain certain information by using the EAT, like the possibility to install ESD Y on vessel X, the costs for the retrofit, the fuel savings, the profit and of course, the payback time. Furthermore, we took a closer look at all the different kind of ESD-types that are currently available. Based on a set of assessment criteria we defined the pre swirl stator, the pre duct and the propeller hub loss recovery devices as most successful and took these types further into account during the development of the EAT. Then, all the vessel types in the world fleet were closely examined. Based on the criteria of how many of each type were present in the world fleet and the amount of fuel they consume. We focused the EAT on tankers, bulk carriers, container vessels, short sea shipping cargo vessels and ferries.”

The structure of the EAT contains three sectors that ultimately lead to an economic business model from which the ship owner can tell if the selected ESD is a go or no go for his vessel type. The cost model is parametric aligned to amongst others the diameter of the propeller and the installation costs. Wärtsilä developed this model in collaboration with the shipyards in the consortium, Fincantieri and Uljanik Shipyard. There is the hydro model that makes an estimate of the efficiency improvement that can be achieved and the fuel cost model that calculates the fuel consumption for each vessel type per year, based on sailing days and engine fuel consumption.

Voermans: “To add to this, users of the EAT also have access to a literature database. All available literature on the subject of ESDs is screened and reviewed by the consortium partners. We found 110 papers in literature we deemed usable. Interested parties can look up the working of an ESD for example, or the effects measured before in research.”

Flow models

To calculate the flow dinamics in energy saving by using ESDs, Van Terwisga was asked to get involved:

“CFD is used to calculate the dynamics of the flows. In short, you place three-dimensional cells in the flow domain of a vessel, and for each of those cells a system of flow equations is then solved. A vessel with a propeller typically has around five to 40 million cells. The solution of the equations yields amongst others the local flow velocities, the shear stress on the hull of a vessel and the thrust of a propeller. This information provides a very detailed insight into the effects of the flows on both model and full scale, which cannot be gained by doing model tests in basins. With this information you can, for example, examine the type and distribution of your energy losses.”

Each of the three research and engineering companies involved, MARIN, VICUSdt and HSVA, contributed to the project by each designing an ESD on a specific bulk carrier named Valovine. The ESDs selected were a pre swirl stator, a pre-duct and a rudder bulb. Shipyard Uljanik in Croatia put one ESD to the test on Valovine. The results of the design exercises were checked by MARIN in a final calculation from which it eventually appeared that the pre swirl stator was the best option for the sea trials, requiring some 1.2 per cent less power than the second best ESD, a pre-duct.

Van Terwisga tells a little more about performing CFD:

“You start by defining the geometries of an ESD, think of the size of its wings and their angle. The pre-optimisation takes a closer look on the design and then the simplified flow models are used to perform the first optimisation calculations. When finding the optimum within the model, a CFD model is used to check the former results and come closer to the real optimum. Most of the time, this deviates from the results found in the early stages because CFD computation is typically is more accurate. Then, finally the computed power saving of an ESD on a specific vessel type is found. For the bulk carrier we calculated a power gain of 3.7 per cent.”

Better than expected

In Croatia where trials were conducted, the results were even better. A power gain of 6.7 percent was found, which was more than expected and a clear result of the project. Voermans: “I think the project has been very successful. The mix of partners was very good, everybody collaborated and the project has already delivered a spin off. We are very happy with the results.”

Van Terwisga adds: “The biggest success of the project is learning about and getting insight in the principles of energy saving devices. By knowing those principles, it is way easier to tell if a device is suited for a vessel or not. Furthermore, we learned how to use the CFD models for as accurate calculations as possible and how accurate the solutions actually are. Eventually I expect that these results will contribute to a few optimal configuration of ESDs and that we will see the large number of different types to be reduced to perhaps some three popular concepts. The knowledge we gained can be used in the day-to-day service.”