Article / 15.07.2024

R&D: Energy saving devices evaluated in ice operations

Different types of energy saving devices (ESD) can be used to improve the propulsive efficiency of a ship. With benefits such as lower fuel consumption, reduced emissions and vibrations, their popularity is growing. Therefore, the suitability in ice operations was investigated at Aker Arctic.

Due to tightening emission requirements and economic benefits, the installation of energy saving devices (ESD) is increasing, both in new ice-classed ships and as retrofits in existing vessels. According to manufacturers, the propulsion power can be reduced up to 8% using a pre-propeller ESD.

Aker Arctic’s research team conducted a series of model tests in late 2023 to find out how the devices function in ice operations, if there are any risks involved in using them, and to solve potential problems. The objective of the tests was to investigate how clogging of pre-propeller wake-equalizing ducts with ice influences propeller and vessel performance.

Position of the pre-propeller ESDs in relation to the propeller.

Two different pre-propeller ESD types were investigated: a Becker Mewis-type duct with fins installed in front of the propeller and a Schneekluth-type wake-equalizing duct located further from the propeller. Both devices were evaluated with a gradually increasing level of clogging with the vessel stationary and moving forward at a constant speed of 5 knots.

Propulsion performance drops with speed

The results from the research indicate that the performance of the vessel will drop if the pre-propeller ESD becomes clogged with ice. The effects were more significant with an ESD solution located closer to the propeller. Additionally, devices equipped with both fins and a duct can potentially clog easier than devices consisting only of a duct.

The negative impact was greater with the vessel moving forward compared to a stationary vessel in a bollard pull situation. As a result, a cargo vessel may stop due to an inability to maintain sufficient speed in ice conditions, if the ESD becomes clogged.

Influence of the clogging to the net thrust of the vessel. The net thrust values of the clogged ESDs are compared to the open ESDs at constant power level and at same speed.

In addition to the propeller performance, vibrations due to clogging were also investigated. The results indicated that the vibrations due to clogging are greater with an ESD located closer to the propeller, compared to the type installed further away.

It was also discovered that a partially clogged ESD caused more thrust deviation than a completely clogged ESD. Therefore, the vibrations due to partial clogging may stop a vessel anyway, regardless of propeller performance.

Influence of the clogging to the thrust deviation at bollard pull.

Shallow draught increases risk

Development Engineer Teemu Heinonen, who was responsible for the project, highlights that clogging is generally an unlikely event, but a small vessel could potentially have its ESD clogged by ice when sailing in ballast in difficult Baltic Sea ice conditions.

“Probably the most efficient method to avoid clogging is to have the stern loaded deep enough. It is important to pay attention to the minimum draught in which the ice-classed vessel equipped with a pre-propeller ESD is allowed to operate in ice,” he says.

Heinonen adds that minimising such risks is something Aker Arctic can assist with during the design work.

Influence of clogging to the propeller efficiency calculated based on the net thrust for the model equipped with a Becker Mewis -type ESD. The efficiency represents relative efficiency when compared to the ESD without clogging.

Influence of clogging to the propeller efficiency calculated based on the net thrust for the model equipped with Schneekluth -type ESD. The efficiency represents relative efficiency when compared to the ESD without clogging.

Research supports authorities

Aker Arctic supports Finnish and Swedish authorities by conducting research on various topics related to commercial shipping in ice. The Winter Navigation Research Board, a cooperation between Finnish and Swedish authorities, selects and funds research topics yearly for many organisations.

“The Winter Navigation Research Board was founded in 1972, and Aker Arctic and our preceding companies have cooperated with them since the beginning,” Heinonen notes.

Overall, Aker Arctic’s research work includes basic research, confidential research projects for customers, internal development projects, and cooperation projects with universities and research institutes. In addition, the company offers multiple master’s thesis research projects to university students every year.

“Research and development are extremely important for us, as it ensures we stay ahead in our field of expertise and continually implement new ideas to improve operations in ice,” Heinonen says.

He adds that from a sustainability perspective, energy efficiency in ice-going vessels is a top priority in Aker Arctic’s design work.

“Higher energy efficiency results in lower fuel consumption which reduces emissions. At the same time, operational costs decrease. This is a win-win situation from all viewpoints,” Heinonen underlines.

Text: Catarina Stewen