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Entering a new environment, meeting new people or trying a new activity can be intimidating. For some reason, taking a deep breath always seems to help take the edge off. That's right, taking in some air can help you break the ice in a more natural and confident manner. But did you know the same idea applies when literally breaking the ice?
Seafaring on ice-covered water
Marine shipping is an essential service for delivering goods to many Canadians. But navigation in Canadian waters can be challenging—the presence of ice in the water requires proper route planning and safety measures.
To address this challenge, the Canadian Coast Guard fleet is equipped with icebreakers to break the ice and clear the path for other vessels. Icebreakers also have the capacity to rescue ships that sometimes end up stuck in ice or struggle in harsh conditions, unable to retreat or continue along their route. These icebreakers are crucial to maintaining active and safe operations, such as helping deliver goods to coastal and Arctic Canadian communities. However, when icebreakers are travelling in heavy ice conditions, hull-ice friction can cause much higher resistance, more challenging manoeuvres and lead to increased fuel consumption and emissions.
To improve the safety and performance of ice operations and to reduce the carbon footprint of the Canadian fleet, the Canadian Coast Guard sought the expertise of the National Research Council of Canada (NRC). Together, they're assessing the powering performance of current from the Coast Guard's icebreaker Henry Larsen with an air bubbler system.
The air bubbler system forces low-pressure air through nozzles located in the ship's hull, below the waterline. The main advantage provided by this system is a reduction in the hull–ice friction by lubricating the hull surface with water agitated by air bubbles. The system can function like a bow thruster in tight areas to gently remove the ice near the wharf or be used to widen the channel behind the icebreaker when escorting other ships. Using the air bubbler system can also reduce the onboard noise and vibration caused by the interaction of the hull with the ice.
"We had anecdotal evidence that the bubbler system was beneficial on existing icebreakers. However, there were no data to conduct detailed engineering work and identify the system design performance for the new classes of vessels. Given our successful relationship with the NRC in the past, it was natural to work with their Ocean, Coastal and River Engineering Research Centre to develop a plan to gather the information we required," says Catherine Le Blanc, former project manager of the Future Capability Development project for Vessel Procurement, Shipbuilding and Material at the Canadian Coast Guard.
Assessing new technology
Prior to implementing the air bubbler system on the Coast Guard's new icebreaker fleet, experts from the NRC's Ocean, Coastal and River Engineering Research Centre built a scaled model of the Coast Guard's Henry Larsen without the air bubbler system. Once the model was functional, it was tested in both the NRC's 200-metre clear water tank and the 90-metre ice tank facility, located in St. John's, Newfoundland and Labrador. This research facility is fully equipped to recreate and simulate realistic open water conditions and Arctic or harsh conditions, often experienced in Canada. The ice tank can reach temperatures as low as -25°C and has the capacity to produce ice sheets up to 76 metres long, 12 metres wide and 200 millimetres thick. This allows a ship's powering performance to be evaluated in both open water and ice. The data collected from these tests were used as a baseline to compare performance with that of the model equipped with an air bubbler system.
NRC experts then conducted field trials on the Coast Guard's Henry Larsen, which operates in the Gulf of St. Lawrence in the winter months and in Canada's High Arctic in the summer and fall. The vessel was equipped with the air bubbler system and state-of-the-art instrumentation, including optical thrust and torque measurement units (optical sensor, TT sense®), and ship operational data, visual data as well as environmental data.
The 13-day field trials took place in March 2022 off the coast of Newfoundland and Labrador. Results showed that the air bubbler system allows for higher speeds due to reduced hull–ice friction, faster accelerations, advanced ramming capability and improved powering performance in some ice conditions. Results also showed that the system can be used like a bow thruster or to widen a navigable channel behind the icebreaker when escorting other ships.
To support this study as well as future studies on marine autonomy, the NRC contracted C-CORE, a Canadian company that specializes in ice engineering, geotechnical engineering and remote sensing, to deploy situational awareness sensors, including LiDAR systems, stereo cameras, panoramic cameras and electromagnetic and acoustic sensors.
"Whenever we get the opportunity to hop on a ship with the Canadian Coast Guard and perform field trials, it's really motivating for our research teams. We love collaborating with the Coast Guard to improve the safety and the efficiency of their marine operations in our harsh Canadian conditions. We're very proud to be part of this effort and to contribute to the next generation of Coast Guard ships in Canada," says Fraser Winsor, Ocean Program Theme Lead for the NRC's Ocean, Coastal and River Engineering Research Centre.
Keep cool and carry on
This study has shown that the air bubbler system is a valuable tool for the icebreaker operator. Future model tests by the NRC will help determine if the orientation of the air bubbler can be optimized to further enhance ship performance. The NRC is also considering expanding these studies using electrically powered alternatives and to assess the ability to control the air bubbler system power with a range of settings from low to high, which would allow for more precise operations, and to evaluate real-time energy consumption of the air bubbler in relation to the ship's performance to optimize the usage of the air bubbler system.
The next step is for the NRC to test the ice model in the facility with a scaled model equipped with an air bubbler system to better understand issues that were identified with the full-scale model and provide solutions. When complete, this study will allow the NRC to offer guidance on optimum air bubbler locations and air bubbler powering, contributing to increased icebreaker efficiency and reduced carbon footprint, without sacrificing performance.