In March 2016, two full-scale ice trials were performed between Oulu and Kemi in the Bay of Bothnia – the northernmost part of the Baltic Sea – where ice conditions are extremely hard during cold winters. The first trial was to perform ice trials for the Finnish Border Guard’s offshore patrol vessel Turva. The second was to test the newly developed bronze propeller in heavy ice.
The bronze propeller for ice has been developed by Aker Arctic Technology in co-operation with Finland’s TEVO and VTT Technical Research Centre of Finland. Although not as strong a material as stainless steel, bronze has some advantages over a stainless steel propeller. It offers better corrosion resistance, it is easier to manufacture and maintain, and it is cheaper. Bronze is a widely used marine propeller material in open water and TEVO wanted to find out if it would be feasible to use it in ice-going vessels, too.
The bronze propeller was fitted on the Finnish Navy’s multipurpose vessel Louhi. The vessel was designed as an oil and chemical spill response vessel and is owned by the Finnish Environment Institute (SYKE), but is manned by the Finnish Navy.
Louhi is equipped with two azimuthing thrusters with stainless steel propellers, but for the trial one propeller was replaced with a bronze propeller. The tests were performed in both ahead and astern direction in 60cm and 85cm thick level ice, 6m thick ice ridges, and ice channels.
“The conditions for extreme ice conditions were excellent,” said Kari Laukia, Aker Arctic head of ship design and engineering. “We wanted to test the propellers in conditions that were as heavy as possible. We succeeded in finding different conditions that were suitable.
“In addition to strength measurements, we took underwater videos in order to see how the ice and propeller interaction took place. After the testing, Louhi returned to drydock and the test propeller was remounted and sent to TEVO for inspection.”
The conclusions based on the test results are that the bronze propeller can be suitable for vessels in 1A Super ice conditions. The testing conditions gave reliable results and input for the propeller design for 1A and 1A Super ice class vessels.
Louhi was built by Uki Workboat in 2011. It is a multipurpose response vessel designed to operate in all Baltic Sea ice conditions and fitted with an extensive mechanical oil spill response outfit, including equipment designed specifically for collecting spilled oil in ice conditions.