The stationkeeping performance prediction of a Dynamic Positioning (DP) vessel greatly depends on the accurate modelling of the ice forces, which in turn depends on managed ice field characteristics (ice concentration, floe thickness, floe size, ice drift speed and direction and inclusion of brash ice and small ice pieces) and the DP system characteristics (DP gain set-ups, control algorithms etc.). Physical model testing is a key tool in understanding and validating the fundamental relationships between the ice environmental parameters and the dynamics of a DP vessel. The National Research Council's Ocean Coastal and River Engineering Research Centre (NRC-OCRE) has conducted two comprehensive series of experiments with one 1/40 scaled and one 1/19 scaled DP vessels, in various realistic managed ice conditions in the ice tank facility in early 2015 and in early 2018, respectively. The primary objective of the model testing programs was to generate a database on managed ice-DP vessel interactions, which was the core to NRC-OCRE's ice force model development and validation activities. This paper describes the model test planning, preparation of managed ice field, the procedure of the model tests and the methodologies of data analysis for the two model testing programs. In both programs, the physical and mechanical characteristics of the ice field were modelled by controlling ice concentration, ice thickness, floe size, ice strength and the ice drift speed and direction. The ice concentration ranged from a light condition (7/10th) to a very heavy condition (9/10th+) with multiple ice floe sizes ranging between 12.5m to 100m. Multiple ice thicknesses ranging between 0.4m to 2m were used for multiple ice drift speeds (0.2 knots, 0.5 knots, and 1.2 knots) with various moderate to extreme ice encroachment angles. Ice forces were not measured directly but estimated based on the thrusters’ response. In addition, model's 6-DOF motions and accelerations were recorded. Multiple high definition cameras were used to capture the global and local ice-structure interactions both placed in above water and underwater locations. For the 2018 testing program, a new ceiling based video system was introduced that captured the images of the ice basin at multiple overlapping locations, which were processed offline to obtain time sequence full image of the ice basin. Model testing results for a few representative cases are presented in this article. The DP system used in the testing demonstrated capabilities of the vessel in maintaining station for majority of test cases. The measurements as well as the videos showed complex and highly stochastic ice-ship-boundary wall interactions, particularly for high oblique cases. The data and video captured provided sufficient information for developing novel ice force models for real time applications.

No abstract

Polar navigation entails challenges that affect the continuation of ship operations in severe ice conditions. Due to ice-propeller interaction, propulsion shafting segments are often at a high risk of failure. Efficient methods for shaft line design are hence needed to ensure the safety of ice-going vessels and propulsion reliability. To this end, full-scale measurements have proven essential to support the development of ship-design tools and updated safety regulations for ice-going vessels. This paper presents a unique integrated measurement system that employs measuring equipment to monitor Polar-Class vessel performance and shaft line dynamics during ice navigation. The system was installed on board the Canadian Coast Guard (CCG) icebreaker Henry Larsen. This experimental concept aims to monitor the shaft’s torque and thrust fluctuations during ice navigation to obtain information about the ship’s propulsion efficiency. In the paper, we describe the arrangement of the measurement system and the components it features. Finally, we present preliminary datasets acquired during two icebreaking expeditions. This work is framed into a broader research project, which includes the long-term objective to determine a correlation between sea ice conditions and the dynamic response of shaft lines.

This paper describes the results of model tests carried out in ice and open water conditions to evaluate performance of the United States Coast Guard (USCG) Heavy Polar Icebreaker (HPIB) indicative design. The resistance, propulsion and manoeuvring performance in ice conditions was evaluated at three different ice thicknesses (4, 6 and 8 ft.) with flexural strength 100 psi using two power setups, 36500 HP and 65000 HP. Calm water resistance and propulsion tests were also performed to evaluate open water performance. Models were constructed and tested corresponding to two indicative designs, one with triple shaft propulsion system and the other with one centre shaft and two wing podded propulsors. The present paper describes only the results for the model with triple shaft propulsion system.

This paper provides the results of model tests in ice to evaluate the performance of the USCG Mackinaw Icebreaker that was equipped with two podded propulsors and compares with the data obtained from the full-scale ice trials. The objective of this collaborative model test program between the NRC and USCG was to understand the capability and limitation of the model tests with podded vessels in ice. As a result, the model tests showed a good agreement with attainable speeds at selected power levels but an overestimation of the ice resistance by an average of 7% (from 10% to 25%). Further discussion of podded icebreaker performance including turning circle tests in ice is provided and future work is proposed. This paper also provides a discussion of two different flexural strength test methods, which are simple beam and cantilever beam tests. Introduction The number of icebreakers with podded propulsors has been increasing in recent years and many new icebreakers are planning to use the pods because of high maneuverability and additional benefits such as low noise and vibration, and various usages of the propeller wake. The first pod unit (1.3 MW) was installed in a utility vessel Seili in 1990. Since then, several ice-going tankers/ icebreakers have used single or multiple pod units, which had up to 16 MW power (Wilkman et al. 2018).