Study on load characteristics of a podded propulsor in ice conditions and ice–propeller interaction modes based on full-scale ship measurements

Objectives The interaction between ice and propellers leads to significant differences in the load characteristics of podded propulsors operating in ice-covered waters compared with open-water conditions. Full-scale measurement data of ice-induced loads provide a critical basis for the safe and reliable design of podded propulsors operating in ice environments. This study aims to obtain full-scale measured load data of podded propulsors in ice conditions and to investigate the correlation between abrupt load variations and ice-propeller contact events, as well as the associated interaction modes during navigation in ice-covered waters.

Methods Based on theoretical analysis, a classification hypothesis was proposed for ice-propeller interaction modes, including ice milling, ice crushing, impact and ice clogging. Subsequently, operational data of a podded propulsor were collected during the Arctic scientific expedition of a Chinese PC3-class icebreaker, and the correlations among ship motion, icebreaking operational modes, and pod load fluctuations were systematically analyzed. A physics-informed method for the automatic identification and classification of ice-propeller contact events was then developed. The fluctuation characteristics of pod load parameters within event windows of different categories were compared, and their time-frequency features were further analyzed using wavelet transform.

Results The proposed hypothesis was verified, showing that ice-propeller interaction modes can be categorized into four types, namely milling, crushing, impact, and clogging. Under impact-type icebreaking conditions, the amplitude of transient peak fluctuations in pod torque reaches up to 160%, imposing the most stringent requirements on motor output control and over-torque capacity. The demand for propulsion capacity is most pronounced under low-speed, high-load icebreaking conditions in layered ice zones. In addition, ice thickness, ship speed, and test location exhibit strong coupling effects with the pod load levels.

Conclusions The correlation between pod load fluctuation characteristics, ice conditions, and ice-propeller interaction modes has been established. The full-scale measured data obtained in this study provide a quantitative basis for the load design of podded propulsors in ice-covered waters, and also offer essential support for assessing motor over-torque capacity and developing early-warning strategies for navigation safety.