Making sense of speed effects on ice crushing pressure-area relationships in IACS ice-strengthening rules for ships

Abstract

Arctic shipping fleet expansion is anticipated in the future. However, future refinements in the understanding of ice loads on larger ships are needed to achieve a better structural design with reduced steel weight. Published rules for the strength of ships are derived from semi-empirical methods and calibrated with limited full-scale measurements on small ships. In 2015, the Lloyd's Register pointed out that for independent navigation of larger ships in heavier ice conditions, steel weight increases exponentially with the ice thickness, which negatively affects the economy of ships' operations.

Motivated by this statement, the objective of this paper is to address uncertainty in rule-derived ice loads using an ice mechanics point of view. The focus is on the local ice crushing loads and the vessel speeds in the Unified Requirements for Polar Class Ships of the International Association of Classification Societies (IACS).

In this work, we attempt to relate the IACS speed-dependent ice pressure-area relationships to the simplified principles of ice mechanics coupled with structural design considerations. This relation enables us to better understand uncertainties in the rule loads for larger ships, which is essential to address the economy of Arctic ships’ operations. The results of this study showed that the choice of parameters in IACS ice crushing loads for larger vessels with higher ice classes (PC1) has high uncertainty and the upper limit values are greater than those predicted by the ice mechanics approach.