The R. V. Polarstern carried out ice breaking trials in which ice forces were measured with special panels at two locations in the bow. Time series records of the ice forces for a 13-minute period were compared for differences in terms of magnitude and duration of loading for the two locations. Maximum force of 2800 kN was measured on a 1 m2 panel. The nature of ice forces measured on the panels was very different in terms of frequency and duration compared to those measured with strain-gauged frames on the R. V. Polarstern and the CCGS Louis S. St-Laurent.
A ship navigating in ice-covered waters will interact with ice, generating forces. This is a process where the ship and the ice interact with each other. A good overview of the issues can be found in Kujala (2017). The forces measured depend on a number of factors, such as ice thickness, floe size, ice type, ice strength properties, ship speed, ship structure, hull form, and the measuring system itself. Various types of instrumentation have been used to measure ice loading on vessel hulls. This has included strain gauging of the hull structure itself, i.e., frames and plates and application of an influence matrix to convert the measured strains to ice forces. With multiple strain gauges, a relatively large area can be covered and force distribution within the area determined. Examples include the USCGC Polar Sea where a 9 m2 area of the bow was subdivided into 60 sub-areas, each 0.15 m2 (St. John and Daley, 1984), the CCGS Louis S. St-Laurent with a 14 m2 area divided into 15 sub-areas of 0.75 m2 (Ritch, 2005) or recently the Frij with 9 m2 divided into 36 sub-areas of 0.24 m2 (Piercey et al., 2016). To determine forces on smaller areas, bending strains in plates over smaller framed areas were employed and one of the smallest was 8 mm dia. (Glen and Comfort, 1983). Interpretation of measurements on plates, particularly when they are larger than 0.1 m2, are dependent on the distribution of ice forces on the plate. A different approach has been to use load cells for direct force measurement on an isolated section of hull. This approach provides a direct measure of the total ice force on the area, independent of distribution. Normally the measurement areas have been limited in size, and substantial modifications to the hull structure are required to accommodate this approach. An implementation of this approach was on the R. V. Polarstern where areas of 1 m2 were implemented. The hull structure of the R. V. Polarstern was also strain gauged. This paper will describe some results of the two measurement approaches on the R. V. Polarstern, comparing them with each other and also with strain-gauged-based measurements on another ship.
