A semi-empirical pod model for USCG icebreaker mackinaw. Part II. The model

A semi-empirical pod model is developed based on experimental data for the USCGC Mackinaw to predict propulsion forces for the icebreaker driven by twin podded propulsors. The experiments are conducted in straight-ahead motion with the azimuth angle of one of the twin pods steered in a range from 0 to 180o. In this pod model, assumption was made to extend the test data to the full range of 360o azimuth angles and advance coefficients. Since all the tests are carried out in straight ahead motion only with a constant heading, analysis was performed to extend these functions to general cases of arbitrary planar motions. Three pod models were presented with varying degrees of complexity. Model I is the simplest model, applying the nondimensional longitudinal and transverse force coefficients obtained from the straight-ahead motion at known advance coefficient and azimuth angle directly to any motion. In Model II, the influence of geometrical drift angle local to the pods is added to Model I. In Model III, the influence of hull-pod interaction on the geometrical drift angle is added to further refine the model treatment. These models are implemented in the NRC/OCRE-RC\u2019s in-house maneuvering simulation software OSIS-IHI and their validity assessed. The comparison of Model III with comprehensive model test and limited sea trial data shows good agreement. Based on the validation results, it is concluded that the final model (Model III) can be used successfully for motion simulation of pod-driven ships.Peer reviewed: YesNRC publication: Ye