Причины различий между коэффициентами упора винта при работе за корпусом судна и в свободной воде на швартовых

Abstract

Object and purpose of research. The object of research is the results of self-propelled ship tests in bollard-pull conditions. The purpose is to analyse the hydrodynamic sources giving rise to differences between propeller thrust coefficient in open-water and behind-hull conditions. Materials and methods. Analysis based on the ideal propeller theory shows that the velocity ΔV of inflow on propeller operating behind ship hull in bollard-pull conditions caused by a system of sinks, ensuring flow attachment to hull surface, has a finite value and is actually the effective wake. The wake velocity for an open-water propeller is equal to the behind hull velocity. The open-water propeller thrust coefficient at advance ratio (formula) is due to the opposed jet of its reversal. It is shown that the thrust coefficient deviations at self-propelled tests in open-water has to do with the specifics of propeller thrust variations in the operating area adjacent to bollard-pull conditions. Boundaries of the operating area where the opposed jet affects the propeller curve at self-propelled tests are defined. Practical conclusions and recommendations are given following from the obtained data. Main results. The source of discrepancies between self-propelled test results for open-water propeller in bollard pull conditions and close operating area has been found. Recommendations are given on updating the test procedures for propeller and self-propelled model tests Conclusion. The paper is expected to be useful for understanding the ambiguity of self-propelled test results.