ABSTRACT

Polar ships, eventually, need the assessment of their performance both in open and ice-infested waters. The authors carried out performances evaluations of a polar carrier in open and ice-infested waters and icebreaking capability in the three cases of its propulsion scheme, i.e. fixed pitch propeller (FPP), controllable pitch propeller (CPP) and duct propeller (DP), and then compared their performances. Lifting surface theory was applied to estimate their optimum propeller parameters such as diameters and pitch ratios, etc. The delivered power in full scale was estimated by the balance of net thrust of propeller and resistance of the ship, where interactions between ice and propeller and suction effect of propeller behind the ship were taken account. The icebreaking capability and power performance were derived from an interpolation method based on given powers of the main engine. The comparison of the performances indicated that DP scheme had the highest icebreaking capability. On the other hand, it presented the worst performance in open waters among the three propulsion schemes.

INTRODUCTION

Power performances are substantially different between the conventional ships and the polar ships, due to the marked difference of navigation conditions between them. At present, taking account of the case when a ship is trapped in ice, ship owners would prefer a pod type propulsor to conventional ones for polar navigation, as a result of its high manoeuvrability and excellent icebreaking capability. However, its high cost often decreases their desires for the pod propulsion, and as consequence, they adopt the conventional ones for polar ships.

The authors carried out performance evaluation of a polar carrier in open and polar waters and icebreaking capability in three cases of its propulsion scheme, i.e, fixed pitch propeller (FPP), controllable pitch propeller (CPP) and duct propeller (DP), and compared their performances. Firstly, the propulsion performances of these propulsion schemes were analyzed. Secondly, structure strength of the propulsion schemes was checked according to the regulations of a classification society. Finally, comparisons were made of the power performances between three propulsion schemes, by carrying out calculations in detail, which will hopefully provide a good reference for ship owners. In this study, the effects of flexural strength of sea ice could not be examined.

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