Analytic representation of the propeller thrust for modelling ship manoeuvring within an ice channel behind an icebreaker

Abstract

Navigation of cargo ships using icebreaker assistance is a common tactic in difficult icy conditions. The icebreaker makes the ice channel and the lone cargo ship, or the convoy, sail within the channel it has made. When the icebreaker or the vessel ahead stop before the insuperable ice obstacle, the danger of an emergency appears, namely, the collision with an icebreaker or the ship ahead, if the interval between them is not sufficient for effective braking and stopping, or for a way out in compact ice cover. To find the safe interval recommendation, it is necessary to carry out modelling of the ship manoeuvring: either braking or the leaving of the channel. In these modes of ship movement, the propeller operates in unusual modes: in reverse mode when braking, and in close to mooring mode when leaving the channel, which do not have analytical descriptions because of the detached flow of the blades. This paper describes a developed empirical method for the parameterization of the propeller thrust coefficient dependence upon the advance, based on diagrams for the design of the propellers, which were created from the test material of the serial propeller tests. Outcomes of the investigation will be applied for computer modelling of the ship's manoeuvring within the ice channel and the safe interval between the ship and an icebreaker evaluation in what follows.

Keywords

• Ship braking
• Ice channel
• Propeller thrust
• Advance
• Action curve
• Reverse and near-mooring regime