Abstract

This paper describes the practicalities and principles of use of icebreakers in support of ice offshore operations, and specifically their efficiency in support of vessel shape floating platforms in ice. All information in this paper is bsed on real life experience in some key operations with such platforms with ice management. The paper also summarises the similarities and differences between traditional icebreakers and new technology representing icebreakers which are equipped with azimuth thrusters. It discusses the influence of support icebreakers and their function in the design and practicality of operations of floating offshore platforms, resulting form use of supporting icebreakers. It also gives general indications of the achievable levels of operability with various levels of ice management in a wide range of effective ice thickness. A multitude of practical applications for ice support vessels and the natural, multiple roles for such vessels are described.

Background
Ice offshore operations and ice management

The oil industry these days is increasingly orienting its interest towards ice covered waters. The planning for this, especially in water deeper than about 100 m, utilizes various vessels such as drilling platforms or FPSOs, with icebreakers in support for their station keeping. The use of icebreakers enables stationary operations in ice to continue into increasing degrees of difficulty. Fortunately there is significant background experience with stationary ship operations in moving pack ice which has been performed since the seventies and increasingly in the last several years. These operations have introduced a whole new way of operating vessels in ice. The utilization of vessels in such ice offshore operations is substantially different as well as more demanding than the traditional ice transit operations or port operations in ice covered ports and terminals.

The objective of traditional ice transit operations is to maximize transit efficiency by intelligent navigation and by focusing on ice avoidance and specifically avoiding the need to penetrate the most severe ice features. This results in the most efficient performance transiting from point A to point B in ice covered waters. Ice offshore projects, which operate in moving pack ice, have an objective to ensure that station keeping operation can continue with a high degree of confidence that the station keeping limits of the floating platform will not be exceeded. To achieve this the ice offshore project needs rigorous risk control to ensure that all operations can be stopped and the platform can be removed safely from the location. A highly demanding aspect of this operation is that it requires high confidence in the capability to stay on location before such operation is justifiable. These altered requirements lead to new roles for icebreakers in the supporting operations of such ice offshore projects. The mission is now to find the most severe ice and break it. Not only is it required to be found, but also the severity of approaching ice must be defined in terms of the ability of the support icebreakers to break it to a sufficient degree that a stationary platform can stay on location.

Ice management in support of stationary operations with vessels covers the approach and full logical sequence for providing the safe operation and safe exit when required. The total scope of ice management is actually called more accurately " risk management for ice offshore operations??. This includes the physical ice management with icebreakers or to any degree that may be applicable, self ice management techniques. However, before any of the physical ice management takes place, the following needs to happen as an integral part of the ice management:

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