Abstract

This paper specifies the operational requirements for a ship-based sensor system for reliable all weather detection and avoidance of ice obstacles for two applications:

  • for station keeping at northerly dri11sites and production sites;

  • for large, high-speed LNGC's as planned in the Arctic Pilot Project.

In application i), development of reliable detection and diversion techniques for icebergs has important implications for the feasibility and design of completion systems. In application ii), maximum reliable detection range is an essential parameter for determining the maneuverability requirement and hence the overall configuration of LNGC's, as well as determining their maximum safe operating speed and hence LNG shipment costs.

Radar, sonar, IR, and low-level light detectors are analyzed for their detection capability. Each sensor is discussed in terms of the transmitting channel or medium and ice target characteristics peculiar to that sensor, including dependence of target strength on berg size and shape.

The capabilities and deficiencies of currently available sensor hardware are discussed, both separately and for use in mu1tisensor systems. Finally a field program to obtain sensor parameters is briefly reviewed.

Introduction

Icebergs have posed a hazard to navigation at least since the establishment of trans-Atlantic shipping lanes across the Grand Banks east of Newfoundland and through the Strait of Belle Isle, a hazard which was dramatically realized with the sinking of RMS TITANIC by an iceberg in fog on April 14, 1912 at 41 °40'N, 50° 03'W. Since then, the International Ice Patrol (organized by the U.s. Coast Guard) has provided information about iceberg movement in the vicinity of Newfoundland. This data, together with operating procedures for ships in ice that include reduced speed and strict radar and visual watches, has kept subsequent incidents to a minimum.

However, the opening-up of the Canadian East 'Coast and Arctic areas for oil and gas production and transport will find current procedures either unduly constraining and hence costly, or simply insufficient. This motivates improvements in equipment and even a complete rethinking of the problem.

The iceberg problem for oil and gas development on the Grand Banks is summarized by Reference 1. While icebergs are heavy on the Grand Banks only for three months, April, May, and June, at the north of Labrador and in the Davis Strait they arefound usually fairly thick for nine months of the year. Peak densities are higher in the north, and the bergs on average are larger

Terminology

It is useful to distinguish several size classes for icebergs

  • Iceberg:Massive piece of glacial ice with a sail height of more than 15 ft.

  • Comparable in above-water size to a large merchant ship. Mass upwards of 5400 tons

  • Bergy Bit: Large piece of floating glacial ice, comparable in above-water size to a small house. Mass 120-5400 tons.

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