ABSTRACT

Developments now taking place in the northern North Sea all point to the laying of pipelines in this area for the transportation of oil and natural gas; this has led to the blue-printing of a radically new concept for a deepwater lay barge designed to lay pipe in heavy sea states and at laying speeds appreciably higher than those commonly in use today.

Significant features of the new design are a large semi-submersible hull; a stern ramp for launching the pipe and integrated into the barge design; and a 14-point mooring system controlled by a single operator, but with design features for subsequent full automation. The paper describes these and several other revolutionary features of the barge, and discusses the typical problems encountered in the construction of the large hull.

INTRODUCTION

Pipelaying offshore is gradually moving into deeper and rougher water so that conventional laybarges are almost reaching their capability limits, not only in water depth, but also in sea states. While the challenge to lay pipe in rough and deep water has always existed, in the northern North Sea what was earlier a challenge is now evolving into a necessity as new discoveries of major oil and gas fields are made. By 1979 at least 1.000 miles of pipelines will have been laid in this area (ref. 1). A substantial portion of this mileage will be laid in water depths greater than 400 ft. To achieve this, laybarges will have been exposed to the harrowing combination of long Atlantic swells and the frequent and severe storms common to the northern North Sea. The combination of bad weather and good industrial prospects has inspired a group of European companies to pool their knowledge and resources to develop a new and radical approach to pipelaying in deep water.

Viking Jersey Equipment Ltd., which represents the collective interests of the group of companies, has acquired the design rights to a large, recently designed semi-submersible lay-barge which incorporates several unique features. This paper not only describes the salient features in the design of this unique piece of equipment, it also deals with the construction of some of the major items.

On November 1, 1972 Viking Jersey Equipment Ltd. awarded the building contract to IHC Gusto of Schiedam. Pipelaying with the new equipment is scheduled to commence early in 1975.

WHY A NEW GENERATION OF PIPE LAY-BARGE?

The most widely used method today of installing offshore pipelines is by lay-barge; the prototype of present vessels was developed and first constructed in 1956. The ‘L.E. Minor ’, the prototype vessel, installed the world's first major offshore pipeline off Cameron, Louisiana, for the Tennessee Gas Transmission Company. Since this first vessel went into operation, very few changes have been made to the original laying technique.

At the present time more than 40 offshore lay-barges of conventional design are in use; their length ranges from 350 to 400 ft and their width from 65 to 120ft. An 8 or 10 point mooring system is most commonly used, and nearly all barges have pipe tensioners and stinger systems.

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