ABSTRACT

This paper looks back to the early development of dynamically positioned vessels, showing how a system of suitability and safety assessment has been developed. The applications of DP have spread to a wide range of operations, and as the vessels and the systems have become more sophisticated the methods of suitability assessment have changed little, and up to now have been based upon a combination of charterers requirements and specific guidelines. The established means of assessment takes the form of a DP audit and trial, this is not a standard assessment throughout the industry, and In many cases does not take fully into account the suitability of the vessel for the work proposed, only it suitability as a dynamically positioned vessel. The current situation gives a great deal of scope for improvement and proposals outlined In this paper will give details of how a standardised system of suitability and DP safety assessment can be developed and introduced.

1. INTRODUCTION - Past to Present

Dynamic positioning systems were originally developed In the 1960's as a means of position keeping for drill ships, operating In deep waters and where it was not desirable to have mooring systems deployed. These early systems were normally developed as single computer, non-redundant facilities which In the event of a single failure would normally result In the loss of position. A large number of DP vessels at the time were not purpose built and were often converted from cargo vessels no longer fit for their purpose. As a result the DP systems which were installed had to be adapted to the design of the vessel, inheriting some of the problems which the original hull shape would produce. A major difference between a cargo ship and DP vessel is the fact that the hulls are designed for different purposes, one is designed for high speed and least resistance, whereas the other is designed to remain stationary with the minimum amount of roll, pitch and heave.

So it can be seen that from the early development of these vessels the best potential of DP system was not being harnessed. Hybrid vessels were being produced to carry out completely new work, under conditions which were highly demanding and potentially dangerous, yet the vessels were not intended nor fully tested for the purpose proposed.

During this early period, DP audits and trials were not fully developed lf at all used. As incidents occurred and more was learnt about potential hazards and failures of the systems, the need for regular audits and trials of vessels was identified. The real need for these audits and trials was only really recognised when dynamic positioning was to be used for the station keeping of dive support vessels. Prior to this development, DP vessels had only really been involved in open water drilling operations where the effects of DP failure were, at that tune, feat to be minimal and insignificant in comparison with potential drilling hazards.

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