Measurement of the Position of the Vessel
One of the simplest methods of determining the position of the vessel relative to the sea-bed is by means of a taut wire stretched between the vessel and a weight on the sea-bed.
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JOHANNES PINKSTER NETHERLANDS SHIP MODEL BASIN, WAGENINGEN
DYNAMIC POSITIONING OF VESSELS AT SEA
COURSE HELD AT THE DEPARTMENT OF EXPERIMENTAL METHODS IN MECHANICS OCTOBER urn
UDINE 1971
SPRINGER-VERLAG
WIEN GMBH
This work is suliect to copyright AU rights are reserved. whether the whole or part of the mllterial is concerned specifically those of translation. reprinting, re-use of illustrations, broadcasting, reproduction by photocopying machine or similar means, and stor. in data banks.
© 1972 by Springer-Verlag Wien Originally published by CISM, Udine in 1972
ISBN 978-3-211-81221-1 ISBN 978-3-7091-2983-8 (eBook) DOI 10.1007/978-3-7091-2983-8
PRE F ACE
In the following a brief review is given of the origin of dynamic positioning as a means for station-keeping.
The main elements which make up
such systems are discussed as are the main sources of the disturbing forces. The most important properties of any st£ tion keeping system are those of static and dynamic stability about the equilibrium position. These are discussed for a simple case of dynamic positioning. With the aid of a numerical example it is shown that for this simple case 3 linear theory yields results which point to an optimum position of the lateral thruster.
J.
Pinkster
1. INTRODUCTION The discovery in recent years of vast miner3l deposits on and below the floors of the seas and oceans has resulted in a great increase in the number of offshore mining projects. Allover the world companies are engaged in the
dri~
ling of wells the laying of submarine pipelines and the recovery of valuable minerals such as diamonds and even gravel and sand from the sea-bed. In deep sea these activities are carried out from surface vessels. The type of vessel used for this work ranges from plain barges to intricate and costly designs as the semisubmersibles. Common to practically all activities concerned with the exploration and exploitation of the sea-bed is the necessity of accurate positioning of the vessel relative to the point of interest on the sea-bed. An
example showing the need for accurate posi-
tioning of the surface vessel in the case of a drilling vessel. (See Fig. 1). In this case the drilling vessel from which the drill string reaches tv the well on the sea-bed, must remain within well specified limits of the point of intersection of the horizontal plane coinciding with the surface of the sea and the vertical line reaching upward from the well. Failure
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Introduction to remain within these limits will, and has in the past, resulted in fracturing of the drill string. It may be noted that the heading angle of the drill-ship is of sec ondary importance. Another example illustrating the need for good station keeping abilities Fig. 1
is that given in Fig. 2.
This shows, schematically, the effect of errors in the co-ordi nates in the horizontal plane and heading angle of a pipe-laying barge on the loading of the pipe. In comparison with the previous example the demands placed on the station keeping
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