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Abstract

Shiphandling tugs are a critical aspect of ship manoeuvring in confined waters.
Knowledge of their performance and effective use in various situations provide
necessary guidance for the marine pilot and tug master to improve shiphandling
techniques. Shiphandling simulators are a well accepted tool for training of marine
pilots, development of port operational procedures and port development studies.
Realistic simulation of shiphandling manoeuvres requires not only a reliable
hydrodynamic model of the ship, but also precise representation of the forces
available from the assisting tugs.
In the past, the limited capabilities of tugs meant that force prediction and evaluation
of operating procedures was a relatively simple matter. However, the push for
expanding and more efficient port operations has led to a new generation of
shiphandling tugs being introduced into major Australian ports during the 1980's.
These tugs are of greater displacement, power and manoeuvrability compared with
their twin screw predecessors and represent a significant technological step.
Increased manoeuvrability of the so called omni-directional stern drive tug has been
achieved through the fitting of azimuthing thrusters, which are capable of producing
thrust in any direction. The enhanced manoeuvrability of the omni-directional stern
drive tug and increased power has enabled significant increases to be made in the
efficiency of shiphandling operations, particularly in the ability to assist at speed.
However, to fully realise the potential of these complex vessels a more thorough
understanding of their hydrodynamic aspects is required. Further, with increased
speed greater consideration needs to be given to the interaction of tug forces with
those produced by the ship's rudder, propeller and hull.
To investigate the performance and effectiveness of omni-directional stern drive tugs,
a series of physical model tests has been performed. Hydrodynamic forces acting on
the hull and thrusters have been measured, with particular attention being paid to
hydrodynamic interactions between thrusters and the thrusters and hull.
Measurements were initially made of forces acting on a bare tug hull and a single
thruster in open water. Thruster-thruster interaction was determined from
measurement of forces acting on twin thrusters in open water and thruster-hull
interaction was determined from measurement of total forces and those acting on the
thrusters of a self-propelled free-running model.
Data derived from the model tests has been used to construct a mathematical model
which may be solved using equilibrium or, in the time domain, as may be desired for
real time simulation. Quasi-steady predictions of tug forces have been used to
identify general performance, optimum operating techniques and the influence of tug
forces on ship motions in confined waters. In cooperation with Australian towage
operators, practical findings from this investigation have been detailed in a manual to
assist tug masters and marine pilots.
In addition to harbour tugs, this work may also provide insight into the manoeuvring
of escort tugs and other vessels with omni-directional propulsion.

Item Type:	Thesis - PhD
Authors/Creators:	Brandner, Paul Anthony
Keywords:	Tugboats, Ship propulsion
Copyright Holders:	The Author
Copyright Information:	Copyright 1995 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Investigates the performance and effectiveness of omni-directional stern drive tugs through a series of physical model tests. A mathematical model has been constructed using data derived from the model tests, and practical findings detailed in a manual to assist tug masters and marine pilots. Thesis (Ph.D.)--University of Tasmania, 1997. Includes bibliographical references. Investigates the performance and effectiveness of omni-directional stern drive tugs through a series of physical model tests. A mathematical model has been constructed using data derived from the model tests, and practical findings detailed in a manual to assist tug masters and marine pilots
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