Marine Gyro-Compasses and Automatic Pilots. A Handbook for Merchant Navy Officers

228 Pages·1964·10.6 MB·English

by  W. Burger, A. G. Corbet, J. H. Clough Smith and G. E. Earl (Auth.)

THE COMMONWEALTH AND INTERNATIONAL LIBRARY
Joint Chairmen of the Honorary Editorial Advisory Board
SIR ROBERT ROBINSON, O.M., F.R.S.
and DEAN ATHELSTAN SPILHAUS
Publisher
ROBERT MAXWELL, M.G.
NAVIGATIONAL AND NAUTICAL COURSES
VOLUME 3
General Editors
CAPT. J. H. CLOUGH SMITH, CAPT. G. E. EARL
Marine Gyro-Compasses
and Automatic
Pilots
This book is sold subject to the
condition that it shall not, by way
of trade, be lent, resold, hired out,
or otherwise disposed of without
the publisher's consent, in any
form of binding or cover other
than that in which it is published.
Marine Gyro-Compasses
and Automatic Pilots
A HANDBOOK FOR MERCHANT NAVY OFFICERS
Volume Two
Automatic Pilots
W. Burger
M.Sc. Extra Master
A. G. Corbet
Extra Master
Lecturers at the Department of Navigation
Welsh College of Advanced Technology
Cardiff
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Copyright © 1964
PERGAMON PRESS LTD.
First Edition 1964
Library of Congress Catalog Card No. 63-19534
Set in 10 on 12 pt Baskerville and printed in Great Britain by
BRADLEY & SON · GAXTON STREET · READING
Preface
THIS book is intended mainly as a reference book for Merchant Navy
Officers, but sections of it are also very useful for Officers who are studying
for their M.O.T. examinations and it is for the latter that some revision
questions are included at the end of Volume I.
The book consists of two volumes. The first volume deals with Marine
Gyro-Compasses, the second volume with Automatic Pilots and ancillary
equipment as found on most British Merchant Ships. As the majority of
British Merchant Ships are equipped with either Sperry or Brown equipment
it was felt that the book should not be extended to include the Anschütz and
Plath equipment though it is realized that many ships of other nations carry
it. The Admiralty Gyro-Compass (Sperry Type) is not discussed in this
book, but, on occasions, mention is made of it. Officers who sail with the
Admiralty Gyro-Compass are referred to the Manual of the Admiralty Gyro-
Compass [Sperry Type), London: Her Majesty's Stationery Office.
Each section of the book dealing with a particular type of compass is
something like an Instruction Manual in itself and hence a certain amount
of repetition could not be avoided in various Chapters. Two chapters are
devoted each to the Sperry Compass Mk. E. XIV and to the Brown Compass
(Types A and B) because they are still so common on British ships though
later models are, at present, being introduced all over the fleet. The lay-out
of the different chapters dealing with the actual compasses have a lot of
common features but sometimes side-steps are made in order to focus the
attention to a particular part of the equipment. This is done purely because
such a part possesses some special item of interest; it does not mean, of
course, that this part is superior in quality to similar equipment in other
makes.
For the benefit of those who want to dig deeper into the theory relating to
the gyroscope and its controlling and damping, an Appendix is added to the
appropriate chapters which, in simple mathematics, tries to explain some
concepts to the student which otherwise may always remain obscure to him.
The 85-minute period of a controlled gyroscope is a good example; without
any mathematics the explanation must remain nebulous.
An Appendix at the back of each volume deals very briefly with electrical
principles applied in gyro installations. It is not the intention to use this
Appendix as a textbook but it should form the means to find a starting point
ix
X PREFACE
from where an electrical textbook could be consulted. Most of the notes
taken during the preparation for M.O.T. examinations should also cover
this more fully. A knowledge of electrical principles is desirable for the
sequence of the switching on and off procedure and for maintenance.
Excellent five-day gyro courses are provided by the Sperry Gyroscope
Company, Limited, Brentford, Middlesex, and by S. G. Brown, Limited,
Watford, Herts. Officers are strongly advised to make arrangements with
their Company to enable them to follow the particular course (s) relating to
the type of compass carried on their ship.
This book has been built around practical experience acquired by the
authors on board ship and in running the Gyro School in the Navigation
Department of the Welsh College of Advanced Technology. It must,
however, be emphasized that the book could not have been written without
the co-operation of the Sperry Gyroscope Company, Ltd., and S. G. Brown,
Ltd., who both provided so many details and also checked the manuscript.
We thank Mr. W. H. P. Canner, Flight Lieutenant (Retd.), Flight
Navigator, for his assistance with certain parts of the manuscript.
Fuller acknowledgements and a bibliography are published at the end of
each volume.
W.B.
A.GC.
Some Advice on Reading this Book
As this book is mainly a reference book and obviously too bulky to be
read from cover to cover in a short time, it is felt that the younger officer
might need some help in planning his reading.
The student's reading is best planned from the list of contents.
The following initial reading plan is suggested:
First read the Introduction and then the chapter (s) applying to the parti­
cular automatic pilot(s) with which the officer is concerned. Next read the
sections required in Chapter XI, which deals with ancillary equipment,
and finally Chapter XIII, which gives some general remarks and advice
on automatic steering.
Introduction
AUTOMATIC steering has been devized to keep a ship heading in one particular
direction under most weather conditions. When an automatic helmsman is
correctly adjusted for the prevailing weather conditions it can usually steer
a straighter and more economical course than any human Quartermaster
—this is mainly because of the fact that the automatic helmsman cannot
daydream; its " mind " has been constructed to think of nothing other than
steering the ship.
Quartermasters have had the advantage over auto-pilots in that they can
sometimes anticipate movement of a ship about her course but, the more
rhythmic steering of the auto-pilot is a greater advantage and also, auto­
pilots which can anticipate movement have now been installed in some ships.
Figures 1 a, b and c give examples of steering under similar weather
conditions as displayed on the graph of a course l^order. Figure 1 a shows
steering by hand; Fig. 1 b steering by auto-pilot and Fig. 1 c steering by
auto-pilot with anticipation qualities.
240° 230° 220° 240° 230° 220° 240° 230° 220°
LARGER
DEVIATIONS FROM :
THE SET COURSE ;
CAUSED BY ;
SUDDEN GUSTS ! k
^ OF WIND OR i I
' OTHER EXTERNAL) ;
CAUSE I !
-ft
(a) (c)
OCCASIONAL LARGE DEVIATIONS RHYTHMIC STEERING RHYTHMIC STEERING
FROM THE COURSE OWING TO SMALL DEVIATIONS NO OSCILLATIONS
BREAKS IN THE QUARTERMASTERS OF EQUAL AMPLITUDE. AS IN (b).
CONCENTRATION.
FIG. 1. Comparison of steering methods
XI
XU INTRODUCTION
The complete action of steering will now be considered. When the ship's
head swings off course, say to starboard, the quartermaster applies port
helm to bring the ship's head back towards the course. As the ship's head
starts to swing back the amount of port helm is decreased and then the helm,
perhaps, put to midships when the ship's head is back on course or, if need
be, counter helm to starboard is applied to check the ship's head and
prevent it swinging on past the course to port.
At the end of his trick on the wheel the quartermaster states the course
and usually gives some guidance to his relief. For example, he might say
" She's swinging about two degrees on each side of the course and taking
about three-quarters of a turn to starboard and half a turn to port ".
Perhaps, instead of giving the number of turns of the wheel each side he
may give the actual rudder angles, for example, 10° to starboard and 7° to
port.
In more technical terms it could be said that the ship was carrying 3°
starboard helm or rudder (10°-7°) and yawing 4° (that is, two degrees each
side).
The helm may be carried either because of transverse thrust from the
ship's propellor(s) or because of a combination of transverse thrust and
weather conditions. With a single right hand screw propellor a ship's head
tends to turn to port when going ahead. When the wind is on the port bow
of a ship with a large forecastle head and " flying light " the ship's head
tends to fall to starboard away from the wind. On the other hand, a ship
with a high superstructure ait tends to head up into the wind. Thus the
amount of weather helm carried depends on individual ship characteristics
and the prevailing weather conditions.
Yaw is caused mainly by swell. The amount of yaw experienced depends
on the amplitude of the swell and, more important, the direction of the
swell in relation to the ship's head. For instance, a heavy head swell should
hardly cause a vessel to yaw at all, although she may pitch a good deal.
Similarly, a heavy beam swell should not cause the vessel to yaw although
she will probably roll heavily. On the other hand, a moderate swell which
approaches the vessel on either bow or quarter will probably cause the
vessel to yaw on either side of her course no matter how skilled the quarter­
master. In fact, the over-zealous quartermaster who attempts to prevent
yaw is generally putting unnecessary wear and tear on the steering gear.
In general ships tend to yaw most when the swell is approaching from
about four points abaft the beam. The action when a swell approaches from
abaft the starboard beam is first for the swell to catch the stern and throw it
upwards to port thus swinging the bow to starboard; as the swell overtakes
the vessel the stern falls down into the following trough and the bow is
lifted and thrown back to port. The cycle is then repeated. If the vessel's
INTRODUCTION xiii
speed and course are such that the crest of the swell catches the stern at the
same time as when the bow is in the trough the ship will yaw considerably
—a synchronism being established between the period of yaw and the
apparent period, i.e. the period of encounter, of the swell. There could also
be a synchronism between the natural period of the ship's roll and the time
between successive wave encounters of the swell. This would cause the ship
to roll violently and could be dangerous. This latter type of synchronism
should be avoided whenever possible and can be broken by an alteration of
course and/or speed in order to change the period between successive wave
encounters.
The sensitivity of a quartermaster's steering is inversely proportional to
the amount of yaw, that is the greater the yaw the less sensitive the steering.
If, for example, a ship is yawing two degrees (one degree on each side of the
course) the quartermaster will only change the amount of helm he is
carrying when the ship moves more than one degree off course.
In general, in calm weather or with wind, sea and swell ahead it is usually
found that a vessel is best steered with small, sensitive helm applications and
with little, if any, weather helm being carried. In heavy weather with the
vessel yawing it is found that larger, less sensitive helm applications are
required. The amount of weather helm, as mentioned earlier, depends
on the characteristics of the ship and the directions of the wind, sea and
swell.
Automatic helmsmen are provided with controls for adjusting the amount
of rudder, yaw (sensitivity) and the amount of weather helm carried. The
degree of success of the automatic steering depends on how well the officer
on watch can make these adjustments according to the prevailing weather
conditions and the characteristics of the ship.
The automatic helmsman receives information about the direction of the
ship's head from the transmitting system of a gyro compass or, in some cases
lately, from a transmitting magnetic compass. This generally means that an
actual alteration of course has to occur before rudder is applied or removed.
A human quartermaster can often harmonize himself with the helm in such
a way that he can anticipate the moment when the ship is about to fall off
course and thus apply helm in anticipation of this movement. Some later
types of automatic helmsmen have a time adj ustment fitted which enables
the rudder to be applied or removed before the ship's head actually moves
and can thus " anticipate " movement—compare Figs. 1 b and 1 c. The
setting of this adjustment is again the responsibility of the officer on watch
because it depends on the prevailing conditions.
One of the main objects of this volume, besides providing an explanation
of the working and information about the maintenance of various types of
auto-pilots, is to assist the officer in making the above important adjustments.
XIV INTRODUCTION
Types of Automatic Steering
The first types of automatic steering utilized the ship's existing bridge-to-
rudder transmission systems, that is the telemotor system or rod and chain
gear. This was done by connecting an electric motor to the shaft of the
normal hand steering wheel on the bridge. The electric motor was housed
together with the control unit adjacent to the hand steering wheel and the
connection between the electric motor and wheel shaft was in the form of
either a chain and sprocket or a worm wheel and worm drive. The electric
motor and wheel turned in response to electric signals from the control
unit. A clutch was used to disconnect the electric motor from the wheel
when ordinary hand steering was required.
The above system worked reasonably successfully, but was rather sluggish
and more direct means of transmission from the control unit to the steering
gear have been developed which give much better results.
There are now two basic systems of automatic steering which may be
simply referred to as the single unit system and the two unit system.
The single unit system is used with all-electric steering gear. In this case
the electrical output signals from the single (bridge) unit are fed directly to
the electrical steering gear.
The two unit system is necessary when the steering gear is a type which
is operated mechanically, that is, by a lever moving a control valve. The
electrical output signals from the bridge unit must be converted into
OFFICER ON WATCH
WEATHER AND SHIP
CHARACTERISTICS
Hi
BRIDGEj
Y//7A
FEEDBACK
INFORMATION
FROM THE ' ELECTRICAL
STEERING GEAR • OUTPUT FROM
BRIDGE UNIT
JELECTRICAL
CONTROL I
STEERING
GEAR
(ELECTRIC)
FIG. 2. Schematic diagram showing the general arrangement of the single
unit system