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- D O E R F F E R ' S - R U D D E R -
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TECHNICAL UNIVERSITY OF GDANSK OFFERS:
- designs of this novel type of rudder for all types
and sizes of ships to the requirements of any Classification
Society;
- working drawings and material specifications;
- inspection during manufacturing of individual parts
and during assembly of same and rudder on board;
- participation in harbour and sea trials of the ship;
- inspection of the rudder in service.
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Doerffer's Rudder"
has been fitted so far aboard four ships: |
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Manoeuvrability, braking
efficiency and course control while braking are of primary
importance for the safety of navigation of all types of
ships.
A new opening rudder, called "Doerffer's Rudder"
from the name of its principal designer, has been developed
at the Ship Research Institute of Gdansk Technical University
as a result of attempts to improve manoeuvering and braking
characteristics of ships.
Two coaxially mounted rudder blades with movable flaps
on the trailing edge are independently powered by two
steering engines. The propeller wake can be redirected
forward to P and S depending on the manoeuvre.
Three working modes are possible:
1. with joined blades it behaves similarly to a conventional
rudder;
2. with the asymmetric opening angle, large side forces
allow to manoeuvre effectively in narrow waters even at
speeds nearing zero, to turn close circles, etc.;
3. with large symmetric opening angles to both sides it
is possible to create large forces essential for braking
and backing the vessel. Braking distance may be shortened
by at least 50% in comparison with that of the classic
..crash stop" manoeuvre. Control and correction of
the course is at all times possible. Astern speeds up
to five knots with propeller working forward are obtained.
"Doerffer's Rudder" could be fitted on any
type of new or existing ship. All the manoeuvres can be
executed by means of a joystick at constant propeller
speed. Alternate steering systems are possible. These
systems are designed and produced by the well known Polish
marine & aircraft equipment manufacturers - Wytwornia
Sprzetu Komunikacyjnego ,,PZL Warszawa II".
They are designed to match full manoeuvring and braking
potential of the rudder, offering a hand follow-up and
non-follow-up steering as well as autopilot. An option
with a computer aided manoeuvre execution (CAME) is also
available, which makes an optimum performance obtainable
even without high skill operator of the system. For hand
steering a selection of controls is being offered: joystick,
double coaxial lever control,
push button control plus joystick, watertight open deck
additional controls. Also gyrorepeaters and rudder angle
indicators are available. A typical lay-out is shown below. |
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1. Autopilot and follow-up computer
2. Joystick of follow-up steering
3. Non-follow-up control (push buttons)
4. Supply and connection box
5. Feed-back transmitters of the port and starboard
rudder blades
6. Output control signals to a rudder gear control solenoids
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,,Doerffers Rudder" consists
of a fixed forward part and a swinging after part divided
in the plane of symmetry into two, coaxially mounted blades,
which can be activated independently to an angle of -25°
to +75°. A vertical flap is fitted on the trailing
edge of each blade, which can be deflected to an angle
of 90°. Internal and external rudder stocks are necessary
for independent activation of rudder blades by two steering
engines.
The flaps are activated by fixed length stays proportionally
to the angle of blade opening or independently by hydraulic
power hinges or jacks, thus they could be used for minor
course corrections without activating the main steering
engine.
Such an arrangement enables perfect con-trol of speed
at constant forward revolutions of the propeller from
maximum forward to maximum astern, just by chan-ging the
symmetrical angle of rudder blade opening from 0°
to 75°(vertical curve).No reversible propeller is
requi-red. During braking and astern move-ment the vibrations
are considerably re-duced and a perfect course control
is obtained.
At asymmetrical opening of rudder blades a considerable
side thrust at zero speed could be developed, safeguarding
perfect manoeuvrability at harbour speeds with the diameter
of circulation equal to zero. At service speeds the diameter
of circulation is greatly reduced with the ship practically
turning in circles round her midships after a very short
advance. Thus the rudder could be used as a powerful stem
side thruster. |
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ADVANTAGES
OFFERED BY ,,DOERFFER'S RUDDER"
- Proper hydrodynamic design of the rudder and of end
plates allows better extraction of propeller wake
rotational energy, thus increasing the free running
speed and the bollard pull of the ship;
- improved course stability, while running free and
towing;
- full compliance with the IMO requirement for the duplication
of steering power units on certain types of
ships above certain size;
- turning ability of a ship with blocked rudder blades,
activated by one steering engine to an angle of 25°
is
at least the same as with the balanced rudder under
38° inclination;
- largely improved stopping ability with full course
control;
- great reliability of all manoeuvers, because no stopping,
reversing and starting the main engine is
required;
- no reversability of the main engine or the reduction
gearing is required. Simple reduction gearing costs
about 30 to 40% less and has smaller dimensions and
weight. In case of steam turbine drive no reverse
turbine is required;
- shaft generator could be working during manoeuvres
as the shaft revolves at a steady number of
revolutions;
- lower maintainance costs of the main engine due to
running at a steady rate constant parameters;
tow line is prevented from fouling the propeller;
- for ship positioning the ..Doerffer's Rudder"
could be used as stem side thruster.
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GDANSK UNIVERSITY of TECHNOLOGY, FACULTY
OF OCEAN ENGINEERING & SHIP TECHNOLOGY,
DEPARTMENT of SHIP DESIGN and SUBSEA ROBOTICS
80-233 Gdańsk, ul.Narutowicza 11/12, Poland
ph. (48 58) 347 19 91, fax: (+48 58) 347 26 99, e-mali: sek8oce@pg.gda.pl
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