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.

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.

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

,,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.

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.