Determination of meridian position by a two-step ground gyrocompass in eesthetical rotor positioning

Contradiction between accuracy and time of definition of a plane of a geographical meridian has significantly weakened with appearance of automatic gyrocompasses and algorithmic methods of processing of the information from them. These methods allow us to expand the range of possible modes of gyrocompasses, including non-traditional. The article considers an automatic two-stage ground gyro compass operating in the mode of natural stopping of the rotor after its pulse acceleration by non-electrical means (squib , compressed air, etc.). The specified mode is attractive because it allows to identify uncontrolled harmful moment around the axis of suspension in one start and significantly reduce the measurement time. In order to further improve the device, it is proposed to abandon the measurement of the current value of the kinetic moment, and to identify the decay coefficient of the exponential function by observing the azimuthal motion of the sensitive element of the device. Moreover, the paper shows that it is possible not to measure the initial value of the kinetic momentum, replacing the measurement with identification of this parameter by observing the same azimuthal motion of the sensitive element. In this case there is no need to have on the sensitive element any nodes associated with the transmission of power and electrical signals, the sensitive element can be made as a purely mechanical element, carrying on itself a rotating rotor. For all considered variants of measurement (or identification) of parameters the machine simulation was carried out, which confirmed the performance of the proposed methodology.

Application for Simulating Gyro-Compass Behavior

Resolution of International Maritime Organization (IMO Res. A.424 (XI)), International Convention for the Safety of Life at Sea (SOLAS V/19.2.5) and consequently ‘Provisions Survey of Ships Marine’, part V, contained in the Polish Register of Shipping impose an obligation to fit ships with gyro-compass as one of the most complex marine equipment has found in the curricula of seafarers at the operational level (IMO Model Course 7.03). Curriculum involves the use real navigation devices. In addition, the adaptation of teaching facilities to meet the needs of the training process often requires the development of educational aids in the form of simulators and applications that represent the construction and operation of navigation devices. The article presents possibilities of the application - gyro-compass simulator developed for the requirements of the Institute of Navigation and Maritime Hydrography PNA. Among others, the program is used to simulate the conditions in which you can expect the occurrence of different types of gyro-compass deviation. Designed software is expected to improve the educational process, to help the students assimilate the content of the curriculum in the field of classic gyro-compasses and familiarize trainees with static and dynamic errors occurring with the change of operating conditions.

Dynamic Positioning System for a Ship on Harbour Manoeuvring with Different Observers. Experimental Results

In cases when the navigational space of the manoeuvre performed by the ship is severely limited, the procedures making use of the rudder blade, propeller screw, and thrusters are very complicated. Such situations take place when the ship manoeuvres inside the harbour area and in those cases the structure of the control system is very complex. Te article describes the algorithm of multivariable control of ship motion over the water surface, which makes use of the state vector consisting of 6 variables. Tree of them, which are the position coordinates (x, y) measured by the DGPS system and the ship heading y measured by gyro-compass, were obtained experimentally. Te three remaining variables, which are the velocities in surge u, sway v, and yaw r directions, were estimated by Kalman filter, Kalman-Bucy filter and extended Kalman flter, respectively. The control algorithms making use of these observers were examined using the training ship “Blue Lady” which was navigated on the lake Silm in Ilawa/Kamionka in the Ship Handling Research and Training Centre owned by the Foundation for Safety of Navigation and Environment Protection. Te experimental results obtained using control systems with three observers were finally compared between each other.

Keith Richard Greenaway

Keith Richard Greenaway, who died on 21 May 2010, aged 94, established himself early in his career as the pre-eminent authority in north America on Arctic air navigation. He was only a flight lieutenant, RCAF, with 11 years service when he published his Arctic air navigation (1951), which immediately became the standard textbook in its field. The book deals with all aspects of air navigation, bringing information scattered in various publications together with the author's already very wide practical experience. The heart of the book details the limitations of the magnetic compass in high latitudes and sets out procedures in the reliable Asco-Gyro system of navigation, which Greenaway did so much to develop and which involves the determination of aircraft heading by astro compass and the maintenance of direction by gyro compass, continuously corrected for gyro-drift.

Use of GPS-Determined Attitude in Combination with Conventional Attitude Sensors

Use of multi antenna GPS equipment for determination of a vessel's attitude holds some promise for the development of accurate and inexpensive attitude systems. An application for such systems might be to provide very accurate roll information for multibeam echo sounders.The present state-of-the-art GPS attitude systems cannot meet the required accuracy and update rate for such applications. GEOTEAM A/S has therefore developed a PC-based system which combines GPS-based attitude with roll and pitch information from a Vertical Reference Unit (VRU) and heading from a gyro compass.In such a combined system, the long-term high accuracy of a GPS-based attitude system is combined with the short-term accuracy and fast update rate of conventional VRUS and gyro compasses in order to achieve a resulting performance that is better than any of the systems. In effect, the GPS attitude is used to calibrate the VRU and the gyro compass in real time.During the past year extensive tests have been performed with a system using a Trimble VECTOR II GPS attitude system with a 1 metre baseline between the antennas, both on a van (with an inertial navigation system as reference) and on a vessel. During November and December 1993 further tests were made with an Ashtech 3DF attitude system with longer baselines (7·5 m). These tests were made on a vessel where the combined GPS/VRU attitude was fed into a multibeam echo sounder. These tests were performed in cooperation with Simrad Subsea A/S, the multibeam echo sounder EM 1000 manufacturer.

A Polar Compass

The basic premise of compass adjusting (that is compensation aboard ship for magnetic fields caused by the vessel itself and the determination of residual deviation) is that a reference direction must be available during the operation. Normally visual ranges or the azimuth of a celestial body—usually the Sun—are used, but in some areas and climates reduced visibility often does not permit the use of either. Compass adjusters are frequently driven in desperation to use gyro-compass, radar, or radio bearings—with highly speculative results as the errors of these instruments are generally unknown, and fairly large compared to the accuracy required of the magnetic standard compass (± ½°) which is the primary direction standard aboard ship.