Electromechanical System for Determining the Position of the Ship

Recently more and more activities performed on the sea require keeping the ship on the same position ? dynamic positioning. The most common method used for the position determination is by applying GPS device. However, on the Earth's geographical positions, where there are not enough GPS satellites, other methods for the ship's position determination are used ? one of those is the relative position determination with taut wire method. The wire is stretched from fixed weight on the seabed to the device on the ship. The angle between the wire and the ship is changed by the ship movement so the relative ship position can be determined by measuring the mentioned angle and the length of the wire. The wire must be taut due to minimization of the influence of sea currents and the tension should be constant. Maintaining constant tension of the wire on the ship in heavy seas is an engineering challenge, which limits the application of this system to relatively shallow and calm sea. The paper describes the development of a modern and reliable electromechanical device that gives the ship’s position in heavy sea conditions. The first step in the development of the electromechanical system for the ship’s dynamic positioning was to analyse the behaviour of the ship on the seas, where this system would be applied. The amplitude and period of the ship’s oscillation depends on the type of the ship, sea conditions, size of the waves, wind and the ship’s position toward them. The influence of sea currents on the angle of the wire is adjusted during the angle measurement. A dynamic positioning device could not be developed without a computer simulation of the dynamic behaviour of the system. The results of simulation provided the basis for the selection and sizing of system elements that can respond to the demands of the required system dynamics. Tension of the wire is held constant by combining the pneumatic system with regulated pressure and electric servo drive. To increase the market acceptability of such device, the manufacturer's intention is to offer it in three variants, each of which is adapted to certain types of ships.