## 2 The Role of Measurement in the Ship's Operation Process  
To achieve complete overview of any condition on board considered sea ship, it is vital to measure not only affecting parameters such as flow, pressure, temperature and level [3; 4; 5], but also the operational parameters of main engine, or more widely--ship propulsion [6; 7]. Special attention should be paid to the measurement systems supporting navigation area [8; 9; 10]. This information allows crew members to take action before changes affect equipment performance and cause downtime or failures. Considering the ship as a measurement and control object, there are different tasks executed in the following areas:  
1. Navigation;
2. Operation of power plant;
3. Operation of cargo system;
4. Ensuring safety of crew, equipment and environment. In the navigation area, these tasks may include:  
* Measurement, filtration and estimation of ship position coordinates (measurement of the position of the ship and foreign ships) for the purpose of controlling its movement along the desired trajectory, position stabilization and use in anti-collision systems;
* Measurement of parameters characterizing movement of the ship (determining the velocity vector, course, draft, trim, side swaying of the ship, wind direction and force). Measurement tasks for safe and economical operation of the ship's power plant, i.e., the main engine and all the mechanisms and auxiliary devices consist of:  
* Measurement of mechanical motion parameters of devices driving the generators and selected characteristic parameters, such as the quality of the fuel fed to them and the composition of exhaust gases;
* Measurement of parameters, in general temperatures, pressures, levels, viscosity and flows at selected points determining operational conditions of the power plant;
* Measurement of torque, power and revolution speed on the shaft of the Main Engine (ME) for the purpose of economical operation of the ship's propulsion;
* Measurement of quantities characterizing the power grid (voltages, currents, powers, frequency, \(\cos\varphi\), insulation resistance, THD--Total Harmonic Distortion);
* Fire protection system. Cargo transportation requires the following measurement tasks:  
* Measurement of cargo parameters that determine its qualitative features;
* Measurement of the amount/weight of the transported cargo;
* Load distribution measurement (loading calculators);
* Measurement of technological media parameters enabling transport of cargo;
* Measurement of water levels inside of ballast tanks. Qualified crew members are required to operate the ships adequately. Ships have to provide proper accommodation and additional systems necessary to support good nutrition and health of the crew while ensuring adequate environmental protection. The following measurement tasks are done in order to fulfil that:  
* Measurement of parameters of potable water system;
* Measurement of parameters of air conditioning system;
* Measurement of parameters of cooling system for food storage;
* Measurement of parameters of sewage system;
* Identification of smoke and temperature of fire alarm system. Safety function of the ship as a whole requires control of limit values and trends in their changes, basic parameters determining safe operation of technical systems and safety of people, cargo and the marine environment. The aforementioned measuring tasks include both operational and diagnostic measurement, but the authors are of the opinion that the latter ones are beyond the main scope of this paper. The purpose of operational measurement is to determine the current value of the parameters of a given system and to check the correctness of its operation and related processes. Operational measurement is used for both manual and automatic remote control, and its main purpose is safe and effective operation of the ship. In case of emergency, vital systems can be controlled locally, where all the system operations are done by the crew directly, sometimes using only human power.