The modern simulation software includes an impact of forces acting on the ship hull. One of the mostsignificant forces is sea waves acting. The mathematical model allows simulation of ship motions in irregularsea wave area, both – at deep and shallow waters. The wave surface model enables simulation of the waveelevation in compliance with wave spectrum occurring in various conditions. The paper presents generaldescription of the sea wave model used in maritime simulators. An example of such simulators is used at the laboratory of the Naval University of Gdynia, where it is operated basing on NT-Pro 5000 software by Transas Marine. The latest version of simulation software gives a possibility to select the wave spectrum. Selection of the waving type, depending on sea area location, makes the ship movement more reliable. This is an important element in testing the ships behavior process

The paper describes a mean of using vessel’s manoeuvring parameters recorded in real conditions for the purpose of analysing the environment influence on ship’s behaviour. This information has also been used to conduct a comparative analysis of a real vessel and its simulation model in the data base of a navigationmanoeuvring simulator. The measurements were taken on an unrestricted sea area so as to eliminate the impact of developed sites on wind field. The research was conducted in the region of the North Sea and Baltic Sea.

This paper presents the authors’ reflections on using integral calculus when preparing the process of locating single ground-based chains of positioning systems in marine navigation. These reflections are purely theoretical and presented research results apply to a hypothetical navigation system that operates based on the ratio of distances, which is regarded as a navigation parameter.

The article by Krzysztof Czaplewski, Sławomir Świerczyński and Piotr Zwolan entitled “Using elements of integral calculus in the process of optimizing the configuration of navigation positioning systems”3 published in the previous issue (45/2016) is an English version of the revised article by Krzysztof Czaplewski “Kryterium całkowe jako narzędzie matematyczne wspomagające proces optymalizacji wystawienia stacji systemu nawigacyjnego” 4, published in ZN AMW No. 3/2000. The authors would like to apologize for having forgotten to include this article in the reference section, which mistake was noticed after the article had been published. The authors' intention was not to conceal the previous publication, but to return to the previous studies on navigation processes optimization devised by one of the authors. The authors considered it desirable to get back to the previous results, as the problems of automatization of optimization processes are still valid in navigation and require further work. Furthermore, the subject of the article lies in the area of studies currently performed by the authors. In the context of increasingly frequent information on spoofing and jamming of satellite system signals, ground-based radio navigation systems begin to grow in significance again. For example, the contemporary mutation of the Loran system called eLoran seems to be at the time the best option supporting the operation of GNSS. The erection of new eLoran stations or other systems supporting the operation of GNSS has to be preceded by reliable optimization studies among others, and this is the reason why the authors are interested in this area of studies. We would like to apologize to anyone who felt offended by the situation. The Authors