## 3 Research Methodology  
The research methodology has used two interrelated, separated parts: (i) the segment of _ECDIS_ Experience, Handling, and Opinion (_EHO_) research and the (ii) Human Machine Interface (_HMI_) survey.  
The _ECDIS__EHO_ research has started in the first years of the implementation period to improve educational processes and to develop an appropriate curriculum to increase the level of knowledge of the Officers of the Watch (OOW), being the true system end-users. One of the research tools has been an international questionnaire consisting of introductory and topic-related questions, providing feedback received from navigational ranks and, to a lesser extent, from apprentice officers and other system stakeholders.  
The previous research results and findings have yielded several scientific, educational and practical contributions, reflecting, among other things, in educational process improvements [13; 16; 18; 19; 20; 22; 23; 24]. Recognized key observations have served as an additional factor for the proposed study. While the distribution and analysis of the questionnaire ended on 1 st of July 2018, the research continued further in different segments. On November 2018, the _HMI survey_ was distributed to the international maritime professionals, containing 19 introductory and topic-related questions. Representing a continuation of the research, a dedicated online survey was distributed to the navigational ranks who have obtained the _Generic ECDIS certificate_ at least. The concept of the ECDIS__EHO_ survey methodology has been presented in Figure 3, with the HMI segment added as well as incorporated after the implementation period.  
Figure 2: Counts (x-axis) of feature comments (y-axis) on advantages (lower image: system supporters) and drawbacks (upper image: traditional supporters) of ECDIS navigation compared with traditional means adopted and modified from [20].  
The subject of this research has been the opinion and the mindset of current navigational ranks, which have had the opportunity to work with both types of the navigational means. The research has focused on eligible navigational ranks: masters, staff captains, chief officers, safety officers, 1 st officers navigation, second officers, and the third officers. The following introductory questions have been used in both the surveys to categorise the respondents' profiles:  
* rank,
* working experience,
* holding the ECDIS Generic Training Certificate, and
* holding the type specific/ECDIS manufacturer-approved equipment-specific training.  
The following topic-related questions from _EHO_ and _HMI_ segments/questionnaires have been analysed, with the _EHO_ part providing a possibility of accompanying comments to possible _YES/NO_ answers:  
* _Do you agree with the withdrawal of paper charts from service if certain conditions are met regarding the ECDIS system, i.e., there is no further obligation to possess the same? You can explain the YES/NO answer if you want to._ (abbreviated further as _Q1__EHO_),
* _Do you think that it is still necessary to keep navigational paper charts after implementation of the mandatory ECDIS system?_ (abbreviated further as _Q2__HMI_).  
At this point, the collected answers have been regrouped in the main research categories', containing introductory and topic-related questions, i.e., their responses.  
Respondents have been categorized according to navigational ranks, years of sea experience, and ECDIS-related certificates' holders. Summarized results have been given for the _Q1__EHO_ and _Q2__HMI_ questions. The EHO segment comments have been categorised and discussed in the respective section. The obtained results, analysis, and discussion have been presented as follows.  
Figure 3: The concept of the ECDIS Experience, Handling, and Opinion (EHO) methodology with the Human Machine Interface (HMI) segment adapted, modified, and complemented on the basis of [5].