Navigational information systems became one of the main devices on ship’s bridge supporting navigators in evaluation of navigational situation and undertaking decisions. For instance ECIDS supports navigation by gathering information and automating some process like plotting of position of own ship and other objects on the scene. Any navigational information system has got advantages and limitations. Their understanding should help navigators to perform watches in a safer way. This article presents a discussion on some deficiencies of navigational information systems. Discussion is underlined by three accidents, which show when misunderstanding or overreliance may lead to catastrophic consequences
 Bak A., Chomski J., Magaj J., Pietrzykowski Z., Uriasz J., Aims and tasks of the navigational support system on a sea going Vessel, Advanced in Transport Systems Telematics, Katowice 2007.
 Banachowicz A., Wolejsza P., The analysis of possibilities how the collision between m/v Gdynia and m/v Fhu Shan Hai could have been avoided, Advances in Marine Navigation and Safety of Sea Transportation, TransNav 2007, Gdynia 2007.
 BSU - Federal Bureau of Maritime Casualty Investigation: Investigation Report 01/08, Grounding of LT Cortesia on 2 January 2008 on the Varne Bank in the English Channel, Hamburg, 1 April 2009.
 IHO Publication S-52 Appendix 2: Addendum to Annex A, Part 1, Edition 3.4, 2008.
 Lloyd’s Register: Sea-web data base, London 2011.
 MAIB - Marine Accident Investigation Branch: Report No 2/2009, Report on the investigation into the grounding of Pride of Canterbury ‘The Downs’ - off Deal Kent 31 January 2008, Southampton, January 2009.
 MSC: Circ.982, Guidelines on ergonomic criteria for bridge equipment and layout, IMO, London 2000.
 MSC: Circ.1061, Guidance for the operational use of integrated bridge system (IBS), IMO, London 2003.
 MSC: Circ.1091, Issues to be considered when introducing new technology on board ship, IMO, London 2003.
 MSC: Research into interaction with automated systems, MSC 82\15\2: IMO, London 2006.
 NAV: Report to the Maritime Safety Committee. NAV/54/2514, August 2008, IMO, London 2008.