In 1998 the IMO recognised that it would take some years to complete the world’s coverage of ENCs. As a consequence IMO ECDIS Performance Standards were amended adding a new optional mode of operation of ECDIS, the Raster Chart Display System (RCDS) mode4. In this mode RNCs can be used in ECDIS to meet SOLAS carriage requirements for nautical charts. However, this is only allowed if approved by the Flag State. The intention of those changes was to allow the ECDIS to operate as far as possible on official chart data; official ENCs where they were available and official RNCs to fill in the gaps.
IMO took note of the limitations of RNCs as compared to ENCs5, and the revised ECDIS Performance Standards require that the ECDIS must be used together with “an appropriate folio of up-to-date paper charts” for the areas where RCDS mode is employed. The intention was to allow the number of paper charts carried by a vessel to be reduced where RCDS mode was employed, but only to a level compatible with safe navigation. No definition of an “appropriate folio” was provided by IMO and consequently different Flag States developed individual interpretations.
As there is no common interpretation of the term “appropriate” ship owners should consult their flag state as to whether RCDS mode is allowed and under what conditions.
In areas where ENCs or RNCs are not available vessels must carry all paper charts necessary for the intended voyage.