It is probable that Congress will require oceangoing ships in US ports to use Differential GPS (DGPS) and electronic charts once DGPS is available on all coasts of the US, which is currently scheduled for completion by the end of 1996. The type of electronic chart currently envisaged, the Electronic Chart Display and Information System (ECDIS) under development by the IMO & IHO, is unsuitable for those ports which are entered through long dredged channels – a category that includes Houston, Gramercy and New Orleans, the three ports which handled the most foreign tonnage in 1991. A different type of electronic chart has been in daily use in such channels, with microwave positioning, since 1984; the combination of DGPS with such a software package has been called an Electronic Navigation System (ENS) and differs from ECDIS in that the ENS is designed to supplement the published chart, not replace it. The paper suggests that the utility of ECDIS would be enhanced if its specifications were modified to allow the entry of the data files used by the ENS, thus giving ECDIS a similar capability for blind navigation in confined waters. Standardization of the current data format would also permit alternative versions of ENS to be developed.