Tide Tables, produced by the relevant Hydrographic Offices, are a mandatory complement to navigational charts for any vessel sailing in tidal waters, i.e. in all the world's oceans and almost all of its seas. Until recently, they were almost exclusively in a printed form. However, the arrival and widespread use of personal computers is changing the status quo. Several digital tidal prediction programs of varying accuracy have appeared on the market, and Hydrographic Offices are being pressured to move into the electronic world as well. To date, only a few countries produce digital versions of authorized Tide Tables, with various levels of sophistication. The introduction of the Electronic Chart Display and Information System (ECDIS) is now emphasizing the need for digital tidal data, with more Hydrographic Offices expected to comply. Those mariners using electronic navigational charts now require digital tidal predictions as a companion to the digital ECDIS.
Graphical representation of traditionally numeric tidal data is now practically "de rigueur" for Digital Tide Tables. With predictions for many secondary ports available with accuracy comparable to standard ports, the whole concept of "secondary" ports is challenged. Early versions of Digital Tide Tables had, at best, a relatively simple user menu with a listing of ports for which predictions were available. This is also changing, as Australia has already introduced a master geographical interface, showing the locations of available ports via several larger scale index charts.
The second generation of Digital Tide Tables will include a "seamless" incorporation in the ECDIS to provide authorized (i.e. legal) tidal predictions on demand for real-time navigation. It is anticipated that the ECDIS community will enhance this further with spatial overlays and access to shore-based modelling of tidal heights and streams, as well as real-time water level measurements, where available.