Digital Tide Tables - A necessity for navigation in the electronic age

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 wi despread use of personal computers is changing the status quo. Several digi tal tidal prediction programs of varying accuracy have appeared on the mark et, and Hydrographic Offices are being pressured to move into the electroni c world as well. To date, only a few countries produce digital versions of authorized Tide Tables, with various levels of sophistication. The introduc tion 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 no w require digital tidal predictions as a companion to the digital ECDIS. Graphical representation of traditionally numeric tidal data is now practic ally "de rigueur" for Digital Tide Tables. With predictions for many second ary ports available with accuracy comparable to standard ports, the whole c oncept of "secondary" ports is challenged. Early versions of Digital Tide T ables had, at best, a relatively simple user menu with a listing of ports f or which predictions were available. This is also changing, as Australia ha s 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" inco rporation in the ECDIS to provide authorized (i.e. legal) tidal predictions on demand for real-time navigation. It is anticipated that the ECDIS commu nity will enhance this further with spatial overlays and access to shore-ba sed modelling of tidal heights and streams, as well as real-time water leve l measurements, where available.