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A short selection of some tide prediction software and application useful in the Mediterranean Sea

Article by
Paolo Ciraci

Published by nautica
434-June 1998

Translated from italian version: Amare la marea

LOVING TIDES

Since I was a child, the natural phenomenon of the tide greatly fascinated me. The page of the "Children Encyclopedia" with two black and white photographs of Mont Saint Michel, "island" and "peninsula", will always be in my childhood memory. My interest is widely shared by other Italian yachtsmen who repeatedly request information on tide forecast programs via E-mail even if this phenomenon is not particularly relevant for navigation and safety at sea in the seas surrounding Italy. As a matter of fact, the range of the tide in this area is of 1'8" from the mean level; in Genoa, the high tide is of approximately 1'4" in the spring tide and of 8" in the neap tide. In the upper Adriatic Sea the situation is slightly different. Here, the tide may exceed 2'11"; in Venice, particular meteorological conditions (southeasterly wind and low pressure) and oscillations of the Adriatic Sea (the so-called "sesse") determine the phenomenon of the "high waters".

Even if the tide levels in the Italian seas cannot be compared with the levels existing in Normandy or in Cornwall - in Mont Saint Michel the tide may reach a maximum of 52'6" - some tide forecast programs include data regarding several Italian locations.

Tide & Currents for Windows

The latest version (2.5) of Tide & Currents for Windows (T&C) produced by the Nautical Software of Portland (USA) was recently published. Official data of thousands of sites all over the world obtained as a result of an agreement with the British Admiralty may be used with this new version of the program. There are 13 "Tidal Disks" of 13 corresponding regions: Italy is included in the disk n. 2 with 34 locations. T&C is probably the most sophisticated tide forecast software on the market today, covering the time span 1901-2100. As opposed to the vast majority of programs of this type that use little initialization constants, all 223 harmonic components that make up the forecasting model of the UKHO (United Kingdom Hydrographic Office) are supported for maximum processing precision. In addition, Chart View, a powerful electronic chart software produced by the same Oregon-based company perfectly integrates T&C. The T&C program costs USD 129, including the NOAA database of either the U.S. East or West Coast (USD 179 for both databases). The "Tidal Disks" with the Admiralty data cost USD 75 each. Even if it seems a bit too expensive, one should keep in mind that the price includes the royalties to be paid to the British governing department. It is strange that no offer includes T&C with a Tidal Disk instead of the two American databases. Whoever is interested in the tides of the Mediterranean Sea alone, must pay at least USD 204 (USD 129 for the program with a NOAA database and USD 75 for Tidal Disk n. 2). Another flaw is the absence of a demo version of the program, that could eventually be limited in time or to certain locations and that is generally offered by most software companies. The web page of Nautical Software includes extended information on the program and a detailed description of how it works. The reliability of the forecast, limited to the NOAA database and to the present day or to the following day, may be tested in a web page available to all Internet users.

Wxtide for Windows

Wxtide 2.2 is the Windows 95 version of the famous Xtide for Unix, used by some web pages such as Excite Weather or WWW Tide/Current Predictor. The shareware produced by Mike Hopper includes a database of over 7,000 locations all over the world - 34 of these are in Italy and were taken from Tide 2.4, the old MS-DOS program by Hans Pieper. I contributed to a very small extent to the most recent version of Wxtide, published at the end of March, by showing the author some of the main defects we found whenever we tried to obtain the forecast of several sites in the Med Sea. Even though the program is extremely easy to use, it may be customized and configured, both using a menu as well as directly from the toolbar - the latter is almost always absent in Windows programs. In addition, it is possible to choose a location by clicking on a digital map of the world: it is a pity that regional maps are not available at the moment. The user may choose measuring unit (feet or meters), time format (12 or 24), time (local or UTC), date of reference, number of desired days and many other options. The aspect of the generated graph may be selected by setting colors and trend (full or empty) and visualization of the lunar phases and of average level of the tide is possible. One of the most interesting characteristics of Wxtide is the possibility of creating, in addition to the wave graph, useful diagrams with week, month or annual data not only with the timing and the level of the high and low tides but also with sunrise and sunset time and moon rise and moon set time. This program is excellent, above all if one considers that it is completely free of charge.

Swtides 2.26 is an MS-DOS tide forecast program produced by the Canadian-company Stormy Weather Software. The world database includes 951 locations, 16 of them are Italian. The demo version may be unloaded from the Internet and it works very well but for only 10 times: too little for the expensive registration cost of USD 95. If compared with other programs, Swtide is less precise as far as Italian data are concerned. My suggestion is to test and compare the data processed by the different software programs, including old programs of official tide tables, in order to choose the program that gives less average errors for the requested localities.

Paolo Ciraci Il Cybernauta
Salone Nautico Internazionale di Genova
K16PC71-articoli