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                                      NAUTICAL SHAREWARE
(8U (s 0p 10h 12v 0s 0b 3T
                         
     32 Barney Hill Road                     Phone: (508) 358-7938
     Wayland, MA 01778-3602                  email: epwallnr@world.std.com

                               1995 JAN 01

     
     SOURCES FOR TIDE DATA                   
     
     There are several sources of harmonic constants for tide predictions.
     
     The best is the Hydrographic Office of the country where the station 
     is located. The problem here is that some countries charge a large fee 
     for data or are generally unresponsive. (The U.S., Canada, New Zealand 
     and Australia are cooperative and I have most of the data for these 
     areas.) The addresses of the chief hydrographers for member countries 
     of the International Hydrographics Organization (IHO), and for many 
     non-member countries, are given in the IHO yearbook and I can provide 
     this information from the 1992 issue. If anyone gets data from 
     countries not given in the list above I would appreciate receiving 
     copies if that is allowed.  

     The next best source is the International Hydrographic Organization 
     itself as mentioned in TIDES.DOC. Their data sets include up to 62 
     constituents. The IHO's response has been spotty and if the country 
     involved restricts distribution you must still get approval from them. 
     Further a lot of the data is rather old and some has significant 
     errors. Much of the data I have from foreign countries not listed 
     above is from the IHO, either directly of from another sailor and 
     programmer who got the data before all the restrictions were put on. 
     The data is still restricted to non-commercial use, that is you can't 
     sell tide tables or data made using it. 
     
     Another source is the French Service Hydrographique et Oc‚anographique 
     de la Marine (SHOM). They publish the "Table des Mar‚es des Grands 
     Ports du Monde" (TMGPM) which gives ten constituents for 901 ports 
     around the world. This costs 164 francs or about $30 U.S. When using 
     these constants with option H of TIDES the option to include inferred 
     constituents should generally be taken.This will add estimated values 
     of several other constituents. However if the station is near an 
     amphidromic point, as New Zealand is, inferred constituents should not 
     be used. Some stations are marked with one to three asterisks (* - 
     ***) and have sixth diurnal constituents of 10-20, 20-30 or > 30 cm. 
     so that they may have appreciable errors from using just the 
     constituents given or inferred. Except for French ports this data 
     appears to be taken from IHO sources and the comments below apply.

     SHOMAR also puts out the software "Table Universelle des Mar‚es - 
     SHOMAR" for PC compatible computers. This uses the full International 
     Hydrographic Organization (IHO) list of 62 constituents. The program 
     plus constants for 127 stations on the French coasts and Channel 
     Islands costs 1126 francs ($207 U.S.)

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     The tide tables published by the British Admiralty contain the four 
     principal harmonic constants (M2, S2, O1 and K1) for about 4040 tide 
     and 148 current stations world-wide. (For some stations other data is 
     also given from which a few additional constants can be estimated.) 
     Using these constants plus inferred constants a fair approximation to 
     the constituents can be made in most cases, though the comment above 
     on amphidromic points applies. (See ATTDATA.DOC) 

     There are a few things to watch out for with non-U.S. data generally. 
     The datum level to which the tides are referred may not be the same on 
     the charts of different countries and there may also be some other 
     small differences in definitions of constants. Also some data is given 
     in metric and some in English units. (The fellow from whom I got much 
     of the IHO data converted it all to English units. There is a switch 
     in TIDES to change units.) 

     Schureman's "Manual of Harmonic Analysis and Prediction of Tides" 
     (Special Publication No. 98) and the supplement "Conmputer 
     Applications to Tides in the NOS" are available from:
        NOAA/National Ocean Service
        1305 East/West Highway
        Silver Springs, MD 20910-3233
     The price is $5.00 each postpaid in the U.S. I have a few copies which 
     I can send at my cost plus $3.00 postage for one or both. Foreign 
     postage should be based on 19 oz. (540 g.) for SP98, 8 oz. (230 g.) 
     for the supplement and 3 oz. (85 g.) packaging.

     Ed Wallner