TIDE97 (tide level calculator with link to GPS) Version 1.3a (January 1997) Jean-Yves Pontailler DISCLAIMER This program has been tested and should run successfully on your Series 3a. You can copy and distribute it as long as you don't modify it. TIDE97 is used entirely at the user own risk. To reduce this risk, please review carefully this instruction file. When sailing, be sure to check all the local parameters you are using to run it. In all cases, you must absolutely add a large safety margin to the program estimates. Installation Copy the file TIDE97.OPO to an \OPO\ directory on any drive. Copy the file COEF97.DAT on an \OPD\ directory on any drive. This file contains the tide coefficients for 1997 but the program is able to run without it. If you are interested in an on-line help, install the MARGB.RSC file in an \OPD\ directory on any drive. The use of Flash disks causes no problem. Origin and description I have started to write this program last summer for my personal use, to be aware of the tide level when sailing and for mapping purposes. It has grown in an anarchic way since then but it can be of some help as soon as your 3a sees a shore or goes on board. TIDE97 calculates the tide level (above zero on charts) and displays it continuously, the screen being updated every minute. If the Series 3a is connected to a Garmin GPS receiver, TIDE 97 displays coordinates from GPS. The user can save these coordinates and other data in a database file compatible with the "DATA" application. TIDE97 does not predict the time of the tide : you have to key it in (at least once). I have added to this version a very simple follow-up of the tide schedule (day after day), but it has to be handled with caution. From the theory to the application The tide phenomenon appears rather complicated as soon as you try do describe it precisely all over the world. Its cause is astronomical, that is the attraction of the water of the oceans by the moon and, to a lower degree, by the sun. In theory, one must observe two tidal waves in 24 hours and 50 minutes, duration of an apparent rotation of the moon as seen from the earth. **** The time of the tide High tide is supposed to occur twice during this period, once when the moon is above the site and once when it is in the opposite direction, but the presence of continents makes the reality much more complex. As an example, the tide wave should go from east to west through the channel in less than one hour.. but it goes the other way round and takes 8 hours to do so ! **** The amplitude of the tide The intensity of the phenomenon varies according to the respective position of both moon and sun (their effects acting together or opposing themselves), but also depends on the shape of the shore and on the size of the oceans and seas. **** The option chosen in TIDE97 A program could easily take into account the above-mentioned astronomical data but it would be unable to predict the tide time and level without considering the numerous tide-related characteristics of all the sites where predictions are expected. This approach leads to a complex program using a cumbersome database to run successfully on a large scale. I thought that it was more pertinent to make use, in every harbour, of precise local data that are freely and easily available : the time of the high tide, the maximal tidal range (a constant local parameter) and the tide coefficient. The first two of them are easy to find nearly everywhere. By contrast, the tide coefficient exists in France only. **** The tide coefficient It is calculated by the SHOM (Service Hydrographique et Oc‚anographique de la Marine), has no unit and ranges from 20 to 120. The tide coefficient integrates twice a day the astronomical components of the tide. People often suppose that the tide coefficient is valid in France only since it refers to Brest. In fact, it is reliable in a large part of western Europe (showing semi-daily tides). On other continents, a problem may rise, due to the "age of the tide". In western Europe, there is a 36 hours lag between the cause (astral) and the effect (tide). This delay is often shorter in other places (8 hours in New-York), so the tide coefficient applicable will be that of the previous day. In France, the tide coefficient is present everywhere, even at the TV. As it is not the case in other countries, the program will load it every day of 1997 from the COEF97 file. **** Calculation mode The program assumes that the tide wave has a sinusoidal shape and modifies its period and/or amplitude according to the value of several input parameters. In the case of semi-daily tides, the period is about 12 hours and 25 minutes, this duration being weighted as a function of the tide coefficient (the period is longer during neap tides). The program is able to deal with dissymetrical tide waves (ebb taking often longer than flow) if you expect so. TIDE97 has kept a reasonable size (13k and 18k with the two associated files) and usually provides a good fit. When you will be familiar with one or two constant characteristics of your favourite place, you will only need to enter the time of the nearest high tide to run it. I see no reason to make an OPA with such a tiny program, probably because the never-ending row of isolated icons in my system screen makes me feel uncomfortable. The following comments also appear in the help in an abridged form. Main parameters When you launch TIDE97, a dialog appears requiring several parameters. You must at least document two parameters : - The time of the nearest high tide (no matter if it is passed or in the future) in a 24 hour format. If you are sailing in the evening and if the high tide is expected after midnight (so the following day), you can use it but you must type H+24 (i.e. 27 for 3 am). - The maximal tidal range in the concerned zone. This parameter is constant for a given site. Some tidal ranges are mentioned at the end of this file for about 60 harbours in western Europe. For other places, you can contact me. The tide coefficient of the current day is supplied (for 1997) if you have loaded the file COEF97.DAT in any \OPD\ directory. If no coefficient is available, the dialog displays the default value : 20 corresponding to an exceptional neap tide. Enter a coefficient within the valid range (20-120). When you validate the dialog, the main screen appears, showing the tide level on the right. The expected range for the current day is also shown. I have added a tide level expressed in feet. Menu and Help keys are now active. After one minute, the display indicates a tide status : rising tide, tide on the ebb or slack tide. The threshold retained for slack tide is a rise (or a fall) smaller than 0.2 to 1.5 cm per minute (according to the amplitude of the tide). This is not perfect, but it has the merit to indicate weak tidal currents. Type of tide Two types are valid (the most common) : - Semi-daily tides (default) : two cycles every 24 H 50 mn, i.e. 6 H 12 mn between a high tide and the following (or previous) low tide. - Daily tides (not present in western Europe) : one cycle every 24 H 50 mn. The program does not support mixed tides, as observed in west Indies or along the western coast of the United States. Pressure correction An elevated atmospheric pressure lightly decreases the water level. Enter a value for atmospheric pressure (mb), the default value is 1013 mb or hPa. The program applies a correction equal to -1cm per extra millibar. Without correction, an error rises, that can reach 30 cm. This correction is optimized for the channel and may be too high for places experiencing lower tidal ranges. Dissymmetrical tide wave The rise and the fall often differ in duration, the latter being usually longer. If known, this lag can be taken into account. Use the line "ebb-flow differential" in the main dialog. Beware of the sign of "ebb minus flow". The lag is negative in the rare case where flow takes longer than ebb. Default value is 0. Dissymetry is moderate in the western part of the channel (+20 mn) but increases up to +45 mn when approaching the Straits of Dover. This correction is valid only within the two low tides that are on both sides of the selected high tide. If you let the program run further, it will return to a symmetrical mode but you won't notice it since it occurs at low tide during the slack. Accuracy Accuracy is globally satisfying when local parameters are used. Errors are mainly due to the fact that the period fluctuates a little around its average value (that is 12 h 25 mn). This causes discrepancies on the water level that may reach 30 cm. Total error should not go beyond 70 cm in zones experiencing important tidal ranges, when including unfavourable wind and pressure effects. TIDE97 is not a tide time calculator but, if you have used it at least once, it will propose an estimated tide time at every subsequent use (semi-daily tide only). For that, it computes a 50 minutes lag per day, an average value whereas the real lag fluctuates between 30 and 90 minutes. As a result, the estimation of the time of the tide will oscillate around the correct time with an error reaching 120 minutes in the worst cases. It is always preferable to enter a new tide time from a local tide table. TIDE97 displays tide levels above a "zero level" that corresponds to the minimum effectively possible (in fact, a few centimeters are added for security). Lower values (negative) should not be displayed, unless you have applied a large barometric correction. This zero level usually corresponds to the zero level on charts but there are some exceptions in UK (zero level=average low level of spring tides) making a correction necessary. Solar azimuth I thought that it could be of some interest to be aware of the direction of the sun. This function uses data from the "WORLD" option, such as the longitude and the GMT offset of your home city (even if a GPS receiver is connected). So you have to select a home city that is close to the place where you are navigating. You can also create one at your convenience. The program displays a geographical bearing. To estimate a compass bearing, you must take into account the magnetic declination (some values are given in the "EXTRA" option of the main menu). The calculation is rather simple and does not take into account the "equation of time" that quantifies the observed difference between the mean solar time and the true solar time. The error is less than 1.5 degree during summer and less than 4 degrees in winter (in north hemisphere). Daylight savings time The estimation of the level of the tide uses the system time, so DST is taken into account. By contrast, the calculation of the azimuth of the sun uses the GMT offset from "WORLD" that ignores DST. In summer, validate the option "Sun azimuth with DST" in the main menu. This won't affect your settings in the "TIME" application. Delayed estimation You can also calculate the tide level at a time that differs from the system time. For that, select the option "Time different from system" at the bottom right of the main screen. Link to Garmin GPS receivers This function should work with models 38, 40, 45, 65 and 75 and enables : 1- to display continuously on the 3a the coordinates from the GPS unit (using the WGS 84 grid), 2- if you wish so, to save these coordinates in real time, together with other information, for example to mark your route or a remarkable diving or fishing spot. This function is useful but is far from a complete GPS utility program such as PSIGAR by Jonathan Duff. **** Connecting to the GPS receiver For this, you need a Psion serial link and a Garmin lead with bare wires. In my opinion, the best way to achieve the connection is to link the bare wires to the podule on the serial link. You have to find a male 9 pin mini-Din plug and solder the three wires as follows : - pin 2 : brown (GPS to Psion) - pin 3 : white (Psion to GPS) - pin 5 : black (ground) The soldering operation will be easier if you first cut the useless pins. To identify the correct pins, refer to the appendix C of the 3-Link manual or to the end of the PSIWIN manual. If you prefer to connect the bare wires to the Sub-9 female plug of the 3-Link, note that the brown wire has to be soldered on pin 3 and the white one on pin 2 (pin 5 being unchanged). **** Achieving the connection As soon as the cable is in place, setup your Garmin receiver to GRMN/GRMN communication protocole and make sure that the Psion link is turned OFF on the system screen of your 3a. In TIDE97 menu, validate the option "Link to GPS". After a control dialog, the link is established and the coordinates from the GPS are displayed in real time instead of those from "WORLD". If you launch the connection with a faulty cable or a GPS not being set for the correct protocole, the program will hang up and you will have to exit using Psion-ESC. If you select the "Mark" option (key M), you can save your actual position together with time, date and depth, into a data file. You can document two lines in the dialog : the depth from a depth finder (the program will substract the tide level from it) and a comment (36 characters max.). The data file (\OPD\MARK.ODB) is created in the internal drive when you use the "Mark" function for the first time. You can browse and modify it using the DATA application (it does not appear on the system screen, you must select it with the file manager). You can also add pertinent line titles (time, latitude...). Grid conversions Several converting utilities are available in the "GPS SECTION" menu. Have regard for the format indicated in the dialogs. These routines are totally independent of the other sections of TIDE97. Exit When you exit the program, your own settings are saved in an \OPD\MARS.INI file in the internal disk. This file is created when you launch the program for the first time. The high tide time is used during the current day only. Every following day, 50 minutes are added to it in order to follow roughly the tide schedule (semi-daily tide only). The tide coefficient is not saved since it is retrieved from another data file. Some values for the max. tidal range in western Europe : Northern countries and islands : Arendal : 0.50 m Bergen : 1.60 m Bodo : 3.30 m Reykjavik : 4.90 m Rorvik : 2.89 m Shetland I. : 2.40 m Scotland : Aberdeen : 4.90 m Dundee : 5.60 m Greenock : 4.60 m Inverness : 5.30 m Leith (Edinburgh) : 6.40 m Ullapool : 5.60 m Wick : 4 m Ireland : Belfast : 4.10 m Cobh (Cork) : 4.60 m Dublin : 5 m Galway : 5.50 m Londonderry : 3.10 m Shannon river : 5.30 m Denmark and Germany : Borkum : 3.70 m Bremerhaven : 5.10 m Cuxhaven : 4.80 m Esbjerg : 2.50 m Helgoland : 3.90 m Hirtshals : 0.30 m Belgium & Holland : Antwerpen : 6.50 m Oostende : 6.10 m The hague : 3.10 m Terschelling : 2.70 m Great Britain & Channel Islands : Barrow in Furness : 10.90 m Liverpool : 10.90 m Holyhead : 6.20 m Fishguard : 5.60 m Milford Haven : 7.50 m Swansea : 10.30 m Cardiff : 12.60 m Falmouth : 6 m Plymouth : 6.30 m Torquay : 5 m Lyme bay : 4.40 m Portland I. : 2.90 m Portsmouth : 5.50 m Shoreham (Brighton) : 6.90 m Dover : 8.30 m Sheerness : 6.90 m Harwich : 4.80 m Lowesoft : 3 m Hull : 8.30 m Tyne R. (Newcastle) : 5.70 m Jersey : 11.90 m Guernesey : 9.40 m France : Calais : 8.50 m Dieppe : 10.90 m F‚camp : 8.90 m Port-en-Bessin : 7.40 m Cherbourg : 6.80 m Granville : 14.20 m Saint-malo : 13.40 m Les Heaux de Br‚hat : 10.10 m Roscoff : 9.40 m Brest : 7.10 m Lorient : 5.40 m Concarneau : 5.20 m Saint-Nazaire : 6.80 m Les sables d'Olonne : 5.90 m La Rochelle : 6.80 m Pointe de Grave : 5.40 m Cote landaise : 4.70 m Spain, Portugal, Canary, Madeira & Acores : Bilbao : 4.40 m Santander : 4.70 m La Coruna : 4 m Vigo : 3.90 m Lisbon : 4.10 m Cadiz : 3.50 m Acores : 1.80 m Canary : 2.40 m Madeira : 2.50 m ************ Thanks are due to Jonathan Duff, Simon Pooley and Mike Rudin for their efficient help. I am indebted to the SHOM (Service Hydrographique et Oceanographique de la Marine) for allowing me to give out a file containing the tide coefficients among Psion 3a users. Few developments are planned yet but it will largely depend on you. Feel free to mail me, I will be very happy to read your comments : jean-yves.pontailler@eco.u-psud.fr If you are angry with my bad English, please mail me a few amendments.... This version for UK (1.3a), available at steve's well known "3-Lib" site, uses the international WGS84 grid. A continental version (1.3c) uses the Euro 50 grid. A French version (1.3f) is available at : http://alex.union-fin.fr/usr/dcabuzel/psion/ Have fun