TIDE98 (tide level calculator with link to GPS) Version 2.2 (September 1998) Jean-Yves Pontailler DISCLAIMER This program has been tested and should run successfully on your Series 3a/c. You can copy and distribute it in its zipped form as long as you don't modify it. TIDE98 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 TIDE982.OPA to an \APP\ directory on any drive. Copy the file TIDE.DAT on an \OPD\ directory on any drive. This file contains the tide coefficients for 1998 but the program is able to run without it. If you are interested in an on-line help, install the TIDE.RSC file in an \OPD\ directory on any drive. The use of Flash disks causes no problem. Then install the OPA file using Psion-I or the "Application" menu. UPGRADING TIDE97 If you are using TIDE97 and if you wish to carry on with it, simply rename TIDE.DAT as COEF97.DAT and install it instead of the previous COEF97.DAT file. This new file contains coefficients applicable to the year 1998. TIDE98 has several improvements compared with TIDE97 (see below). To install it if you have been using TIDE97 previously, you can delete all ancient files : TIDE97.OPO in \OPO\ directory, COEF97.DAT, MARGB.RSC and MARS.INI in \OPD\ directory (the latter file is in the internal disk). The MARK.ODP file, which contains your own GPS data, is unchanged but has to be renamed as TIDE.GPS. Then install the new files as exposed above. Upgrading TIDE98 (from version 2.0 to v. 2.2) requires the replacement of the application file (.OPA) and that of the help file if necessary. BRIEF DESCRIPTION TIDE98 calculates the tide height (above zero on charts) for any coast in western Europe and displays it continuously, the screen being updated every 60, 30 or 20 seconds. For that, the time for the nearest high tide is required, as well as the maximum tidal range in the considered zone (constant). TIDE98 does not predict the time of the tide : you have to enter it (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. If you are interested in a reliable prediction of the time of tides, try Ocean by Pierre Pellot, it works extremely well ! If the Series 3a/c is connected to a Garmin GPS receiver, TIDE98 displays coordinates from GPS. The user can save these coordinates and other data in a database file compatible with the "DATA" application. Distance, bearing and speed are now displayed in this new version. When familiar with the programme, the user has the possibility to adjust other parameters in order to obtain a better fit. 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 TIDE98 I thought it was 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 Oceanographique 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). 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 1998 from the TIDE.DAT 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. This period is about 12 hours and 25 minutes, but is lightly 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. TIDE98 has kept a reasonable size (16k and 21k 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 spot, you will only have to enter the time of the nearest high tide to run it. The following comments also appear in the on-line help in an abridged form. MAIN PARAMETERS When you launch TIDE98, 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 programme will be more accurate if you always enter the nearest high tide. - 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 or have a look at this site : www.shom.fr. The tide coefficient of the current day is supplied (for 1998) if you have loaded the file TIDE.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. You can shift time forwards or backwards using the right or left arrows (15 min step). After 60, 30 or 20 seconds (depending on the option you have selected, default value is 60), the display indicates a tide status : rising tide, tide on the ebb or slack tide. Then the programme runs continuously (no auto shut-off) but you can check the battery level on the status window. TYPE OF TIDE TIDE98 supports semi-daily tides only : two cycles every 24 H 50 mn, i.e. 6 H 12 mn between a high tide and the following (or previous) low tide. Semi-daily tides are dominant in western Europe. 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 important at 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 immediately before and after the considered 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. TIDE98 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. For that, it computes a 50 minutes lag per day, an average value whereas the real lag fluctuates between 25 and 90 minutes. As a result, the estimation of the time of the tide will oscillate around the correct value with an error reaching 120 minutes in the worst cases. The magnitude of this error is not depending on the number of days passed since the last entry. It is always preferable to enter a new tide time from a local tide table. ZERO LEVEL TIDE98 displays the tide level above a "zero level" that corresponds to the minimum effectively possible (in fact, a few centimeters are often 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. You can adjust this zero offset in "Options" if you wish so. 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. Initially, the programme calculates a geographical bearing. To display a compass bearing, you must enter a magnetic declination in "Options". 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 northern hemisphere). OPTIONS This dialog gives access to several settings : *Magnetic declination : if documented, a magnetic bearing is displayed for solar azimuth and for bearing. *Updating rate : you can update the display every 60, 30 or 20 seconds. *Geodesic system : coordinates from GPS can be displayed (and saved) either in EUROPEAN 50 or in WGS 84 system. *Daylight savings time: the estimation of the height 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. Thus, select "Yes" during summer. This won't affect your settings in the "TIME" application. *Reference mark : you can enter a threshold level (rock, anchorage) to be displayed in the tide bar diagram. Enter the sum draught + level above zero. *Zero offset : to adjust the gap between zero level on charts and lowest water level at exceptional spring tides (default value : 0.20 m). DELAYED ESTIMATION You can also calculate the tide level at a time which 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 II, 38, 40, 45, 65 and 75 and enables : 1- to display continuously on the 3a/c the coordinates from the GPS unit (using either WGS 84 or EURO 50 grid), the distance covered, speed and bearing, 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 programme 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/c. In TIDE98 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. Beware, when connected, your Psion draws twice as much power as usual (about 65 mA). In this version, distance, speed and bearing are calculated (using coordinates from GPS) and displayed. The distance is that covered between the connection of the GPS unit and the present location. If you go back to your starting point, zero should be displayed. Use key R to reset. A magnetic bearing is displayed if you enter a magnetic declination in "Options". 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\TIDE.GPS) 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 CONVERSION AND DISTANCE CALCULATION Several converting utilities are available in the "GPS SECTION" menu. Have regard at the format indicated in the dialogs. These routines are totally independent of the other sections of TIDE98. The option "Distance between two points" requests coordinates expressed in degrees (ddd.dddd), negatives values being used for South and West. EXIT When you exit the program, your own settings are saved in an \OPD\TIDE.INI file in the internal disk. This file is created when you launch the programme for the first time. The high tide time is used during the current day only. Every following day, a time lag is added in order to follow roughly the tide schedule. 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 : 7.30 m Dieppe : 10 m Fecamp : 8.60 m Port-en-Bessin : 7.50 m Cherbourg : 6.70 m Portbail : 12.50 Granville : 14.40 m Saint-Malo : 13.40 m Les Heaux de Brehat : 10.70 m Roscoff : 9.50 m Brest : 7.50 m Audierne : 5.60 m Concarneau : 5.40 m Lorient : 5.50 m Belle-Ile (Le Palais) : 5.60 m Houat : 5.60 m Le Croisic : 6.10 m St-Nazaire : 6.50 m Ile d'Yeu (P Joinville) : 5.50 m Les sables d'Olonne : 5.70 m La Rochelle : 6.50 m Pointe de Grave : 5.40 m Arcachon (Eyrac) : 4.80 m Cote landaise : 4.50 m St Jean de Luz : 4.80 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/c users. You can contact me to obtain precise data concerning your favourite spot (especially if it is in France). I am interested in any feedback on GPS link, especially on the accuracy of coordinates using EURO 50 grid or any report on various models within Garmin's range (only models 38 and II+ were tested). 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... Thanks to Pierre Pellot for hosting me on its Psion Nautical Site, you will find there excellent software. http://www.enfrance.com/p.pellot/ Tide coefficients to run TIDE98 in 1999 will be available on this site by Christmas. A French version is also available (TIDE982f). Have fun