TIDE98   (tide level calculator with link to GPS)
Version 2.3  (TIDE983.ZIP - November 1999)
Jean-Yves  Pontailler

                   DISCLAIMER

This program has been tested and should run
successfully on your Series 3a/c/mx. 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
The .ZIP archive contains the English version
together with the French version. To install the
English version, copy the file TIDE983G.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 year 2000 but the
program is able to run without it. If you are
interested in an on-line help, copy 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.

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, 20 or 15 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
supply 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 the tide, try Ocean by
Pierre Pellot, it works extremely well !

If the Series 3a/c/mx 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, course 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.

For more details on tides, see appendix 1. The
calculation mode used by TIDE98 is evoked in appendix
2. If you are already using a former version of
TIDE97 or TIDE98, have a look at appendix 3.

MAIN PARAMETERS (initial dialog)
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 program will be more accurate if it refers
to the nearest high tide.
- The maximal tidal range in the concerned zone. This
parameter is constant for a given site. Some tidal
ranges are given below for about 60 harbours in
western Europe (appendix 4). For other locations,
you can contact me or have a look at this site :
        http://www.shom.fr/

The tide coefficient for the current day is supplied
(for 2000) 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. Type in a
coefficient within the valid range (20-120).

The initial dialog may also display some warnings on
the top left if the program has to use an estimated
tide time or if it is unable to perform such an
estimation. Another warning appears if no TIDE.DAT
file is present for the current year.

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, 20 or 15 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 program 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.

DISSYMMETRICAL TIDE WAVE (English Channel)
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 initial 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 min) but increases up to +45
min 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 min). 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 30 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, one must take
into account the magnetic declination (to be set 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 the
course.
*Updating rate : you can update the display every 60,
30, 20 or 15 seconds.
*Geodesic system : coordinates from GPS can be
displayed (and saved) either in EUROPEAN 50 or in WGS
84 system.
*Daylight savings time : TIDE98 activates D.S.T. from
days of year 86 to 302. D.S.T. is not needed for tide
calculation (providing you supply the local tide
time) but for solar azimuth only. You can modify this
setting in "Options". 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 + drying height.
*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
course,
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.

To achieve the connection please refer to appendix 5.

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/mx. 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 course 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 CALCULATIONS
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" requires
coordinates expressed in degrees (ddd.ddddd),
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.

                    ************

Appendix 1 : 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 on
the TV. As it is not the case in other countries, the
program will load it every day of 2000 from the
TIDE.DAT file.

Appendix 2 : 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.

Appendix 3 : upgrading TIDE97 and former versions of
TIDE98
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 1999.
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,
2.1 or 2.2 to v. 2.3) requires the replacement of the
application file (.OPA) and that of the help file if
necessary.

Appendix 4 : 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   Saint-Nazaire : 6.50 m
Ile d'Yeu (Port 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

Appendix 5 :  Connecting to the GPS receiver
- Psion 3a
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).

- Psions 3c and 3mx
The easiest way to achieve the connection is to buy
from Garmin a cable for transferring data to a PC.
Then connect this cable to the cable provided with
psiWin by the means of a null-modem adapter.


                   ************

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/mx
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 his Psion
Nautical Site, you will find there excellent
software.

          http://p.pellot.free.fr/

A French version is also present in the ZIP archive.
Have fun
