Tides and Currents

Notes

Tide and Current predictions are not available for all areas.
OpenCPN comes with a built in tidal data file, but can use any legacy IDX or binary tcd file. Multiple tidal files can be used at the same time. More about this further down this page.
As with all predictions, the displayed values are calculated using mathematical models and actual tides and currents will vary

Click the toolbar button to see tide stations.
Select to see current stations.
Important: tide and currents will not be displayed unless these toolbar buttons are selected.

Available tide stations will show on the chart as green graphs with a "T" logo:
The "T" becomes a yellow and blue vertical bar when the scale is greater than 1:500.000

The vertical bar contains a lot of information at a glance.
The tidal rise is 2.5m above the chart datum. The blue part is "water". The "V" inside he bar indicates that the tide is decreasing towards Low Water.
Here, the tide is rising towards High Water.
Low Water looks like this.
High Water Looks like this.
Right click the middle of either icon to see the tidal graph:

If a waypoint, route or a track is, or passes, on top of a tidal icon, a rightclick will show a context menu for those features. To see the tidal graph, press "Show Tide Information" at the bottom of the menu.

The Tidal Dialog gives the name of the station as well as the the name of the Data Source file. This is important when you have multiple sources covering the same area. Time and height for HW and LW is displayed in the upper right part.

The Yellow box, with the tidal rise and time, follows the cursor when hovering over the dialog. The time axis at the bottom displays the time, in this case he timezone is "Z +01:00", which is the same as one hour ahead (east) of UTC, that used to be called GMT.
In North America it is common to use a three or four letter acronym for timezones.

CODE	UNITED STATES TIME ZONE CODES	UTC OFFSET
AST	ATLANTIC STANDARD TIME	UTC - 4
EST	EASTERN STANDARD TIME	UTC - 5
EDT	EASTERN DAYLIGHT TIME	UTC - 4
CST	CENTRAL STANDARD TIME	UTC - 6
CDT	CENTRAL DAYLIGHT TIME	UTC - 5
MST	MOUNTAIN STANDARD TIME	UTC - 7
MDT	MOUNTAIN DAYLIGHT TIME	UTC - 6
PST	PACIFIC STANDARD TIME	UTC - 8
PDT	PACIFIC DAYLIGHT TIME	UTC - 7
AKST	ALASKA TIME	UTC - 9
AKDT	ALASKA DAYLIGHT TIME	UTC - 8
HAST	HAWAII-ALEUTIAN STANDARD TIME	UTC - 10
HADT	HAWAII-ALEUTIAN DAYLIGHT TIME	UTC - 9
SST	SAMOA STANDARD TIME	UTC - 11
SDT	SAMOA DAYLIGHT TIME	UTC - 10
CHST	CHAMORRO STANDARD TIME	UTC +10

Available current stations will show on the chart as orange diamonds, when zooming in arrows will appear pointing in the direction of the set. Note that "current" here is short for "Tidal Current", and is the same as the UK term "Tidal Stream".
Master current stations are shown like this in all scales. No direction is associated with these stations but they can be queried, trough a right click, for the magnitude of the current.

Arrow indicates current direction and strength - the bigger the arrow, the more current.
The size of the arrows can be customized by users in the opencpn.ini (opencpn.conf) file.
In the [Settings/Others] section you can set the option CurrentArrowScale to a positive number representing a percentage scaling factor of the current arrows. The values bellow 100 mean the arrows will be smaller than now, the values above 100 will cause them to be bigger.
Right click the orange box to see current graph:
If a waypoint, route or a track is, or passes, on top of a current icon, a rightclick will show a context menu for those features. To see the current graph, press "Show Current Information" at the bottom of the menu.
The Yelow box, with time,speed and direction, follows the cursor when hovering over the dialog.
Note that OpenCPN can only display "Reversing Currents" found in restricted waterways, such as rivers and straits. The general case with "Rotary Tidal Currents", can not be displayed with this interface, but are available for some areas as Grib files. More here Grib Weather Plugin .

OpenCPN supports two tidal file formats. Xtides .tcd file format as well as the default .IDX type. The latter consits of a pair of files called HARMONIC and HARMONIC.IDX, in a directory.
The default, IDX dataset for tides and currents is limited, mainly for copyright reasons.
Xtide, a well known free software tidal aplication (GPL license), maintains regularly updated .tcd files for US, UK and the Netherlands. These are presently the only areas with, up to date freely available, tidal data. The latest updates are available from the Xtide site, http://www.flaterco.com.
A number of different datasets are available on the Internet, with vastly greater coverage. Some of these datasets are quite old, and they also contains glitches and errors, many of which have been corrected in the OpenCPN default dataset.
In many areas there are no free alternatives, and OpenCPN makes it possible to switch between data sets and even using them at the same time. If two stations are located on exactly the same position, only one will be visible......
Go to Options->Charts->Tides & Currents. Press "Add Dataset.." to add another dataset.
Tidal files can be located anywhere on your file system, but it will pay off to be organized. The first entry above shows the default location for the built in datafile on Linux. On windows a typical location is "C:\Program Files\OpenCPN\tcdata".
The last two entries above are the latest available Xtide tcd files.