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


Enable Tides and Currents Display

  • 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.

 

Displaying Tides

  • 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


 

Displaying Currents

  • 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 .

 Using an alternative data set

  • The default 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.

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