Getting the tide function to work OpenCPN - OpenPlotter

The Tides feature of OpenCPN does not include world-wide tidal stations.  So this means depending on where you are in the world the tide function for the area you are displaying on OpenCPN will either work or it won't. If you have found you cannot see tide information when you turn on the tide function in OpenCPN here is how we did it. I will do a PC installation first then move on to our OpenPlotter.

After replacing the supplied tide and current data with new files we have tide data at our finger tips.

On a fresh install of OpenCPN you will need to replace the files in the tcdata folder.

Firstly make sure OpenCPN is not running.

PC 
For OpenCPN installed on a PC go to the folder C:\Program Files (x86)\OpenCPN\tcdata to replace the existing files. The files are names HARMONIC.IDX and HARMONIC.

I downloaded the replacement harmonic files here tcdata-2023.zip 

If you would like a link to Terry's topics with up to date waypoints and mbtiles or KAP  and general info great for any cruisers in the east click here. On the page is a handy reference to set up OpenCPN for new users

I created a new folder in the tcdata folder called old harmonic and copied the old files into it. I then copied the tcdata.zip file into the tcdata folder and extracted the contents.

tcdata.zip extracted into C:\Program Files (x86)\OpenCPN\tcdata

Now launch the OpenCPN program and go to Options/Chart Files and click on the ‘Tides & Currents’ tab, then ‘Add Dataset..’, and navigate to where you have saved the ‘tcdata’ folder, open it and select the ‘HARMONIC.IDX’ file, click on ‘Open’, then click on ‘Apply’ and ‘OK’.

Now launch the OpenCPN program and go to Options/Chart Files and click on the ‘Tides & Currents’ tab, then ‘Add Dataset..’, and navigate to where you have saved the ‘tcdata’ folder, open it and select the ‘HARMONIC.IDX’ file, click on ‘Open’, then click on ‘Apply’ and ‘OK’.

Open the chart panel options and select show tide stations. 

What to look for tide station local to your location.

Tide station are easier to see at lower zoom levels.

In the above screen capture when at this zoom level, at a glance  you can see the state of the tide e.g flowing or ebbing. Above we see the arrows denote the tide direction and it is just about full tide as can be seen from the next screen capture below.

Right click on the tide symbol you require information of and this window will pop up.

OpenPlotter
For OpenCPN as part of the OpenPlotter package the install is similar but will require you to type in some commands in a terminal window. more on this later.

I start by downloading the zip file from the web straight into the Downloads folder of OpenPlotter. The file tcdata.zip.

The file is down loaded to the Downloads folder as seen here.

The file is extracted into the Downloads folder.

Right click on the tcdata.zip file and extract here. 

tcdata.zip file has been extracted to the Downloads folder

The files inside the extracted zip file need to be moved to the folder  /usr/share/opencpn/tcdata/ however there is a complication and you will not be able to copy the files directly to the folder using File Manager. This is so the files can be protected and to move the files into this folder requires the use of the sudo command in a terminal window. This allows the operator to assume the identity of the administrator (root) to move files around the system.

First up you need to open a terminal window.

Click on the raspberry symbol on the top left of the screen and select Terminal from the Accessories menu

A terminal window will open up. .

After the tcdata has been extracted to the folder in Downloads I  use the following commands, for more information look at the screen capture of the terminal window to see all the commands necessary to do the job.

The Commands and session used in the terminal window are listed below. 

The commands used to move over the newly downloaded files.

cd /usr/share/opencpn/tcdata will move you to the folder where the tcdata files are stored 

ls command lists the contents of a folder, in this example of the  /usr/share/opencpn/tcdata and as can be seen the answer is the two files HARMONIC and HARMONIC.IDX

sudo mkdir oldtcdata this command makes a folder called oldtcdata

sudo mv HARMONIC HARMONIC.IDX oldtcdata will move the two files HARMONIC HARMONIC.IDX to the folder called oldtcdata.

cd command changes directory (folder) in this instance cd /home/pi/Downloads/tcdata moves to the /home/pi/Downloads/tcdata folder.

ls command lists the contents of the folder in this example the reply is the two files HARMONIC and HARMONIC.IDX

sudo mv HARMONIC HARMONIC.IDX  /usr/share/opencpn/tcdata moves the two new files to the folder /usr/share/opencpn/tcdata  to be used by OpenCPN.

ls  /usr/share/opencpn/tcdata command lists the contents of the folder  /usr/share/opencpn/tcdata  and as can be seen the two files HARMONIC, HARMONIC.IDX and the folder oldtcdata.

So if these files are there then you should be ready to go, start up OpenCPN and see if you can see an tidal stations in your area.

Now launch the OpenCPN program and go to Options/Chart Files and click on the ‘Tides & Currents’ tab, then ‘Add Dataset..’, and navigate to where you have saved the ‘tcdata’ folder, open it and select the ‘HARMONIC.IDX’ file, click on ‘Open’, then click on ‘Apply’ and ‘OK’.

Open the chart panel options and select show tide stations. 

Tide & Current Infomation

Websites we use for tide information:

Tides and currents:
Web sites we find very helpful.
Tide forecast, a world wide tide forecasting site. We have found them to be fairly accurate in Asia.

Department of Survey and Mapping Malaysia, reports the major Malaysian ports tide times and heights. This link takes you to the main page. Scroll to the bottom of the page where you will find the Tide Forecast Table. Just select the closest port to your location. 

Tidetech is a very informative web site detailing ocean and tidal currents world wide. If you have ever tried to get your head around the currents in the Singapore and Malacca Strait this will shed light on this and many more, this did have a great free trial that has since been removed which was great for those one off's when you transit Singapore Strait or the Malacca Strait. However if you have the money they do have subscriptions and at the time of writing this it was 9 euro you get an month of information. For 9 euro you could almost save that in one transit and still arrive quicker.   

Tide Programs for your PC when off line:

OpenCPN: We use the tide and current information in OpenCPN now that we have worked out how to get it working. If you run OpenCPN and find its not working where your sailing you could try and change the tcdata file used to predict the tides.  There is how we did it on our PC and Raspberry Pi running OpenPlotter here and here is a setup guide for OpenCPN down load the latest  PDF or DOCX file open it and scroll down looking for   "Terry's tips rev ?" and there is also a guide to get the tide function working in other places in the world besides the US and Australia.  

For worldwide there is also a free download shareware from the UK Hydrographic Office, TotalTide 1.0.11.0 software gives users access to detailed tidal information for over 7,000 ports and 500 tidal streams worldwide. We have used it and found it to work well. 

WXTide32 we use this and while its not always exact, however it is in the ball park as far as time and heights are concerned.

XTide was designed for Unix and X11, not Microsoft Windows, so if your savy with Unix, here is the original version.

For Australia, PNG, Solomons, Timor there is a free download from the Australian Hydrographic Office for a install program for the coming years tides. 

Tide Predictions for Australia, South Pacific and Antarctica: Online

Tide Predictions for Australia, South Pacific and Antarctica < internet required

http://www.bom.gov.au/australia/tides/

Willy Weather can drill down tide time for different locations in the same bay (e.g Peel Island in Moreton Bay)< internet required

https://tides.willyweather.com.au/

Tide tables for Australia and a tide prediction program < Stand alone once installed

https://hydro.gov.au/webapps/jsp/downloads/products.jsp

Currents 

Forecast and past tidal currents for the Au east coast 

https://oceancurrent.aodn.org.au/tides/index.htm

DownLoad the KML file for Google Earth overlay tidal currents for the Au coast 

https://oceancurrent.aodn.org.au/GE.php

East Coast Current

Queensland section

http://www.bom.gov.au/oceanography/forecasts/idyoc300.shtml?region=SEQLD&forecast=SSTCur

NSW section

http://www.bom.gov.au/oceanography/forecasts/idyoc300.shtml?region=NSW&forecast=SSTCur

IMOS Ocean Current home page

https://oceancurrent.aodn.org.au

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Tidal Stream – Computation of rate

Range of tide for day
_________________         x Spring tide rate of tidal stream
Spring tide range

Why do we need to know this? It’s for working out tidal drift.  If the chart has a tidal arrow its value should have been referenced to the spring tide rate. So if you are there in a neap tide and require the tidal rate this is the formula to use for the job.

Or the easy way, if you have integrated instruments connected to the chart plotter, in most cases the drift/tidal rate can be displayed, the chart plotter uses data from several inputs to calculate tidal drift when on passage.  However this doesn’t work when passage planning. If the chart has tidal diamonds then you will have a good source of rate and direction. Not all charts have these tidal diamonds but have tidal arrows so if you can remember the formula for the computation of tidal rate it may help get you out of a slow trip. 


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Assuming that the tide in your area has a normal semi-diurnal cycle, The rules of 12ths can be used to provide a quick estimate of the height and flow of the tide for times in between high and low water.

For the first hour of tide one 12th of the tide will move
For the second hour of tide two 12th of the tide will move
For the third hour of tide three 12th of the tide will move
For the forth hour of tide three 12th of the tide will move
For the fifth hour of tide two 12th of the tide will move
For the sixth hour of tide one 12th of the tide will move

1+2+3+3+2+1=12