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6/05/2020 7:02 am  #1


Updating Tidal Currents for Local Area - How to import

I have been using OpenCPN in the past and like the tidal current model used for my local sailing area (Newport, RI and Narragansett Bay) better than the model that Expedition uses.  OpenCPN uses the XTide data in a folder labeled tcdata.  The files in this OpenCPN folder are HARMONIC, HARMONIC.IDX and a README.harmonics file.

The Expedition PDF help file states:
Xtides
Expedition can also use the GNU Xtide software distribution global tidal station database available at http://www.flaterco.com/xtide/index.html.
Download the harmonics.txt file (it may be zipped) and select it using the Xtide button. Be aware that the file contains a large number stations and physically reading it may slow Expedition, so you may
just want to copy the stations you are interested into your own file.
This option is provided merely for user convenience. While Expedition uses a significantly different technique of computing tides to Xtide, the results should be very similar.

I have downloaded harmonics-dwf-20191229-free.tar.xz and extracted the files harmonics-dwf-20191229-free.tcd, ChangeLog and COPYING.

I don't know what folder Expedition keeps the tidal current models and how I access the Xtide button referred to in the help file.

Questions:
1. Can I use the OpenCPN harmonincs files directly in Expedition? If so, how?
2. If not, how do I import and use the downloaded XTide harmonics file?

 

6/05/2020 12:51 pm  #2


Re: Updating Tidal Currents for Local Area - How to import

The Exp format is custom. 

The XTide data should use the same NOAA tides and currents. Have you tried the US East coast currents rather than the model?

The xtide text file is old and the currents don't contain any direction information.

Exp can't read the .tcd file. It has been on the work-list for a long time, so I will have a look at that.

 

6/06/2020 5:04 am  #3


Re: Updating Tidal Currents for Local Area - How to import

Thanks Nick. 

I changed it to the US Model RI & MA and it shows more data points on the chart.  All the labels on the chart are in the format 0.XX.  Is this supposed to represent a factored maximum?  Some current arrows appear over land masses rather than the water bodies.  The screen shots below represent planning I'm doing for a pursuit race in Narragansett Bay on 7 June.  I know that currents may be up ~ 0.7 Kts @ 230 under the Mt. Hope Bridge at 11:06 local and agrees with the local current chart predictions.  My optimal route planning shows set and drift 246/0.0kts as shown in the third screen shot from OpenCPN.  The Mt. Hope Bridge is a mark of the course so a convenient location to look at tidal currents.

How do I clear the XTide file box on the Tides settings screen?  I put an entry in there to try and now I can't clear it.

Links and pictures below:
Optimal Route CSV Output from Exp

Arrows over land Ebb
https://crew-mgr.com/temp/arrows-over-land-ebb.png


Arrows Over Land Flood
https://crew-mgr.com/temp/arrows-over-land-flood.png


Current Mt Hope Bridge - OpenCPN @ 1106 7June2020 
https://crew-mgr.com/temp/opencpn-tide.png

     Thread Starter
 

6/06/2020 12:47 pm  #4


Re: Updating Tidal Currents for Local Area - How to import

The US model data are from a low resolution model. They work better in somewhat more open waters than your a looking at.

The US East Coast Currents option will give you the NOAA tidal currents as you see in OpenCPN.

Just delete the text ...

 

6/08/2020 3:34 am  #5


Re: Updating Tidal Currents for Local Area - How to import

Nick,

The Settings dialog box for XTides is a file chooser. If you delete the text and submit, the only options is "Open" or "Cancel". Neither button saves it with blank text.

     Thread Starter
 

6/08/2020 1:11 pm  #6


Re: Updating Tidal Currents for Local Area - How to import

Deleting the text in the xtide edit window works here. This is v11.

 

6/08/2020 3:18 pm  #7


Re: Updating Tidal Currents for Local Area - How to import

I am running 10.11.1.0 on Win 10 Pro

     Thread Starter
 

6/08/2020 3:52 pm  #8


Re: Updating Tidal Currents for Local Area - How to import

The old v10 framework may be different. You make an empty txt file, point Exp to that and then delete it.

 

6/08/2020 3:57 pm  #9


Re: Updating Tidal Currents for Local Area - How to import

Thanks Nick.  I just did that.  Expedition seems to work fine but the deleted file name remains in the dialog box even after exiting and restarting the program. I don't think it has any adverse impact on the program.

     Thread Starter
 

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