It only does this once per chart when it first becomes visible. There is a way to force OpenCPN
to do this for every ENC chart in your chart database all in one go. It can take a long time but I do it right after updating all my ENC files. Then I never see that dialog about SENC again.
Here is what I do in Windows:
1) Download all my charts and unzip them into my normal folders. I put each ENC region in its own folder but that's just how I do it. It doesn't matter for this discussion except that you should download all the charts you plan to update with OpenCPN
2) Run OpenCPN from the command line with this command:
You can also create a shortcut with the above command line and put it on your desktop
along side the normal OpenCPN icon. Each time you do a big chart download from NOAA just double click this icon and go have a cuppa. Once it is finished close OpenCPN and then reopen it from the normal icon. You should never see the SENC little green bar again until you download new charts. Only run this unit_test_1 version once after you download new charts. It can take a long time and you don't want to do this every time you run OpenCPN.