With some useful feedback I updated the TidalCurrents plugin.
The dialog screen
is less obtrusive.
The kmz file on the screen
disappears when the plugin is deactivated, provided you scroll the chart a little.
The plugin will display a kmz area outside the area of the chart in use without crashing OpenCPN
You do need 13 kmz files in the folder you select. HW-6 to HW to HW+6 etc.
No HW or time calculations yet.
HW for some UKHO chartlets people may be using might not be Dover HW.
The updated plugin, libexpat.dll and sample kmz files are here:
Sample is for SW England
I will put the source code on GitHub when it has been tidied up a bit.