To get any detail on OpenCPN in the UK you will need to buy some charts
, other countries provide them for free, but not the Hydrographic Office.
The Visit My Harbour charts
are £23 for a year and then if used for real navigation
then you should update them. However, if its just route
planning then no need for this.
The alternative is to use the only line Navionics
chart viewer which has a simple route planner:
However, the chart viewer isn't up to date as the Open Seamap for some features, if that is a concern.