No go zones are polygons created by the user that will be avoided by the routing algoritm if selected.
They are frequently used to avoid sailing in Traffic Separation Scheme (TSS), avois shalow or danger areas…
To create the no go zones:
I recommend that you first select the option to enter waypoints and other “points” on the map at the center of the screen as opposed to where you pressed the screen. The input, if less natural, is more precise. To do do go to the General section of the Settings menu and select the Waypoints at screen center option.
center the map where you want to start your no go zone
long press the screen
select the “No go zone” menu
select the “Create a no go zone” menu
enter a name for the no go zone or leave the default one and press Ok . The first point is created
move the map where you want to continue your no go zone
long press the screen and select “Add a point to the no go zone”
repeat the 2 previous action until your no go zone is complete
Then in the routing menu, make sure you have checked the “No go zones” option.