There is a free e-chart of the Wayfarer Worlds and Rally sailing area available here: http://www.vaarkaartfriesemeren.nl/ As far as I know it is only available for Windows and Android and the site is Dutch only. So, charge your phone or tablet and go for it!
Windows users press the “Nu downloaden” button on the web page. (Alternative: Use Google translate on the web page). Android users: Go to Google play store and search for “Vaarkaart Friese Meren” by a company called “Stentec”.