do over 850 marine maps for £25 with 5 mobile device licenses or £50 for 5 mobile + laptop/pc.
These are downloadable onto your phone/tablet and together with the built-in gps can track your position etc.
I've bought them recently and find them very good. you do however have to download each chart at multiple resolutions which took me a while to work out how to do. There is no download all unfortunately
But for £25 it's a slight inconvenience.