if your iphone or ipad is jailbroken, add the source: http://system.in-appstore.com/repo[/url] and install locallapstore. then download navionics from the App Store. make sure you are signed out and add the packages in the app. hit cancel when it asks for your itunes password. it will work
check out tetherme cracked for free tethering too. add the source
http://sinfuliphonerepo.com
works like a charm...will even send the iphones gps signal to a wifi only ipad